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TRANSPORTATION
RESEARCH DIGEST
APRIL 2007
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
The contents of the Transportation Research Digest reflect the views of the authors who
are responsible for the facts and the accuracy of the data presented. The contents do not
necessarily reflect the official views or policies of the Institute
.
2
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
TO: TRANSPORTATION PROFESSIONALS, MANAGERS, & POLICY MAKERS
FROM: ARIZONA TRANSPORTATION INSTITUTE
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A ―Topic‖ code in the Table of Contents will help readers more quickly identify items of
interest. The topic codes are explained in the table below.
Code Topic Code Topic
ADM Administration PLAN Planning
AIRP Airports PRIV Privatization
AVIA Aviation RAIL Railroads
BIKE Bicycles RDSD Roadside
CON Construction ROW Right-of-Way
ECON Economics SAFE Safety
ENV Environment STR Structures
FIN Finance TECH Technology
INOV Innovations TOLL Toll Roads
MAIN Maintenance TRAN Transit
MISC Miscellaneous TRF Traffic
MVD Motor Vehicle Dept TRK Trucking
PAVE Pavement VEH Vehicles
Requests or inquiries may be made via e-mail (jsemmens@cox.net).
Thank you.
4
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
TABLE OF CONTENTS
Topic Title Pages
CON/ Performance of a Pile-Supported Embankment by Edward J. Hoppe and 9-10
embank- Stanley L. Hite, Virginia Transportation Research Council, 530 Edgemont
ment Road, Charlottesville, VA 22903 (Virginia Department of Transportation, 1401
E. Broad Street, Richmond, VA 23219) (Jun 2006) Significant savings can be
achieved on pile-supported embankment projects because of the relatively high
material costs involved in this type of construction.
CON/ Stability of Column-Supported Embankments by George M. Filz and Michael 11-12
embank- P. Navin, Virginia Transportation Research Council, 530 Edgemont Road,
ment Charlottesville, VA 22903 (Virginia Department of Transportation, 1401 E.
Broad Street, Richmond, VA 23219) (Jun 2006) Numerical analyses of slope
stability are needed to capture the realistic failure modes that can control
embankment performance.
ENV/ Tires and Passenger Vehicle Fuel Economy by Committee for the National 13-14
fuel Tire Efficiency Study (Transportation Research Board, 500 Fifth Street, NW,
economy Washington, DC 20001; (202) 334-3213; http://gulliver.trb.org/bookstore)
(2006) A 10% reduction in tire rolling resistance promises a 1 to 2% increase in
the fuel economy of these vehicles.
MAIN/ A Synthesis to Improve the Design and Construction of Colorado’s Bridge 15-16
anti-icing Anti-Icing Systems by Gordon T. Bell, Wilfrid A. Nixon, Robert D. Stowe,
Bell Enterprises, LLC, Asset Insight Technologies, LLC, 7127 Concord Place,
Highlands Ranch, CO 80130 (Colorado Department of Transportation –
Research, 4201 E. Arkansas Ave., Denver, CO 80222) (Apr 2006) There does
not appear to be a compelling reason to use a particular ice control chemical in
fixed automated spray technology installation.
PAVE/ Evaluation of Effects of Tire Size and Inflation Pressure on Tire Contact 17-18
tire Stresses and Pavement Response by Emmanuel G. Fernando, Dilip Musani,
impact Dae-Wook Park, and Wenting Liu, Texas Transportation Institute, Texas A&M
University System, College Station, Texas 77843-3135 (Texas Department of
Transportation, Research and Technology Implementation Office P.O. Box
5080, Austin, Texas 78763-5080; 979.845.1734; http://tti.tamu.edu) (Aug 2006)
The effects of differences in tire contact pressure distributions are mainly seen
near the surface and diminish with depth.
PAVE/ Investigation of Spall Repair Materials for Concrete Pavement by Serena M. 19-20
spall Markey, Sang Ick Lee, Anal K. Mukhopadhyay, Dan G. Zollinger David P.
repair Whitney and David W. Fowler, Texas Transportation Institute, Texas A&M
University System, College Station, Texas 77843-3135 (Texas Department of
Transportation, Research and Technology Implementation Office P.O. Box
5080, Austin, Texas 78763-5080; 979.845.1734; http://tti.tamu.edu) (May
2006) Spall repair materials to be applied in fields should be selected through
the consideration and comparison of material acceptability and properties.
PAVE/ Mechanistic Model to Predict the Impact of the Aggregate Matrix on the 21-22
asphalt Permanent Deformation of Asphalt Mixtures by Samer Dessouky, Eyad
Masad, and Dallas Little, Texas Transportation Institute, Texas A&M
University System, College Station, Texas 77843-3135 (Texas Department of
Transportation, Research and Technology Implementation Office P.O. Box
5080, Austin, Texas 78763-5080; 979.845.1734; http://tti.tamu.edu) (Jul 2005)
This study focused on the development of continuum models for hot mix
asphalt (HMA) that account for the influence of microstructure distribution into
macroscopic behavior.
PAVE/ New Technologies for Evaluating Flexible Pavement Construction: Year 1 23-24
TECH Report by Stephen Sebesta, Cindy Estakhri, Tom Scullion, and Wenting Liu,
Texas Transportation Institute, Texas A&M University System, College
Station, Texas 77843-3135 (Texas Department of Transportation, Research and
Technology Implementation Office P.O. Box 5080, Austin, Texas 78763-5080;
979.845.1734; http://tti.tamu.edu) (Jun 2006) This project focuses on evaluating
new technologies that can characterize mechanistic properties in the field.
PAVE/ Performance of Colorado’s First Rubblization Project on I-76 Near Sterling 25-26
rubbliza- by Robert Laforce, Yeh and Associates, 5700 E. Evans Ave., Denver, CO
tion 80222 (Colorado Department of Transportation – Research, 4201 E. Arkansas
Ave., Denver, CO 80222) (Jan 2006) Rubblization provides a cost-competitive
tool in the rehabilitation of old concrete pavements.
PLAN/ Are Highways Subsidized? in The Freeman by Randal O‘Toole (Foundation 27-28
FIN for Economic Education, 30 South Broadway, Irvington-on-Hudson, New
York, 10533; 1-800-960-4FEE; http://www.fee.org/publications/the-
freeman/article.asp?aid=6601) (Nov 2006) User fees cover nearly 90% of the
total amount spent on highways.
PLAN/ Parking Spaces/Community Places: Finding the Balance through Smart 29-30
Smart Growth Solutions (Development, Community, and Environment Division, U.S.
Growth Environmental Protection Agency, Washington, DC 20460) (Jan 2006) Parking
requirements should be altered to allow a better measure of the true demand for
parking and to balance parking with other community goals.
6
SAFE/ Improving Pedestrian Safety at Unsignalized Crossings, NCHRP Report 562 31-32
pedes- by Kay Fitzpatrick, et al. (Transportation Research Board, 500 Fifth Street,
trian NW, Washington, DC 20001; (202) 334-3213; http://gulliver.trb.org/bookstore)
(2006) A proposed new pedestrian warrant is that the number of pedestrians
waiting to cross a street should be no greater than the number of vehicles
waiting to cross or enter a street.
SAFE/ Underinflated Tires in the United States (United States Government 33-34
tires Accountability Office, 441 G Street NW, Room LM, Washington, D.C. 20548;
http://www.gao.gov/new.items/d07246r.pdf) (February 9, 2007) Filing tires
with nitrogen would reduce leakage.
STR/ Bridge Rating Practices and Policies for Overweight Vehicles, NCHRP 35-36
bridge Synthesis 359 by Gongkang Fu and Clementine Fu, Troy, Michigan
(Transportation Research Board, 500 Fifth Street, NW, Washington, DC 20001;
(202) 334-3213; http://gulliver.trb.org/bookstore) (2006) The multi-state permit
programs of the New England Transportation Consortium and SASHTO
represent a successful model for improved uniformity in oversize/overweight
permitting.
STR/ Design and Construction Guidelines for Geosynthetic-Reinforced Soil Bridge 37-38
bridge Abutments with a Flexible Facing, NCHRP Report 556 by Jonathan T. H. Wu,
abutment Kevin Z. Z. Lee, Sam B. Helwany, Kanop Ketchart, University of Colorado at
Denver (Transportation Research Board, 500 Fifth Street, NW, Washington,
DC 20001; (202) 334-3213; http://gulliver.trb.org/bookstore) (2006) A design
method and construction guidelines for geosynthetic reinforced soil (GRS)
abutments with a flexible facing have been developed.
STR/ Development of LRFD Specifications for Horizontally Curved Steel Girder 39-40
curved Bridges, NCHRP Report 563 by John Kulicki, Wagdy Wassef, Danielle
bridge Kleinhans, Chaih Yoo, Andrzej Nowak, Mike Grubb (Transportation Research
Board, 500 Fifth Street, NW, Washington, DC 20001; (202) 334-3213;
http://gulliver.trb.org/bookstore) (2006) The two design examples are available
on the AASHTO website.
TRAN/ Transit Agency Participation in Medicaid Transportation Programs, TCRP 41-42
welfare Synthesis 65 by Kenneth L Hosen and Elisabeth Fetting, KFH Group, Inc.,
Bethesda, Maryland (Transportation Research Board, 500 Fifth Street, NW,
Washington, DC 20001; (202) 334-3213; http://gulliver.trb.org/bookstore)
(2006) This review is conducted to assist transit agencies in exploring
opportunities to coordinate services with NEMT programs.
7
TRF/ Evaluation of the Clearview Font for Negative Contrast Traffic Signs by 43-44
signs Andrew J. Holick, Susan T. Chrysler, Eun Sug Park, and Paul J. Carlson, Texas
Transportation Institute, Texas A&M University System, College Station,
Texas 77843-3135 (Texas Department of Transportation, Research and
Technology Implementation Office P.O. Box 5080, Austin, Texas 78763-5080;
979.845.1734; http://tti.tamu.edu) (Apr 2006) Clearview font is inferior to the
current FHWA font.
TRF/ Motorist Comprehension of Traffic Control Devices for Mobile Operations by 45-46
mobile Melisa D. Finley, Brooke R. Ullman, and Nada D. Trout in Transportation
signs Research Record 1948 (Transportation Research Board, 500 Fifth Street, NW,
Washington, DC 20001; (202) 334-3213; http://gulliver.trb.org/bookstore)
(2006) Drivers frequently misunderstand mobile sign information.
TRF/ Traffic Congestion in North Carolina: Status, Prospects and Solutions by 47-48
congest- David T. Hartgen, Professor of Transportation Studies, University of North
ion Carolina at Charlotte, dthartge@email.uncc.edu (John Locke Foundation, 200
W. Morgan, Suite 200, Raleigh NC 27601; Info@johnlocke.org;
http://www.johnlocke.org/site-docs/traffic/TrafficCongestion.pdf) (Mar 2007)
Instead of saying that transit programs should get 20-50% of funds, modes of
transportation should get funds in proportion to their demand.
8
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Performance of a Pile-Supported Embankment by Edward J. Hoppe and Stanley L. Hite, Virginia
Transportation Research Council, 530 Edgemont Road, Charlottesville, VA 22903 (Virginia
Department of Transportation, 1401 E. Broad Street, Richmond, VA 23219) (Jun 2006)
Highlights kind built in Virginia. Consequently, the
Construction of pile-supported Virginia Transportation Research Council
embankments typically does not require (VTRC) was asked to perform a field
specialty equipment or methods. assessment and provide feedback for similar
Significant savings can be achieved on pile- ground improvement projects that may be
supported embankment projects because of planned by VDOT in the future.
the relatively high material costs involved in The purpose of this study was to
this type of construction. evaluate the field performance of a pile-
supported embankment constructed over the
In 2004, the Virginia Department of eastern approach (King and Queen County) to
Transportation (VDOT) initiated corridor the new bridge over the Mattaponi River
improvements along Route 33 in and around (replacing the existing Lord Delaware Bridge).
the Town of West Point. The project starts at F The scope of work included field
Street in West Point and ends at Ashby Road in instrumentation and data gathering as related to
King and Queen County. It comprises three stress transfer and settlement. The objective
road sections and two bridges, one over the was to measure actual soil pressures that are
West Point Creek and the other over the exerted at the geotextile fabric bridging pile
Mattaponi River. caps and to measure stresses acting over pile
Marginal soil conditions presented caps. In addition, data analysis was to be
significant construction challenges. The site is carried out to provide information that VDOT
located in a marshy area, underlain by very soft engineers could use to optimize future designs
deposits of normally consolidated marine clays. of pile-supported embankments.
It is technically difficult to construct an
embankment over a soil that has a very low Conclusions
bearing capacity and that is prone to relatively Construction of pile-supported
large settlements. Failure often occurs when the embankments typically does not require
underlying foundation soil cannot support the specialty equipment or methods. No significant
weight of a new embankment. To address this construction problems were reported by the
problem, various ground stabilization general contractor working on the West Point
techniques, including wick drains and pile- project.
supported embankment, were specified along A rapid increase in the bearing capacity
some sections of the proposed roadway. was observed during construction.
Pile-supported embankments have not Field monitoring confirmed the
been constructed by VDOT in the past, partly mechanism of soil arching, which develops in
because of the additional costs involved. The the embankment material, between columns.
embankment at West Point is the first one of its
9
Numerical analysis indicated that Benefits and Costs Assessment
stiffness and strength of the upper foundation With the use of the recently developed
soil layers have a dominant effect on the stress GeogridBridge analysis worksheet, the results
transfer and embankment settlement. indicate that it may be possible to realize
The cost-effectiveness of pile-supported substantial cost savings on projects similar in
embankments depends on accurate material scope to the one constructed at West Point
characterization and rational analytical Potential cost savings are illustrated as
procedures. follows:
Case 1: Retain the 7 ft column spacing,
Recommendations but do not use any high-strength geosynthetic
VDOT‘s Materials Division should fabric. The West Point project used 20,893
evaluate the feasibility of pile-supported square yards of fabric at a cost of $97,780. It
embankments at locations where the speed of appears that it may have been possible to
construction is critical. construct the embankment without any
VDOT‘s Materials Division should geosynthetic reinforcement.
carry out detailed subsurface investigations, Case 2: Increase the column spacing to
including in-situ strength and deformation 8.5 ft, and use a single layer of high-strength
testing, at all sites where pile-supported geosynthetic fabric. The West Point project
embankments are considered. . used 508 piles and pile caps, at a combined cost
VDOT‘s Materials Division should of $702,910. Increasing the pile spacing from 7
develop in-house geotechnical expertise in the to 8.5 ft would require approximately 30
analysis and design of pile and other columnar percent less piles and pile caps. Combined with
reinforcement for highway embankments. the use of a single layer of high-strength
VTRC should monitor the field geosynthetic fabric, the resulting cost savings
performance of columnar reinforcement would be about $250,000.
projects to provide feedback for future designs. Significant savings can be achieved on
pile-supported embankment projects because of
the relatively high material costs involved in
this type of construction.
10
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Stability of Column-Supported Embankments by George M. Filz and Michael P. Navin, Virginia
Transportation Research Council, 530 Edgemont Road, Charlottesville, VA 22903 (Virginia
Department of Transportation, 1401 E. Broad Street, Richmond, VA 23219) (Jun 2006)
Highlights slope stability are needed to capture the
Numerical analyses of slope stability are realistic failure modes that can control
needed to capture the realistic failure modes embankment performance and for which there
that can control embankment performance. is no practical alternative at present.
Reliability analyses are a necessary A related benefit of numerical analyses
component of design for embankments is that, if properly performed, they also capture
supported on columns. the potential for block sliding and bearing
capacity failure. Current practice is to perform
The primary purpose of this research separate analyses for these failure modes using
was to develop reliable procedures that approximate analytical models. With properly
geotechnical engineers can use to analyze the conducted and well-interpreted numerical
stability of column-supported embankments. analyses, a single analysis method can address
Existing procedures are available for analysis all these aspects of system performance. In
of the stability of embankments supported on order to properly perform such analyses,
piles and stone columns, and these are special care must be devoted to idealization of
presented in the appendices. Reliability-based soil stratigraphy, soil material characterization,
approaches were developed for stability and numerical modeling details.
analysis of embankments supported on columns This research also shows that reliability
installed by the deep mixing method. Deep- analyses are a necessary component of design
mixed materials are variable, and this has an for embankments supported on columns
important impact on the procedures that should installed by the deep mixing method. The
be used to produce reliable designs. The strength of deep-mixed materials is quite
stability analysis methods presented here for variable, and reliability analyses permit this
embankments on deep-mixing-method columns variability to be rationally incorporated in the
are expected to also apply to vibro-concrete design process. Furthermore, these systems are
columns. complex, and typical variations in clay
This research shows that failure strength, if not accounted for, could induce
mechanisms like column tilting and bending abrupt bending failure in isolated columns.
can cause embankment failure at lower load Consequently, the ordinary values of factor of
levels than would induce composite shearing safety that geotechnical engineers use to
through the columns and soft ground. Limit develop reliable designs for other embankment
equilibrium methods, as currently employed in systems are not applicable to embankments
engineering‘ practice, do not capture tilting and supported on columns installed by the deep
bending failure modes, and they are not safe for mixing method. For instance, an example
analysis of embankments supported on strong embankment supported on isolated columns
columns. For this reason, numerical analyses of was analyzed and found to have a factor of
11
safety equal to 1.4. This value would be The value of E50/qu is about 300 for
considered acceptable in many other situations, soil-cement mixtures created by the wet
but reliability analyses using the Direct method using either single or multiple augers.
Integration Method and the Hasofer-Lind Limit equilibrium analyses do not
Method showed that the example embankment reflect important potential failure mechanisms,
has a probability of failure equal to about 3%, such as column tilting and bending. These
which is excessively high for public failure mechanisms are captured in properly
transportation applications. This result conducted numerical analyses.
demonstrates that typical values of the factor of The numerical analysis procedures
safety are not adequate for judging recommended here have been successfully
acceptability of these systems, and reliability verified against the I-95/Route 1 case history
analyses are needed. and two sets of centrifuge model tests.
Another benefit of reliability analyses is For embankments supported on deep-
that the coefficient of variation used to design mixing-method columns, two-dimensional
the embankments can also be used to write a analyses produce about the same lateral
statistically based specification. Such deflections as three-dimensional analyses at the
specifications have great potential to reduce same area replacement ratio and the same
construction disputes because they avoid column modulus.
specification of unrealistically high minimum Numerical analyses demonstrate the
strengths while still fully meeting the design substantial beneficial effects on stability of
intent. continuous panels compared to isolated
The numerical and reliability analysis columns beneath the side slopes of
procedures discussed in this report were embankments.
applied to deep-mixing-method columns, but Values of factor of safety that are
the procedures should also be relevant and typically used for design of embankments on
applicable to vibro-concrete columns, which, unimproved ground, e.g., about 1.4 to 1.5, are
like deep-mixing-method columns, have the too small for embankments supported on deep-
characteristics of being much stronger than the mixing method columns when mean parameter
surrounding soil and having low tensile values are used in the analyses.
capacity. Reliability analyses are needed to
rationally account for (1) the significant
Conclusions variability of deep-mixed materials and (2) the
The coefficient of variation of impact that other changes in system parameters
unconfined compressive strength for 13 data have on the abrupt tensile failure that can occur
sets from nine deep mixing projects in the U.S. in deep-mixed materials.
ranges from 0.34 to 0.79 and has an average The Hasofer-Lind Method was found to
value of about 0.57. After removing the be more accurate than either the Taylor Series
variation due to controllable trends of age and or Point Estimate Methods of reliability
water-to-cement ratio of the slurry, the analysis.
coefficient of variation ranges from 0.17 to Reliability-based design permits
0.67 and has an average value of about 0.4. rational development of statistically based
The autocorrelation distance ranged specifications, which are expected to reduce
from 40 to 60 ft for three wet-mixing-method contract administration problems.
projects.
12
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Tires and Passenger Vehicle Fuel Economy by Committee for the National Tire Efficiency Study
(Transportation Research Board, 500 Fifth Street, NW, Washington, DC 20001; (202) 334-3213;
http://gulliver.trb.org/bookstore) (2006)
Highlights national security to improving local air quality
A 10% reduction in tire rolling resistance and reducing greenhouse gas emissions.
promises a 1 to 2% increase in the fuel Maximizing the wear life of tires is also
economy of these vehicles. important from the public standpoint of
A 1 to 2% increase in fuel economy would controlling the population of scrap tires that can
save up to 2 billion gallons of fuel per year. burden landfills and recycling programs. While
This fuel savings is equivalent to taking up the handling, traction, and other operating
to 4 million vehicles off the road. characteristics of tires are of particular interest
to tire buyers, they are also matters of broader
Tires affect vehicle fuel economy public interest inasmuch as they may influence
mainly through rolling resistance. As a tire rolls the safety performance of vehicles on the
under the vehicle‘s weight, its shape changes nation‘s highways.
repeatedly as it experiences recurring cycles of This study examines the rolling
deformation and recovery. In the process, resistance characteristics of passenger tires sold
mechanical energy otherwise available to turn for replacement and how differences in rolling
the wheels is converted into heat and dissipated resistance relate to other tire attributes.
from the tire. More fuel must be expended to Congress asked the National Research Council
replace this lost energy. Combinations of (NRC) to assess the feasibility of reducing
differences in tire dimensions, design, rolling resistance in replacement tires and the
materials, and construction features will cause effects of doing so on vehicle fuel
tires to differ in rolling resistance as well as in consumption, tire wear life and scrap tire
many other attributes such as traction, generation, and tire operating performance as it
handling, noise, wear resistance, and relates to motor vehicle safety.
appearance. Once they are placed in service, Reducing the average rolling resistance
tires must be properly maintained to perform as of replacement tires by a magnitude of 10% is
intended with respect to all attributes. The technically and economically feasible. A
maintenance of proper inflation pressure is reduction in the average rolling resistance of
especially important. replacement tires in the fleet can occur through
The collective outcomes of the choices various means. Consumers could purchase
consumers make when they buy tires are more tires that are now available with lower
matters of public interest. The 220 million rolling resistance, tire designs could be
passenger cars and light trucks in the United modified, and new tire technologies that offer
States consume about 130 billion gallons of reduced rolling resistance could be introduced.
motor fuel annually. Finding ways to reduce More vigilant maintenance of tire inflation
this energy consumption is a national goal for pressure will further this outcome.
reasons ranging from ensuring economic and
13
Rolling resistance varies widely among without adverse effects on tire wear life and
replacement tires already on the market, even scrap tire populations.
among tires that are comparable in price, size, Although traction may be affected by
traction, speed rating, and wear resistance. modifying a tire‘s tread to reduce rolling
Consumers, if sufficiently informed and resistance, the safety consequences are
interested, could bring about a reduction in probably undetectable. Changes are routinely
average rolling resistance by adjusting their tire made in tire designs, materials, and
purchases and by taking proper care of their construction methods for reasons ranging from
tires once in service, especially by maintaining noise mitigation and ride comfort to steering
recommended inflation pressure. response and styling. All can have implications
Tires and their rolling resistance for other tire properties and operating
characteristics can have a meaningful effect on performance, including traction capability.
vehicle fuel economy and consumption. A 10% Discerning the safety implications of small
reduction in average rolling resistance promises changes in tire traction characteristics
a 1 to 2% increase in the fuel economy of these associated with tread modifications to reduce
vehicles. A 1 to 2% increase in fuel economy rolling resistance may not be practical or even
would save about 1 billion to 2 billion gallons possible.
of fuel per year. This fuel savings is equivalent Reducing the average rolling resistance
to the fuel saved by taking 2 million to 4 of replacement tires promises fuel savings to
million vehicles off the road. consumers that exceed associated tire purchase
The effects of reductions in rolling costs, as long as tire wear life is not shortened.
resistance on tire wear life and scrap tires are A 10% reduction in rolling resistance can
difficult to estimate because of the various reduce consumer fuel expenditures by 1 to 2
ways by which rolling resistance can be percent for typical vehicles. This savings is
reduced. The tread is the main factor in tire equivalent to 6 to 12 gallons per year, or $12 to
wear life and the main component of the tire $24 if fuel is priced at $2 per gallon. Tire
contributing to rolling resistance. Reductions in technologies available today to reduce rolling
tread thickness, volume, and mass are among resistance would cause consumers to spend
the means available to reduce rolling resistance, slightly more when they buy replacement tires,
but they may be undesirable if they lead to on the order of 1 to 2% or an average of $1 to
shorter tire lives and larger numbers of scrap $2 more in tire expenditures per year. These
tires. Various tread-based technologies are technologies, however, may need to be
being developed and used with the goal of accompanied by other changes in tire materials
reducing rolling resistance without significant and designs to maintain the levels of wear
effects on wear resistance. The practical effects resistance that consumers demand. While the
of these technologies on tread wear and other effect of such accompanying changes on tire
tire performance characteristics have not been production costs and prices is unclear, the
established quantitatively. However, continuing overall magnitude of the fuel savings suggests
advances in tire technology hold much promise that consumers would likely incur a net savings
that rolling resistance can be reduced further in their combined fuel and tire expenditures.
14
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
A Synthesis to Improve the Design and Construction of Colorado’s Bridge Anti-Icing Systems by
Gordon T. Bell, Wilfrid A. Nixon, Robert D. Stowe, Bell Enterprises, LLC, Asset Insight
Technologies, LLC, 7127 Concord Place, Highlands Ranch, CO 80130 (Colorado Department of
Transportation – Research, 4201 E. Arkansas Ave., Denver, CO 80222) (Apr 2006)
Highlights Given this, CDOT will need to establish long
FAST installations are not ―off the shelf‖ or term relationships with vendors to ensure that
―plug and play.‖ their FAST installations function as intended
There does not appear to be a compelling and for the period of time intended. The
reason to use a particular ice control installation of a FAST system is an ongoing
chemical in FAST installation. commitment, not a one-time event. A particular
A more aggressive preventive maintenance aspect of concern in this regard is the
program should be developed. automated operation of such systems. There are
clearly significant challenges in achieving fully
This study has reviewed the literature automated operation of a FAST installation,
pertaining to fixed automated spray technology and the information reviewed in this study
(FAST) installations, including a number of strongly indicates that those challenges have
studies that report on the successes and failures not yet been met. Accordingly, if such
of these installations, and made specific automated performance is a requirement for a
recommendations for their improvement. In given site, there should be an expectation of
addition, the study included a survey of significant work in the deployment phase to
agencies who currently use such systems, and achieve full functionality.
of the vendors who make and sell such systems. On the basis of the feedback received
Finally, a number of interviews of Colorado through the various survey instruments and
Department of Transportation (CDOT) interviews, there does not appear to be a
personnel have been made, with the specific compelling reason to use a particular ice
intent of determining what has and has not control chemical in FAST installation. A
worked in their experience with FAST perceived wisdom had been that potassium
installations. On the basis of this, the study has acetate should be used to avoid problems with
led to the preparation of a model specification corrosion, but experience with other chemicals
for such systems, together with four specific indicates that, if suitable care is taken to keep
observations. equipment clean, corrosion is not an issue.
Accordingly, the chemical used in a given
Conclusions installation should be chosen primarily on the
It is clear from all the experience with basis of its ability to perform over the likely
FAST installations that these are in no way to range of road temperatures to be experienced
be considered ―off the shelf‖ or ―plug and play‖ during precipitation or frost events at that
systems. Each site has unique characteristics, location.
and presents unique challenges to achieving A common feature of the majority of
long-term success with these installations. FAST sites was that preventive maintenance
15
was not conducted, apart from an annual structural considerations, architectural
draining and flushing of the system at the start consultant for architectural considerations, etc.
of the summer. A more aggressive preventive
maintenance program should be developed for Recommendations
each FAST installation, and actions taken under Staff Maintenance should hire
this program should be carefully documented consultants to verify/expand portions of
and archived. It is evident by the information in Guideline Criteria that need amplification or
this report that CDOT should undertake an insertion of maintenance preferences and create
aggressive position in developing and a standard Anti-Icing Project Special Provision
supporting, with ―in-house‖ and vendor (architectural, structural, electrical, mechanical,
expertise, a preventative maintenance program environmental, instrumentation).
for existing and future FAST sites. Staff Maintenance should hire
A major concern expressed in consultants to develop a design/build
interviews was the difficulty of working with specification for designs, which are different
underground storage facilities. Accordingly it is for completely belowground and completely
recommended that all facilities should be aboveground.
aboveground. The implementation of these Staff Maintenance should develop
conclusions and recommendations, together minimum CDOT requirements for
with the use of the model specification will aboveground installation, i.e., dimensions of
result in a much more efficient and effective building (height, width, depth), door
installation and operation of FAST systems in requirements (double doors, rolling doors, etc.).
the State of Colorado. Staff Maintenance should hire
During the informational meetings with consultants to verify requirements for
CDOT personnel, it was discovered that Staff underground installation drawings (mechanical,
Bridge had major involvement in the revision architectural, electrical, environmental).
of the anti-icing specification currently in use Staff Maintenance should develop a
by CDOT. Staff Maintenance is the primary procedure/checklist for selecting and designing
user and maintainer of these systems and has Anti Icing units, for example:
greater knowledge and experience with the Is anti-icing required?
RWIS and other required components of the Will installation be standard
system. Accordingly it is recommended that aboveground or belowground?
Staff Maintenance should have primary control Will standard specification work on this
of this specification and its revisions. They installation?
should seek necessary assistance and expertise Is in-house expertise available and
for the implementation of the final timely or will design/installation be
specification, e.g., structural consultant for completely per design/build contract?‖
16
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Evaluation of Effects of Tire Size and Inflation Pressure on Tire Contact Stresses and Pavement
Response by Emmanuel G. Fernando, Dilip Musani, Dae-Wook Park, and Wenting Liu, Texas
Transportation Institute, Texas A&M University System, College Station, Texas 77843-3135
(Texas Department of Transportation, Research and Technology Implementation Office P.O. Box
5080, Austin, Texas 78763-5080; 979.845.1734; http://tti.tamu.edu) (Aug 2006)
Highlights inflation pressure. For this evaluation,
The effects of differences in tire contact researchers used the tire imprints taken during
pressure distributions are mainly seen near testing to determine tire contact areas for the
the surface and diminish with depth. range of tire loads and tire inflation pressures at
Tire View software will provide useful data which the different tires were tested.
for pavement design applications. Researchers observed that the contact area
decreases with increasing inflation pressure and
This research investigated existing increases with increasing tire load based on
procedures for predicting pavement response to trend lines fitted to the data. In addition, the
applied surface tractions at the tire-pavement measured contact areas for various inflation
interface. The objective was to establish how pressures plot almost parallel for different
tire contact stresses may be modeled in existing levels of tire load, indicating a negligible
layered elastic programs to better approximate interaction effect between tire load and
the effects of non-uniform tire contact stresses inflation pressure. From this analysis, the
and account for differences in tire construction, effects of tire load and tire inflation pressure
tire load and tire inflation pressure on predicted were found to be statistically significant.
pavement response. Researchers constructed and used a 3D
finite element model of asphalt concrete
Findings pavements to compare predictions of pavement
For the tires tested in this project, response based on measured tire contact
researchers found the data from all replicate stresses with corresponding results obtained
runs to be highly repeatable for each using layered linear elastic analyses. For a
combination of tire load and tire inflation uniform circular pressure distribution,
pressure included in the test matrices for both researchers found that the predicted strains with
tires. The data from tests conducted on the depth from the 3D FE analysis using ABAQUS
295/75R22.5 and 11R22.5 radials generally are quite comparable with the corresponding
show excellent to good repeatability except for predictions from BISAR.
a few cases where only two out of the three In terms of the predicted service life
replicates were found to be repeatable. based on sub grade compressive strain, the
Replicate runs from the bias-ply and wide-base results show no significant differences between
radial tires showed the least repeatability the 3D finite element and layered elastic (BM
among the tires tested. and BC) analyses. This finding indicates that
Researchers investigated relationships the effects of differences in tire contact
between tire contact area, tire load and tire pressure distributions are mainly seen near the
17
surface and diminish with depth. Thus, in terms and layered elastic analysis methods, the
of the effect of tire contact stresses on authors recommend the application of the BM
pavement rutting, the permanent deformation method in the layered elastic analysis of
properties of the surface material would be pavement response. These calculations may be
critical. done using the Tire View program developed
The differences between the predicted during this project In this way, differences in
fatigue lives from the 3D FE and modified tire footprints can be considered in the layered
layered elastic (BM) analyses are not elastic analysis.
statistically significant. However, the In addition, Tire View provides
differences in the fatigue predictions between estimates of tire contact stress distributions for
the 3D FE and BC analyses were found to be a given tire type, tire load and tire inflation
significant. pressure based on polynomial interpolations of
Differences in the fatigue predictions the measured values stored in the data base.
between the BM and BC methods showed the Pavement engineers may use these estimates in
effect of tire contact area in the predicted AC a 3D finite element program to predict
tensile strains. For a given tire load and tire pavement response for applications where a
inflation pressure, the conventional method of rigorous analysis is warranted or desired.
analysis ignores the differences in the tire Researchers note that the predictions are
footprints between various tire types. specific to the tires tested. Since differences in
It was observed that differences in the tire construction will affect tire contact
MC values between the 3D FE and layered pressures, the predicted tire contact stress
elastic analyses are greatest near the surface distributions are tied to the database on which
and diminish quite rapidly with depth. In the interpolations were made. In addition, the
general, researchers observed that for the cases predictions are limited to the range of the
investigated, the differences were largest within available data. For cases outside this range,
the top 2 inches of the surface layer. Within the researchers recommend that tests be conducted
base and subgrade, the differences are not to measure tire contact stresses for the variables
considered significant. of interest.
The critical MC yield function values Notwithstanding these constraints,
occurred near the top and bottom of the AC researchers consider the establishment of the
layer for the cases considered. At these depths, database and the development of Tire View to
researchers examined the differences between be significant outcomes of this project The
the 3D FE and layered elastic procedures. It authors are of the opinion that Tire View will
was found that the differences between the provide useful data for pavement design
predicted MC values from the 3D FE and BM applications, particularly for establishing or
analyses are not statistically significant. verifying design requirements for pavements
However, the differences in the predicted MC subjected to heavy truck traffic, through
values between the 3D FE and BC analyses are comparative analyses of the effects of different
significant. tires and differences in wheel load assumptions
Based on the findings from the on predicted pavement response and
comparative evaluation of 3D finite element performance.
18
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Investigation of Spall Repair Materials for Concrete Pavement by Serena M. Markey, Sang Ick
Lee, Anal K. Mukhopadhyay, Dan G. Zollinger David P. Whitney and David W. Fowler, Texas
Transportation Institute, Texas A&M University System, College Station, Texas 77843-3135
(Texas Department of Transportation, Research and Technology Implementation Office P.O. Box
5080, Austin, Texas 78763-5080; 979.845.1734; http://tti.tamu.edu) (May 2006)
Highlights modulus had a comparatively low CoTE value.
Rigid materials had the highest values of Shrinkage values were highly variable due to
elastic modulus, and flexible materials had the wide range of material types and the
the lowest values. amount of temperature change experienced
Rigid materials experienced lower shrinkage while curing, but rigid materials experienced
values. lower shrinkage values while semi-rigid and
Spall repair materials to be applied in fields flexible materials experienced high shrinkage
should be selected through the consideration values.
and comparison of material acceptability Thermal cycling of simulated spalls
and properties. produced no degradation of the repair
materials. Tests for tensile bond values were
While testing the mechanical properties taken from each of the repairs after cycling but
of each material, it was found that the different results were variable partially due to the nature
repair materials had very different stiffnesses. of the test and the varying bond surface.
Accordingly the repair materials were grouped Certain types of rigid as well as flexible
into three categories; rigid, semi-rigid, and materials were found to bond well. Abrasion
flexible with magnesium phosphates tests for durability showed that all of the
representing the more rigid materials, and the polymeric materials performed well.
polymer concretes representing the more Materials from successful repairs in the
flexible materials. Ultimate compressive field were cored and tensile bond strengths
strengths could only be tested for rigid compared to core prepared in the lab. It was
materials, and flexural strength could only be found that bond strengths from field specimens
obtained from the rigid and semi-rigid were lower than laboratory specimens, but
materials. because of the very limited number of field
Modulus of elasticity, shrinkage, and cores obtained, results are less than definitive.
coefficient of thermal expansion (CoTE) were Additionally, cylinders were obtained from
the compatibility properties tested for each field placement of material in Ft. Worth.
material. It was found that rigid materials like Compression and elastic modulus tests were
the magnesium phosphates had the highest taken after 7 days and compared. In general it
values of elastic modulus, and flexible was found that specimens created in the lab had
materials like the polymer concretes had the higher compressive strength and elastic
lowest values. In general materials with a low modulus values than those created in the field.
elastic modulus had a comparatively high Spall repair materials to be applied in
CoTE value, while materials with a high elastic fields should be selected through the
19
consideration and comparison of material consideration for future overlay operations and
acceptability and properties. The acceptability the ability of the spall repair material to bond to
of material is determined based on whether the the overlay itself. The lower modulus repair
bond strength of a material satisfies the material will not bond well to a concrete
engineers‘ specified bond strength. Also, the overlay, which should be given due
materials can be ranked according to the consideration in this regard in the material
following criteria derived from material selection process. The list of ranked materials
properties: material cost, placeability, and is used to recommend appropriate repair
overall utility. Overall utility includes material.
20
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Mechanistic Model to Predict the Impact of the Aggregate Matrix on the Permanent Deformation
of Asphalt Mixtures by Samer Dessouky, Eyad Masad, and Dallas Little, Texas Transportation
Institute, Texas A&M University System, College Station, Texas 77843-3135 (Texas Department of
Transportation, Research and Technology Implementation Office P.O. Box 5080, Austin, Texas
78763-5080; 979.845.1734; http://tti.tamu.edu) (Jul 2005)
This study developed… the vicinity of a point on the mechanical
an elasticity gradient model that employs the response of that point. FE results showed that
strain gradient concept and effective the developed model was successful in
material properties overcoming some limitations of using the
an elasto-visco-plastic continuum model to individual properties of the constituents‘ in FE
predict HMA response and performance analysis of HMA microstructure. For example
under wheel loadings the model reduced mesh size dependency,
reduced sensitivity of the response to small
This study focused on the development changes in the microstructure caused by image
of continuum models for hot mix asphalt capturing and processing, and reduced the
(HMA) that account for the influence of numerical instability caused by several orders
microstructure distribution into macroscopic of magnitude indifference in stiffness between
behavior. The first advancement in this study adjacent elements of the microstructure. In
was the development of an elasticity gradient addition, the model captured the influence of
model that employs the strain gradient concept HMA length scales on microscopic and
and effective material properties. The use of macroscopic responses. The results showed that
strain gradient introduces a length scale the determined HMA effective properties using
parameter to the elasticity constitutive model, the model were more consistent with the
which allows the model to capture the influence experimental measurements.
of particle size distribution on HMA response. The second advancement in this study
Analytical procedures were developed in this was the development of an elasto-visco-plastic
study to obtain microstructure characteristic continuum model to predict HMA response and
length scales to be used in the constitutive performance under wheel loadings. The model
relationship. These analytical procedures are included microstructure parameters that
the moving window technique and the captured the directional distribution of
autocorrelation function. aggregates and density of cracks. In addition,
The elasticity gradient model was the model was capable to account for the
implemented in finite element (FE) analysis factors affecting the mechanisms of permanent
and used to analyze microstructure response deformation such as shear stress, aggregate
and predict the macroscopic properties for structure friction and dilation, confining
HMA with different aggregate characteristics pressure, strain rate, and stress path direction.
and structures. In FE analysis, each point was The elasto-visco-plastic model was
assigned effective local material properties, implemented in FE analysis. The
which capture the influence of the material in implementation of the model was in the form of
21
a fully implicit algorithm using the backward mixes were used in this study to determine
Euler scheme in time-step control. The model parameters and evolution formulation
Newton-Raphson iterative scheme was used to for each mix type. Strength tests were
define available initial solutions. The numerical conducted at different loading rates and
scheme is based on the return mapping confining pressures. Model parameters were
algorithm, which leads to elastic predictor- determined using a systematic approach by
plastic corrector steps. The algorithm included using the stress-strain relationship.
a consistency condition analogous to the time- Experimental results showed that granite had
independent plasticity theory to evaluate the the lowest potential for permanent deformation,
visco-plastic multiplier. Quadratic convergence the highest work hardening capability. Gravel
was achieved in the analysis by using had the highest potential for permanent
algorithmic elasto-visco-plastic tangent moduli deformation, and limestone had the highest
in the algorithm. dilation.
A parametric analysis was conducted to FE analysis was conducted to simulate
investigate the effect of key parameters in the experimental measurements under compression
model on the material response. The results and extension loading with different strain rates
showed clearly that the model is sensitive to and confining pressures. The FE results
particle friction (ά), material hardening (κ), indicated that the elasto-visco-plastic model
dilation (β), anisotropy (Δ), void nucleation and parameters were able to distinguish between
growth (ξ), and stress path direction (d). d HMA mixtures with different aggregate
affects the geometry of the yield surface in the characteristics. The simulation results showed
deviatoric plane. d = 0.778 is the minimum that tensile strength of the mixes is much lower
value to achieve the convexity of the yield than compressive strength. The damage
surface. An increase in the anisotropy level parameters used in simulating the extension
causes an increase in the material strength in tests are different than those used in the
the axial direction normal to the preferred compression tests, because softening in
orientation of particles. The yield strength in extension test occurs earlier and at a faster rate
the direction parallel to the orientation of than in compression.
particles decreases slightly with an increase in FE analysis was also utilized to
anisotropy level. The study also showed that simulate permanent deformation in a pavement
loading rate and confinement affected the section. Anisotropy is found to influence shear
model response. Increasing loading rate and stress distribution, permanent deformation
confinement caused an increase in the ultimate underneath the tires, and dilation in the lateral
stress. direction and beneath the tires.
Triaxial compression and extension
strength tests on granite, gravel, and limestone
22
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
New Technologies for Evaluating Flexible Pavement Construction: Year 1 Report by Stephen
Sebesta, Cindy Estakhri, Tom Scullion, and Wenting Liu, Texas Transportation Institute, Texas
A&M University System, College Station, Texas 77843-3135 (Texas Department of Transportation,
Research and Technology Implementation Office P.O. Box 5080, Austin, Texas 78763-5080;
979.845.1734; http://tti.tamu.edu) (Jun 2006)
Highlights for the nuclear density gauge that generate a
This project focuses on evaluating new density property currently exist. Next, the
technologies that can characterize research team searched for new devices that
mechanistic properties in the field. could measure properties such as moisture
11 devices will be tested in the next phase of content, strength, stiffness, modulus, and
the project. uniformity. The research team examined the
features and capabilities of numerous systems
The basic premise for this project and then selected the most capable devices for
involves pursuit of a fundamental shift in the further evaluation.
methodology for acceptance of pavement After selecting devices that
layers. Traditionally, pavement layers are demonstrated potential application to
accepted based upon the contractor pavements, the research team procured these
satisfactorily compacting the layer to some devices through loan, lease, or purchase
specified dry density. However, pavement arrangements, and conducted testing with the
layers are designed based upon mechanistic devices. Strengths and weaknesses of all the
material properties such as strength and devices were noted, and the feasibility and
modulus. Additionally, TxDOT increasingly is applicability of each device were scrutinized
interested in measuring the uniformity of once more. Based upon the experiences with
quality over an entire project. The current each of the devices, the research team selected
random sampling quality-control/quality devices for use in the second year of this
assurance (QC/QA) system does not provide research project. The recommended devices
enough information to characterize the include:
uniformity of a project. Therefore, this project 1) AquaPro moisture probe - a dielectric-
focuses on evaluating new technologies that based, non-nuclear moisture
can characterize mechanistic properties in the measurement probe.
field, and developing and evaluating new 2) Vertek Soil MoisturelResistivity (SMR)
testing systems that can measure and quantify probe - a dielectric-based, non-nuclear
the uniformity of a project. moisture probe that can be driven into
As a starting point, the research team the soil with a dynamic cone
first searched for devices that could directly penetrometer (DCP) driver.
replace the nuclear density gauge. This search 3) Portable falling weight deflectometer
was initiated due to the strict regulations (PFWD) with three sensors - a hand-
involved in the use of the nuclear gauge. operated device that measures a
Unfortunately, no suitable direct replacements deflections bowl and provides data that
23
can be used to backca1culate the 10) Infrared imaging -- a technology that
modulus of individual pavement layers. provides the ability to measure the
4) Dynamic cone penetrometer -- a device uniformity of HMA paving operations.
with a conical tip that is driven into the 11) TxDOT falling weight deflectometer-
soil and traditionally used to measure TxDOT‘s standard field tool for
bearing capacity, but has been related to structural evaluation of pavements, this
modulus and Texas Triaxial device potentially could be used as a
Classification. final quality assurance check on a
5) Instrumented vibratory roller -- a completed pavement structure.
system utilizing an accelerometer on the Additionally, the level of coverage with
arm of a vibrating smooth-drum roller this device could provide enough
to measure displacement of the roller information to evaluate uniformity of
drum. Such a system can potentially the project.
measure the uniformity and stiffness
properties of a project. The research team recommends the
6) Automated proof roller -- a system primary focus of future work on this project
utilizing sensors to automatically consist of further development of systems that
measure the rut depth resulting from a provide virtually 100% coverage. These
proof rolling operation. Such a system systems include instrumented vibratory rollers,
potentially can measure uniformity and automated proof rollers, ground-penetrating
evaluate the stability/strength properties radar, and infrared imaging. The Texas
of a project. Transportation Institute (TTI) has operating
7) Ground-penetrating radar (GPR) -- a instrumented roller, GPR, and infrared imaging
system traditionally used for measuring systems, and the components to create an
layer thicknesses, GPR shows promise automated proof rolling system. The second
for evaluating the uniformity of a phase of this project should focus on evaluating
project and can potentially measure a system of controlling flexible pavement
moisture content of soils and bases. construction where a 100% coverage device is
Additionally, GPR can measure hot-mix first used on the section. After analysis in the
asphalt (HMA) density. field of the 100% coverage data, the research
8) Pavement Quality Indicator (PQI) -- a team will perform spot tests at specific
hand-held, dielectric-based spot- locations to evaluate what changes in material
measurement system for HMA properties exist. Finally, the team will make
pavement density. This device efforts to collect field samples for laboratory
particularly shows promise for use in testing. These samples will be used to evaluate
TxDOT density profile and joint density the relationship between field test data and
testing operations. laboratory properties. In this manner, the
9) Pavetracker Plus -- a new dielectric- research team will evaluate a model system that
based spot-measurement system for could control future construction projects.
HMA pavement density that potentially
has identical application as the PQI.
24
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Performance of Colorado’s First Rubblization Project on I-76 Near Sterling by Robert Laforce,
Yeh and Associates, 5700 E. Evans Ave., Denver, CO 80222 (Colorado Department of
Transportation – Research, 4201 E. Arkansas Ave., Denver, CO 80222) (Jan 2006)
Highlights When the decision was made to use the
The project used two methods of rubblizing rubblization techniques on this project, the
the concrete pavement, the resonant breaker original plans were revised to incorporate
and the multi-head hammer method. removing the existing 2-inch asphalt overlay,
Both rubblization methods appear to have rubblizing the concrete, and placing three two-
accomplished the required break-up of the inch lifts of HMA on the rubblized concrete.
old concrete pavement. The project used two methods of
Rubblization provides a cost-competitive rubblizing the concrete pavement, the resonant
tool in the rehabilitation of old concrete breaker and the multi-head hammer method.
pavements. Additionally, edge drains were installed to
control subgrade moisture. Crack and seat
This report documents the six-year technology was also to be constructed, but the
performance of the first rubblization of equipment was unable to adequately fracture
Portland cement concrete pavement (PCCP) the interlocked reactive aggregate slabs, so that
project built by the Colorado Department of treatment was not used.
Transportation (CDOT). The project was Since the technology was new to
selected to demonstrate the use of the resonant Colorado, a one-day seminar and open house
breaker and multi-head hammer methods of was held to describe the pavement design and
rubblization of a concrete pavement and the to demonstrate the rubblization processes. A
performance of the new hot mix asphalt (HMA) field trip to the construction site was included.
pavement overlay placed on the rubblized
concrete. Findings
The project is located on I-76 between o Falling weight deflectometer data from
Sterling and Iliff in Logan County. The existing 2004 shows that the pavement has
pavement was originally constructed in 1967 adequate structure to carry the traffic
and consisted of a two-inch emulsified asphalt loading on I-76.
treated base (Class 2) with eight inches of o The HMA pavement has no distresses
jointed plain concrete pavement (JPCP). Since associated with reflective cracking from
initial construction, this section of pavement the old concrete pavement and has not
has had limited maintenance. In 1995, this demonstrated any settlement, permanent
section was overlaid with a 2-inch asphalt deformation (rutting), or other distress
pavement, which was anticipated to be the as a result of the rubblization process.
bond breaker for the first phase of an unbonded o Both rubblization methods appear to
Portland cement concrete pavement (PCCP) have accomplished the required break-
overlay. up of the old concrete pavement. Both
25
methods should be allowed on future drains. Construction costs should
projects. include the installation of edge drains
o This project contained reactive and the cost of rubblization.
aggregate damaged concrete resulting in o Only small amounts of moisture were
tightly locked up slabs. No special noted in the edge drains, which may be
requirements for rubblization were a result of project soil type, or a result
needed to address this pavement of a 5-year drought in this area lasting
condition. The standard fracturing from 1999 to 2004. The moisture probes
required for each rubblization method worked from initial construction to late
was adequate to prevent damage to the 2001, and enough data was gathered to
new HMA overlay. document that the edge drains did
o The HMA pavement is performing prevent moisture from accumulating
similar to other newly constructed under the pavement
asphalt pavements and therefore any life
cycle calculations should be treated the Based on the performance of this
same as far as rehabilitation cycles or project, rubblization may provide CDOT with a
maintenance costs except for the cost-competitive tool in the rehabilitation of old
additional cost of maintaining edge concrete pavements.
26
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Are Highways Subsidized? in The Freeman by Randal O‘Toole (Foundation for Economic
Education, 30 South Broadway, Irvington-on-Hudson, New York, 10533; 1-800-960-4FEE;
http://www.fee.org/publications/the-freeman/article.asp?aid=6601) (Nov 2006)
Highlights streets and deed them over to the city or
Interstate Highways were funded entirely county, which then has to pay only for
with gas taxes and other highway-user fees. maintenance. Street maintenance, snow
For the last 60 years virtually no money removal, and other operations are as important
other than highway-user fees have been for pedestrians, cyclists, and public safety as
spent on any highways. for auto drivers.
User fees cover nearly 90% of the total Rail and transit advocates use the myth
amount spent on highways. of major highway subsidies to justify more
subsidies to Amtrak and public transit. Yet
Of the total amount spent on highways according to the Bureau of Transportation
in 2004, net subsidies amounted to $18 billion. Statistics, taxpayers pay at least 21 cents per
This is about 12% of total spending on road passenger-mile to subsidize Amtrak. Subsidies
construction, maintenance, and operations. to public transit in 2004 averaged 65 cents per
The myth of interstate highway passenger-mile, says the American Public
subsidies is most pernicious because it supports Transportation Association‘s Transit Fact Book
claims that postwar suburbanization is some 2005. (For the record, subsidies to air travel are
kind of plot rather than the preferred choice of about a tenth of a penny per passenger-mile.)
most American families. In reality, federal
highway planners originally expected to bypass The Social Costs of the Automobile
the cities and it was only lobbying by urban The Environmental Protection Agency
mayors that convinced Congress to run the and many American cities have spent millions
highways through cities. Those highways of dollars on numerous creative programs
reduced inner-city congestion and probably aimed at reducing driving. The only thing that
helped save many downtowns. has worked to clean the air, however, is to
The $18 billion subsidy it is trivial clean it at the tailpipe. Thanks to technological
compared with the nearly 4.7 trillion passenger- improvements, our air is far cleaner today than
miles carried on American highways in 2004. it was in 1970 when Congress first passed the
This is less than 0.4 cents per passenger-mile. Clean Air Act.
After adjusting for inflation, the total subsidy The average car on the road today
over the past 84 years has averaged less than produces about a tenth as much pollution as
0.5 cents per passenger-mile. cars in 1970. So even though we drive almost
A case could be made that some of three times as many miles as Americans did in
these local expenses are not even subsidies to 1970, all our cars together produce less than
driving. Streets existed and were paid for by 40% as much pollution. Many new cars today
local taxes long before automobiles. In most produce just one-hundredth as much pollution
modern subdivisions, developers build the
27
as 1970 cars, so the air will continue to get products. This product diversity is possible
cleaner even as driving increases. only because automobiles bring to the stores a
diversity of customers who may live many
The Benefits of the Automobile miles away.
The fortunes of the working class Thanks to autos, Americans enjoy far
turned around when Henry Ford developed the better housing than they had a century ago. In
moving assembly line in 1911, allowing him to the 15 years after 1945 U.S. homeownership
double wages while halving the price of his rates soared from 44 to 62% as millions fled
cars. Suddenly ordinary workers could afford to inner-city tenements for the suburbs.
buy the cars they made. Their increased This so-called ―sprawl‖ is the ―land-use
mobility allowed them to move to single-family impact‖ that auto critics want to count as a
homes that previously were occupied only by social cost of autos. But is it really so bad that
the wealthy and middle-class workers who more families get to live in suburban homes
could afford train or streetcar fares. with private yards? The 2000 census found that
Wide-scale auto ownership dramatically four out of five Americans live in ―urban
increased American mobility. History‘s most clusters‖ of 2,500 people or more, yet these
intensive network of intercity passenger trains urban clusters occupy just 2.6% of the land area
and urban transit was found in the United of the United States. Not only are we not
States in 1920. In that year the average running out of open space, thanks to
American rode about 1,200 miles per year on automobility most Americans enjoy their own
these passenger trains and urban transit lines. private open spaces in the gardens and play
Today, the average American travels about areas in their yards.
16,000 miles per year by automobile. Among the other benefits of auto
This 12-fold increase in mobility has technology are emergency medical care, rapid-
generated numerous benefits. It is no response fire and police services, and the
coincidence that, after adjusting for inflation, ability to evacuate in case of natural disaster.
worker incomes increased by more than seven Hurricane Katrina left thousands of families
times during the twentieth century. This is stranded because New Orleans has the lowest
partly because the automobile gave people auto ownership rate of any major American
access to more and better-paying jobs, but it is city. The news media reported lengthy traffic
also because the automobile transformed those jams when Hurricane Rita threatened the Gulf
jobs. Coast, yet every family with an automobile
As incomes increased, automobiles managed to escape the path of the storm long
simultaneously reduced consumer costs and before it hit.
greatly increased the variety of goods available Perhaps most important, autos are far
to consumers. Without cars, we would not have more egalitarian than the plush Pullman cars
supermarkets, club warehouses, home- and expensive streetcars of a century ago. More
improvement centers, or all sorts of other retail than 92% of American families own at least
categories and shops. In 1912 a typical one automobile, and whether you drive a 1985
American grocery store carried about 300 Yugo or the latest Cadillac, you have exactly
different products. Today, the average the same right to drive on any highway, road,
supermarket carries 20,000, many carry 50,000, or street in the nation.
and a few carry well over 100,000 different
28
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Parking Spaces/Community Places: Finding the Balance through Smart Growth Solutions
(Development, Community, and Environment Division, U.S. Environmental Protection Agency,
Washington, DC 20460) (Jan 2006)
Highlights supply a steady stream of office workers and
Zoning rules that require excessive parking residents who might patronize businesses in the
space hamper community development and area -- and less room to cluster other businesses
mobility. that will attract more foot traffic. Requiring
Parking requirements should be altered to more parking than the market actually demands
allow a better measure of the true demand adds substantial costs to development and
for parking and to balance parking with redevelopment, and in some cases the added
other community goals. costs will prevent development altogether. For
example, the future site of the D‘Orsay Hotel in
In calculating parking requirements, a prime location in Long Beach, California sat
planners typically use generic standards that for years as a low-revenue parking lot -- every
apply to individual land-use categories, such as developer who considered building on it was
residences, offices, and shopping. The most stopped in part by the high cost of building a
commonly used guidelines, issued by the garage to fulfill the city‘s minimum parking
Institute of Transportation Engineers in the requirement. It is under development today as a
Parking Generation Handbook, are based on hotel and retail complex in large part because
observations of peak demand for parking at innovative strategies reduced the parking
single-use developments in relatively low- burden on the developer.
density settings with little transit. In such Parking requirements are often copied
places, the destinations are widely separated, from one jurisdiction to another, and so are
parking is typically free, and walking, biking, remarkably consistent across different cities.
and transit are not available. As a result, Generic standards do not take into account the
planners assume in effect that every adult has a many highly local variables that influence
car, every employee drives to work, and every parking, such as density, demographics,
party visiting a restaurant arrives by car. Under availability of public transit, potential for
these conditions, parking can take up more than biking and walking, or the availability of other
50% of the land used in a development (see parking nearby. The obvious results of such
figure). For more compact, mixed-use, rigid requirements are big empty parking lots --
walkable places, these standards end up calling and they can also result in empty buildings.
for far more parking than is needed. Perfectly useable space in older buildings with
A surplus of parking really can be too limited or no on-site parking may prove
much of a good thing. It creates a ―dead zone‖ unrentable, because the businesses that would
of empty parking lots in the middle of what like to locate there are unable to meet high
ought to be a bustling commercial district or minimum parking requirements. The buildings
neighborhood. This dead zone means there is remain vacant, thwarting redevelopment plans.
less room for the offices and homes that would
29
Generic parking standards have simply development, including employees, customers,
not kept up the complexity of modern mixed- residents, and visitors. People of different
use development and redevelopment. But incomes and ages tend to have different car
parking requirements can be altered to allow ownership rates.
planners to better measure the true demand for Availability of transportation choices.
parking and to balance parking with wider Take into account the modes of transportation
community goals. This approach entails careful available to employees, visitors, and residents.
consideration of land-use and transportation Access to public transportation in a particular
characteristics that relate to parking demand. development, for example, can reduce parking
Successful examples consider the following demand. Walkable neighborhoods and bicycle
factors. amenities can also reduce parking demand.
Development type and size. Take into Surrounding land-use mix. Consider the
account the specific characteristics of the neighboring land uses and density to better
project: is there a large theatre that requires understand parking needs. For example, an
evening parking, or will small shops attract office building parking lot will be empty when
short-term, daytime patronage? Can the two the restaurant next door is packed, so requiring
share parking spaces? Parking demand is of both to provide for 100% of their parking needs
course also influenced by the size of the simply wastes space.
development, which is typically measured by Off-site parking. Consider the parking
total building square footage. that is already available nearby: on the street,
Development density and design. on nearby properties, or in public garages that
Consider the density of the development. may be available for users of a new
Research shows that each time residential development. On-street parking can be
density doubles, auto ownership falls by 32 to considered to reduce the amount of on-site
40%. Higher densities mean that destinations parking required for new development, or as a
are closer together, and more places can be reserve should new uses require more parking
reached on foot and by bicycle-reducing the than expected. On street parking has the added
need to own a car. Density is also closely benefit of acting as a buffer between
associated with other factors that influence car pedestrians and traffic, increasing the
ownership, such as the presence of good transit attractiveness of walking.
service, the community‘s ability to support Land use and demographic information
stores located in neighborhoods, and even the are important tools for establishing context-
walkability of neighborhood streets. specific parking requirements that better
Demographics. Consider the balance supply and demand for parking.
characteristics of the people using the
30
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Improving Pedestrian Safety at Unsignalized Crossings, NCHRP Report 562 by Kay Fitzpatrick,
et al. (Transportation Research Board, 500 Fifth Street, NW, Washington, DC 20001; (202) 334-
3213; http://gulliver.trb.org/bookstore) (2006)
Highlights to improve safety for pedestrians crossing high-
A proposed new pedestrian warrant is that volume, high-speed roadways at unsignalized
the number of pedestrians waiting to cross a intersections, in particular those served by
street should be no greater than the number public transportation; and (2) to recommend
of vehicles waiting to cross or enter a street. modifications to the Manual on Uniform
Median refuge islands or curb extensions as Traffic Control Devices for Streets and
alternatives to traffic control signals are Highways (MUTCD) pedestrian traffic signal
suggested. warrant.
The following walking speeds 3.5 ft/s for the The research team developed guidelines
general population and 3.0 ft/s for the older for use in selecting pedestrian crossing
or less able population are recommended. treatments for unsignalized intersections and
Red signal or beacon devices had midblock locations. Quantitative procedures in
compliance rates greater than 95%. the guidelines use key input variables (such as
In-street crossing signs had 87% pedestrian volume, street crossing width, and
compliance. traffic volume) to recommend one of four
possible crossing treatment categories: marked
There has been an increased emphasis crosswalk; enhanced, high-visibility, or ―active
on improving pedestrian safety. The desire to when present‖ traffic control device; red signal
improve pedestrian safety extends to areas or beacon device; and conventional traffic
typically seen as being non-pedestrian-friendly, control signal. The guidelines include
such as the higher speeds and wider roadways. supporting information for these treatment
With traffic conditions changing as traffic categories as well as examples and pictures of
volumes and congestion increase, pedestrians‘ traffic control devices in each treatment
ability to safely cross many roadways is category. The audience for these guidelines
affected. Recent developments in geometric includes state, county, and city traffic
design features, traffic control devices, and engineers; transit agencies; roadway designers;
technologies may improve pedestrian safety and urban planners; as well as consultants for
and access by addressing specific problems these groups and agencies.
associated with roadway crossings. Although The research team developed and
numerous treatments exist at unsignalized presented recommendations to the National
crossings, there is growing concern about their Committee on Uniform Traffic Control Devices
effectiveness. Thus, there is a need to identify to revise the MUTCD pedestrian warrant for
and study selected treatments to determine their traffic control signals. The proposed revisions
effectiveness. were derived from other vehicle-based traffic
This study had two main objectives: (1) signal warrants and supplemented with data
to recommend selected engineering treatments gathered during the study. The basis for the
31
proposed pedestrian warrant revisions is that resulted in the following walking speed
the number of pedestrians waiting to cross a recommendations: 3.5 ft/s (1.1 m/s) for the
street should be no greater than the number of general population and 3.0 ft/s (0.9 m/s) for the
vehicles waiting to cross or enter a street. Once older or less able population.
this basis was accepted, then the existing The research team chose motorist
vehicle-based warrants were used to derive compliance (that is, yielding or stopping where
comparable warrants for crossing pedestrians. required) as the primary measure of
In addition to traffic signal warrant revisions, effectiveness for engineering treatments at
the research team identified two other MUTCD unsignalized roadway crossings. In addition to
sections that could be revised. The first revision collecting motorist yielding behavior for
is a minor addition that suggests the use of general population pedestrians, the data
median refuge islands or curb extensions as collection personnel also staged street crossings
alternatives to traffic control signals. The to ensure consistency among all sites as well as
second revision is the inclusion of a new type adequate sample sizes. The study found that the
of highway traffic signal, Pedestrian Traffic crossing treatment affects motorist compliance.
Control Signals, in the MUTCD. Those treatments that show a red signal
In accomplishing the two main study indication to the motorist have a statistically
objectives, the research team also developed significant different compliance rate from
useful supporting information on various devices that do not show a red indication.
aspects of pedestrian safety at unsignalized These red signal or beacon devices had
roadway crossings. Two examples are the compliance rates greater than 95% and include
findings from the field studies on walking midblock signals, half signals, and high-
speed and motorist compliance. In total, 42 intensity activated crosswalk (HAWK) signal
study sites were selected in seven different beacons. Nearly all the red signal or beacon
states for the field studies. The study sites were treatments evaluated were used on busy, high-
chosen so as to distribute the different types of speed arterial streets. Pedestrian crossing flags
crossing treatments in certain regions, so that and in-street crossing signs also were effective
data for a particular treatment were not in prompting motorist yielding, achieving 65
collected from a single city. The field studies and 87% compliance, respectively. However,
included nine different types of pedestrian most of these crossing treatments were installed
crossing treatments. on lower-speed and lower-volume, two-lane
A total of 3,155 pedestrians were roadways. The measured motorist compliance
recorded during the field study. Of that value, for many crossing treatments varied
81% were observed as ―walking.‖ The considerably among sites. Number of lanes
remaining 19% of the pedestrians were being crossed and posted speed limit were other
observed to be running, both walking and factors in addition to type of treatment
running during the crossing, or using some influencing the effectiveness of the crossing
form of assistance (such as skates or bicycles). treatments.
Comparing the findings with previous work
32
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Underinflated Tires in the United States (United States Government Accountability Office, 441 G
Street NW, Room LM, Washington, D.C. 20548; http://www.gao.gov/new.items/d07246r.pdf)
(February 9, 2007)
Highlights NHTSA to develop regulations for installing a
Underinflated tires are unsafe and waste tire pressure monitoring system in new
fuel. passenger cars and light trucks. These
Tire pressure monitoring systems alert regulations are being phased in and will be
drivers when a tire‘s pressure falls below a effective for all new passenger cars and light
vehicle manufacturer‘s recommended level. trucks produced for the 2008 model year. The
Filing tires with nitrogen would reduce regulations will require a TPMS that will alert
leakage. drivers when one or more tires are
underinflated 25% below the vehicle
Underinflated tires impact a driver‘s manufacturer‘s recommended inflation pressure
ability to control a vehicle against skidding, or a minimum pressure specified in the
blowouts, and other tire failures. While not a regulation, whichever is higher. In addition,
leading cause of highway accidents and NHTSA works with industry to promote public
fatalities, a National Highway Traffic Safety awareness of the importance of properly
Administration (NHTSA) study shows that, in inflated tires, and the General Services
1999, underinflated tires contributed to 247 Administration (GSA) provides information on
(0.8%) of 32,061 fatalities and 23,100 (0.8%) the issue to federal agencies, such as the
of almost 3 million injuries. In addition, Department of Defense (DOD), that lease
NHTSA estimates that 41 vehicular-related vehicles.
deaths occur annually because of blowouts Several technologies are currently
alone from underinflated tires. Moreover, tires available to reduce tire underinflation, and all
that are not inflated to the appropriate pressure of them have the potential to increase safety
result in a slight decline in fuel economy. The and fuel economy when used appropriately.
Department of Energy‘s designated economist The federal government and industry
on this issue indicated that, of the 130 billion recommend using a tire pressure gauge to
gallons of fuel that the Transportation Research check pressure regularly and reinflate tires to
Board (TRB) estimated were used in passenger maintain proper inflation. Also, tire pressure
cars and light trucks in 2005, about 1.2 billion monitoring system (TPMS) equipment for
gallons were wasted as a result of driving on passenger cars and light trucks will alert drivers
underinflated tires. when a tire‘s pressure falls 25% below a
The federal government is using vehicle manufacturer‘s recommended level or
legislation, public information, and educational minimum activation pressure specified in the
programs to inform the public about tire regulations, whichever is higher.
underinflation. For example, the Transportation When there is a need to increase tire
Recall Enhancement Accountability pressure, consumers generally have a choice
Documentation (TREAD) Act of 2000 required between two products—compressed air and
33
nitrogen. Compressed air is readily available at when the results of this work will be made
service stations and retail tire outlets public. NHTSA expects to complete testing on
nationwide and is either free or relatively nitrogen inflation‘s effects on the rate of loss of
inexpensive for consumers. However, inflation pressure and nitrogen inflation‘s
compressed air leaks from tires over time. effects on tire aging by April 2007 and March
Nitrogen permeates through tires slower than 2007, respectively. Currently, relatively few
air and studies have shown that tires filled with nitrogen outlets are available for consumers to
nitrogen retain pressure levels longer and age use, and while the cost of nitrogen varies, it can
more slowly. However, researchers pointed out exceed the cost of compressed air. The
that nitrogen has not been assessed under materials used to make tire innerliners, can
normal driving conditions. Transport Canada, affect the amount of air and water vapor
the Canadian government‘s transportation permeability. Finally, single-wide tires and the
ministry, has been studying the benefits of use of pressure management and tire pressure
nitrogen inflation in truck tires and expects to monitoring systems on large trucks can also
complete this work in early 2007. It is unclear reduce the incidence of underinflated tires.
34
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Bridge Rating Practices and Policies for Overweight Vehicles, NCHRP Synthesis 359 by
Gongkang Fu and Clementine Fu, Troy, Michigan (Transportation Research Board, 500 Fifth
Street, NW, Washington, DC 20001; (202) 334-3213; http://gulliver.trb.org/bookstore) (2006)
Highlights These weight policies have evolved
Overweight vehicle permitting is operated over the years to make accommodations for
through a highly complex system. local industry needs and the needs of
The multi-state permit programs of the New specialized vehicles and industries. The
England Transportation Consortium and policies may be difficult to modify for the
SASHTO represent a successful model for following reasons:
improved uniformity in oversize/overweight o The permit trucking industry has made
permitting. an economic investment based on these
policies. Changing the policies would
Most states developed tools or change the interstate and intrastate
methodologies years ago that determined the competitive playing field.
allowable weight limitations and vehicle o The personnel who developed these
dimensions for permit vehicles in their polices are no longer employed at the
jurisdictions. Some of the approaches that agencies. The present personnel are
states have used are: reluctant to make significant changes
o Determine allowable permit axle and/or without additional studies or electronic
axle group weights by increasing computer modeling of the bridges that
Federal Formula B weights by some would support the considered changes.
amount. Resources are frequently not available
o Develop a permit design and analysis for the studies or computer models.
vehicle and set the allowable axle group
weights based on the load effects of this Some states now have various
vehicle. electronic computer models, which allow them
o Use locally developed methodologies to more flexibility to make changes. This also
extrapolate allowable permit weights contributes to the non-uniformity in permit
from the bridge design loading. weight policies and practices. Apart from the
o Use weight limitations that are policy differences, the specifications for bridge
legislated rather than derived based on evaluation also allow ample room for variation
engineering concepts. because they do not have specific enough
o Use basic weigh policies of adjacent provisions.
state(s) with modifications.
Conclusions
Note that these approaches not only In the United States, overweight vehicle
establish the maximum axle and/or axle group permitting is operated through a highly
weights, but may also affect the axle spacing or complex system that involves many agencies at
number of axles required to carry the weight. the state and local levels. The governing
35
policies and regulations vary extensively and involved quantities has allowed for the various
significantly in terms of permit type and observed interpretations.
processing operation. The industry has a strong Having electronic models of the bridges
interest in enhanced uniformity in this area. that can repeatedly be used for bridge
Bridge evaluation for permit review as a evaluation is an effective approach to enhanced
step in the permitting system also varies uniformity for permit review. It can reduce
noticeably among the state-level agencies, turnaround time for permit review, allow for
primarily as a result of variation in more effort on examining other options for
interpretation of the AASHTO Manual for approving the permit, and provide more
Condition Evaluation of Bridges (2000) and the consistent and accurate results.
referenced AASHTO Standard Specifications The multi-state permit programs of the
for Highway Bridges (2002), and possibly also New England Transportation Consortium and
as a result of the differences in the computer SASHTO represent a successful model for
software programs used. The Southeastern improved uniformity in oversize/overweight
Association of State Highway and permitting. In these programs, one permit can
Transportation Officials (SASHTO) study be applied in all participating states for
shows that the difference in the allowable interstate trips if the vehicle falls within the
vehicle weight for one single case can be as defined specifications for dimensions, gross
high as 40%. Note that the lack of specific vehicle weight (GVW), axle weights, and/or
provisions in these specifications for the other parameters.
36
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Design and Construction Guidelines for Geosynthetic-Reinforced Soil Bridge Abutments with a
Flexible Facing, NCHRP Report 556 by Jonathan T. H. Wu, Kevin Z. Z. Lee, Sam B. Helwany,
Kanop Ketchart, University of Colorado at Denver (Transportation Research Board, 500 Fifth
Street, NW, Washington, DC 20001; (202) 334-3213; http://gulliver.trb.org/bookstore) (2006)
Highlights for three types of flexible facing-geotextile-
A design method and construction wrapped, timber, and natural rock-are
guidelines for geosynthetic reinforced soil presented.
(GRS) abutments with a flexible facing have The major refinements and revisions to
been developed. the NHI design method are as follows:
The allowable bearing pressure of a
A design method and construction bridge sill on the load-bearing wall (the lower
guidelines for geosynthetic reinforced soil wall) of a GRS abutment is determined as a
(GRS) abutments with a flexible facing have function of the friction angle of the fill,
been developed in the course of this study. The reinforcement vertical spacing, sill width, and
design method adopted the format and sill type (isolated sill or integrated sill). A
methodology of the National Highway Institute simple three-step procedure is provided for
(NHI) manual for the design of mechanically determination of the allowable bearing
stabilized earth (MSE) bridge abutments. pressures under various design conditions.
Fourteen specific refinements and revisions of The default value for reinforcement
the NHI design method are presented, and the vertical spacing is set at 0.2 m. To ensure
basis for each refinement and revision is satisfactory performance and an adequate
provided. The refinements and revisions are margin of stability, reinforcement spacing
based on findings from previous case histories, greater than 0.4 m is not recommended for
full-scale loading experiments, and finite GRS abutments under any conditions.
element analysis of GRS abutments, as well as To provide improved appearance and
the authors‘ experiences and knowledge on greater flexibility in construction, a front batter
GRS structures in general and GRS abutments of 1/35 to 1/40 from the vertical is
in particular. recommended for a segmental abutment wall
The construction guidelines were facing. A typical setback of 5 to 6 mm between
established based on the guidelines for successive courses of facing blocks is
segmental GRS walls as provided by various recommended for 200 mm (8 in.) height blocks.
agencies as well as the authors‘ observations The reinforcement length may be
and experiences with the construction of GRS ―truncated‖ in the bottom portion of the wall
walls and abutments. The construction provided that the foundation is ―competent.‖
guidelines focus on GRS abutments with a The recommended configuration of the
segmental concrete block facing. As the truncation is: reinforcement length = 0.35 H at
literature on construction of GRS abutments the foundation level (H = total height of the
with other forms of flexible facing is rather abutment wall) and increases upward at a 45
limited, only the basic construction guidelines deg angle. The allowable bearing pressure of
37
the sill, as determined in the three-step settlement. A typical RSF is formed by
procedure, should be reduced by 10 percent for excavating a pit 0.5 * L deep (L =
truncated-base walls. Permitting truncated reinforcement length in the load-bearing wall)
reinforcement typically will translate into and replacing it with compacted road base
significant savings when excavation is involved material reinforced by the same reinforcement
in the construction of the load-bearing wall of a to be used in the load-bearing wall at 0.3-m
bridge abutment. vertical spacing.
A recommended ―sill clear distance‖ Both a minimum ultimate tensile
between the back face of the facing and the strength and a minimum tensile stiffness of the
front edge of the sill is 0.3 m (12 in.). The reinforcement should be specified to ensure
recommended clear distance is a result of finite sufficient tensile resistance at the service loads,
element analysis with the consideration that the to provide adequate ductility, and to ensure a
soil immediately behind the facing is usually of sufficient safety margin against rupture failure.
a lower compacted density because a heavy A recommended procedure for determining the
compactor is not permitted close to the wall required minimum tensile stiffness (at 1.0
face. percent strain) and the minimum ultimate
For most bridge abutments, a relatively tensile strength are stipulated.
high-intensity load is applied close to the wall It is recommended to extend the
face. To ensure that the foundation soil beneath reinforcement lengths in both the upper and
the abutment will have a sufficient safety lower walls, at least the top three layers of each
margin against bearing failure, a revision is wall, to about 1.5 m beyond the end of the
made to check the contact pressure over a more approach slab to promote integration of the
critical region - within the ―influence length‖ abutment walls with the approach embankment
Dl (as defined in Chapter 3) behind the wall and the load-bearing abutment, so as to
face or the reinforcement length in the lower eliminate the bridge ―bumps‖-a chronic
wall, whichever is smaller. In the current NHI problem in many bridges.
manual, the contact pressure is the average Connection strength is not a design
pressure over the entire reinforced zone (with concern as long as the reinforcement spacing is
eccentricity correction). kept not more than 0.2 m, the selected fill is
If the bearing capacity of the foundation compacted to meet the specification stipulated
soil supporting the bridge abutment is found in the recommended construction guidelines,
only marginally acceptable or somewhat and the applied pressure does not exceed the
unacceptable, it is recommended that a recommended design pressures in the
reinforced soil foundation (RSF) be used to recommended design method.
increase bearing capacity and reduce potential
38
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Development of LRFD Specifications for Horizontally Curved Steel Girder Bridges, NCHRP
Report 563 by John Kulicki, Wagdy Wassef, Danielle Kleinhans, Chaih Yoo, Andrzej Nowak,
Mike Grubb (Transportation Research Board, 500 Fifth Street, NW, Washington, DC 20001; (202)
334-3213; http://gulliver.trb.org/bookstore) (2006)
Highlights design provisions was required to ensure
The two design examples are available on smooth merging of these provisions into the
the AASHTO website. then-existing straight girder design provisions.
The original organization of the
AASHTO‘s Guide Specifications for NCHRP 12-52 project called for a two-phase
Horizontally Curved Highway Bridges approach. Phase I was intended to produce
(hereafter referred to as the ―Guide curved bridge design provisions that were
Specifications‖) was first published in 1980. based on the information available at that time.
The specifications were based on work These specifications were intended to be
conducted in the late 1960s and early 1970s by revised in Phase II based on the results of the
a group of researchers called the ―Consortium then-ongoing research on curved bridges. This
of University Research Teams‖ (CURT). The research was funded by the Federal Highway
research work resulted in guidance on the Administration (FHWA). Several universities
analysis of curved bridges and equations for collaborated with the FHWA in conducting this
determining the strength and checking the research.
stability of curved girders. An updated version Phase I of the NCHRP 12-52 project
of the Guide Specifications was published in produced curved bridge design provisions as
1993. The 1980 Guide Specifications was planned. It also produced two design examples,
written in the allowable stress design (ASD) one of a box-girder bridge and the other of an I-
format. The 1993 Guide Specifications was girder bridge. However, at that time it became
written in both the ASD and the load factor clear that the FHWA-sponsored research would
design (LFD) format. As a result of the work produce a new set of design provisions that
on the National Cooperative Highway Research would be applicable to both straight and curved
Program (NCHRP) 12-38 project, the Guide bridges and that would have some terms of the
Specifications were updated again and the equations ―dropping out‖ when applied to
updated version, written in the LFD format, straight bridges. The new set of provisions was
was published in 2003. considered to be a significant improvement
In 1999, the NCHRP 12-52 project was toward streamlining the design provisions. It
initiated to develop design provisions for was decided not to publish the design
curved bridges in the AASHTO load and specifications developed in Phase I of the
resistance factor design (LRFD) format. These project and to develop a new set of
provisions were intended to be incorporated specifications and design examples based on
into the specifications to extend the the results of the FHWA-sponsored research in
specifications‘ coverage to curved bridges. Phase II. These provisions were approved by
Statistically calibrating the curved bridge ballot of the AASHTO Highway Subcommittee
39
on Bridges and Structures (HSCOBS) in 2003 comparison indicated that member
and 2004 for straight girders and curved proportions will not be significantly
girders, respectively. The straight girder altered in unanticipated ways and that
provisions were published in the third edition anticipated changes manifested
of AASHTO LRFD specifications in 2004. The themselves in the example bridges.
curved girder provisions were published in the o The updating of the I-girder and box-
2006 interim to the AASHTO LRFD girder bridge design examples. These
specifications. examples, originally produced in the
In addition to the recommended NCHRP 12-38 project, were updated in
specifications that were subsequently adopted Phase I of the project and then updated
by AASHTO, the NCHRP 12-52 project again in Phase II based on the new
resulted in the following: design provisions developed in Phase II
o The statistical calibration of the load of the project.
and resistance factors for curved
bridges. This calibration indicated that The curved bridge design provisions,
the factors developed for straight the statistical calibration work, and the
girders are applicable to curved girders. comparison between the existing designs and
o The comparison of resistance analysis those conducted using the new provisions are
conducted using the AASHTO Guide included in this report. The two design
Specifications for curved bridges to examples are available on the AASHTO
those conducted using the new LRFD- website at
based design provisions. Twenty-one http://www.transportation.org/sites/bridges/doc
existing bridges provided by several s/Box%20Girder.pdf and
state DOTs and 11 simulated bridges http://www.transportation.org/sites/bridges/doc
were used in this comparison. The s/I-Girder.pdf.
40
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Transit Agency Participation in Medicaid Transportation Programs, TCRP Synthesis 65 by
Kenneth L Hosen and Elisabeth Fetting, KFH Group, Inc., Bethesda, Maryland (Transportation
Research Board, 500 Fifth Street, NW, Washington, DC 20001; (202) 334-3213;
http://gulliver.trb.org/bookstore) (2006)
Highlights coordinate services with NEMT programs. The
In rural areas, NEMT funding is often report identifies and examines barriers and
greater than public transit funds. actions (at all levels) that can foster or inhibit
This review is conducted to assist transit coordination at the local level. The overall
agencies in exploring opportunities to focus of this effort is on how transit agencies
coordinate services with NEMT programs. coordinate services with NEMT.
A literature review was undertaken to
Non-Emergency Medical examine coordination efforts between medical
Transportation (NEMT) has existed since the transportation and public transportation; NEMT
mid-1970s. From the beginning of the program, service models (which have a significant effect
coordination was employed to maximize scarce on the potential for coordination);
resources in rural areas. During this period, administrative/management/monitoring issues;
many rural agencies and some urban agencies and other pertinent concerns, such as cost
successfully coordinated NEMT service with allocation. Most of the coordination literature
public transit and/or other human service focused on state level efforts, although a
programs. However, opportunities still exist for handful of documents addressed local level
public transit agencies in both urban and rural coordination with transit agencies. The
areas to participate in the NEMT program as literature included articles on fixed-route bus
providers of service or as brokers. Although service; cost transferring onto Americans with
rural transit agencies have historically taken Disabilities Act paratransit; working
advantage of coordination opportunities, there relationships between NEMT and public transit
are a growing number of urban transit agencies and among state and local Medicaid officials,
that are seeing opportunities for coordination state departments of transportation (DOTs), and
with benefits for customers, transit agencies, transit system officials; and uniform service
and state Medicaid agencies. standards.
Medicaid is a large funding resource for Next, surveys were conducted to
transportation across the country. In rural areas, understand the real and perceived barriers to
NEMT funding is often greater than public the coordination of NEMT and public
transit funds and virtually dwarfs other human transportation, Thirty surveys were distributed
service transportation programs in terms of to three types of stakeholders; 10 each to transit
funding and priorities. Any coordination effort agencies, state DOTs (transit divisions), and
that does not include Medicaid risks omitting corresponding state Medicaid agencies. A total
the largest participant. of 22 stakeholders responded, including 8 state
This review is conducted to assist Medicaid agencies, 6 state DOTs, and 8 transit
transit agencies in exploring opportunities to agencies.
41
The survey results indicated a variety of Other issues raised included the need
barriers and challenges at all levels of for additional expertise, suggesting that there is
government. A number of issues emerged, a need for additional training and
some new and some recurring. It is apparent communication for all parties; service standards
from the surveys that certain service delivery and the lack of common safety and operational
models encourage coordination, whereas other standards; and coordination.
models do not. Operational issues included the Five case studies were undertaken that
complicated and time-consuming process of reflected geographical diversity; urban, small
trip intake for NEMT, with some agencies urban, and rural agencies; and different service
indicating that this was such a difficult process delivery models. Problem areas as well as
that their participation was inhibited. successes were examined. For each case study,
Jurisdictional barriers of crossing service area a transit system and its relationship with the
boundaries and the cost of taking vehicles long state Medicaid agency, as well as the
distances were discussed as well. relationship between the state Medicaid agency
and the state DOT were reviewed.
42
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Evaluation of the Clearview Font for Negative Contrast Traffic Signs by Andrew J. Holick, Susan
T. Chrysler, Eun Sug Park, and Paul J. Carlson, Texas Transportation Institute, Texas A&M
University System, College Station, Texas 77843-3135 (Texas Department of Transportation,
Research and Technology Implementation Office P.O. Box 5080, Austin, Texas 78763-5080;
979.845.1734; http://tti.tamu.edu) (Apr 2006)
Highlights be no difference between any of the treatments.
Clearview font is inferior to the current Additional statistical testing confirms that all
FHWA font. the fonts performed the same (i.e., were
recognized at the same distance) during the
The initial evaluation in this project was daytime conditions. The results during the
a laptop study. The results from this effort nighttime conditions showed that replacement
indicate that using a mixed case font such as of the FHWA font with Clearview produced the
Clearview does not significantly increase the worst overall nighttime recognition distance,
readability of a negative contrast sign when both quantitatively and statistically.
compared to the same sign in an all uppercase Legibility Distance: Like the
font. Subjects showed similar correct response recognition analysis, the legibility analysis
rates for each sign. The particular message shows that all the main effect variables except
appeared to have more effect on readability gender are statistically significant. Daytime
than font. If drivers are actively searching and legibility distance is greater than nighttime for
anticipating possible messages on signs given all font treatments. Further analysis by either
their trip destination and roadway context, a day or night shows that none of the font
mixed case footprint may allow them to more treatments was significantly different from the
quickly identify their desired sign and extract other. The interaction effect between the lines
the necessary information. of legend and font treatment shows that two-
Recognition Distance: The recognition line legend signs have a slightly higher
task was performed in order to determine if legibility distance than three-line legend signs.
drivers benefit from the use of an However, for both lengths of legend there is no
upper/lowercase font over that of an all- significant difference between the font
uppercase font when identifying a word (or treatments. When it comes to sign color, the
destination name in the case of guide signing) results were mixed. For fluorescent yellow
based on the word‘s footprint. Main effect signs, all the fonts performed statistically the
variables such as age group, visual acuity, day same. For white signs, the standard FHWA
versus night, treatments, and target line were all performed better than any of the alternates. For
identified as being statistically significant, as fluorescent orange signs, Treatment C
one might expect. The statistically significant outperformed all other treatments. No single
interactions are of particular interest here, font treatment consistently outperforms the
however. For instance, in Figure 24 the others as a function of sign color. The straight
interaction of day-night and treatment is shown. replacement of the FHWA font with the
During the daytime conditions there appears to recommended Clearview font generally
43
provides one of the least legible scores within with the use of the Clearview font on
each sign color. negative contrast traffic signs.
o The daytime recognition analysis from
Conclusions the field study showed the three
o The positive contrast version of alternative fonts provided statistically
Clearview underwent several similar recognition distances as the
modifications before it was approved current FHWA font senes.
for use by the FHWA. o The nighttime recognition analysis from
o The benefits of the positive contrast the field study showed that
version of Clearview were thoroughly recommended straight replacement of
documented through a series of research Clearview provided shorter recognition
projects spanning approximately a distances than the current FHWA font
decade. Until this research project was series. However, the results also showed
completed, the performance of the that the next thicker stroke width
negative version of Clearview had not version of the Clearview negative
been rigorously tested, through contrast font produced statistically
simulation or road testing. similar recognition distances as the
o An analysis of the SHSD book shows current FHWA font series.
that there is little consistency with o Both the daytime and nighttime
respect to the design of negative legibility analysis from the field study
contrast signs. showed that the three alternative fonts
o The laptop survey revealed no specific provided statistically similar legibility
or consistent indications concerning the distances as the current FHWA font
possible performance gains associated series.
44
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Motorist Comprehension of Traffic Control Devices for Mobile Operations by Melisa D. Finley,
Brooke R. Ullman, and Nada D. Trout in Transportation Research Record 1948 (Transportation
Research Board, 500 Fifth Street, NW, Washington, DC 20001; (202) 334-3213;
http://gulliver.trb.org/bookstore) (2006)
Highlights approaching. Thus, researchers do recommend
Drivers frequently misunderstand mobile the use of the ―# Vehicle Convoy‖ sign instead
sign information. of the ―Work Convoy‖ sign on the back of the
A number of recommendations aimed at trail vehicle for mobile operations. A mobile
improving driver comprehension are made. operation typically consists of two to four
vehicles, so the number needs to be adjustable
Maintenance work is often and easily changed.
accomplished through the use of mobile work
zones. Mobile operations typically consist of TABLE 7: Information on Passing and
one or more vehicles that move along the road Comprehension Percentages
Percent
intermittently or continuously at quite slow
Treatment Correct Incorrect
speeds relative to the normal traffic stream.
Current devices 66a 34
Such operations present challenges in regard to b
installing traffic control devices-that is, the Pass on Shoulder text message 97 3
Pass on Right text message 83c 17
devices must progress along with the work
Use Shoulder text message 81c 19
area. ‗Based on a confidence interval test (alpha = 0.5), this percent is statistically
In Texas, the ―Work Convoy‖ sign is less than 85%.
bStatistically different from the current setup, Pass on Right text message, and
currently used on the back of a trail vehicle Use Shoulder text message at a 95% level of confidence.
‗Based on a confidence interval test (alpha = 0.05), this percent is not
(i.e., the last work vehicle in a mobile statistically different than 85%.
operation, the first vehicle that motorists
encounter) to inform motorists that they are Even though the ―Your Speed‖ display
approaching multiple work vehicles. However, (showing speed of approaching vehicles) used
the motorist survey showed that only 53% of in the San Angelo District was understood by
participants interpret the ―Work Convoy‖ sign 93% of survey participants, this display does
to mean that there is more than one work not provide information to motorists about the
vehicle in the road ahead. The ―Moving speed of the work vehicle and thus the large
Vehicles‖ and ―Moving Operation‖ signs also speed differential between that of the work
resulted in low comprehension levels (52% and convoy and approaching traffic. Nevertheless,
37%, respectively). the ―Your Speed‖ display may yield effects
Placing the number of work vehicles on (e.g., alert motorists, decrease approach speeds)
the sign (i.e., ―3 Vehicle Convoy‖) improved that increase the safety of mobile operations-
comprehension (79%, not statistically different although that was not evaluated in this research
from the 85% criterion), for the participants project. Thus, future research should evaluate
were provided with more specific information the operational effects of the ―Your Speed‖
about the number of work vehicles they were display.
45
The displays of ―My Speed‖ and ―Your For the ―Slow Work Convoy‖ and
Speed‖/‖My Speed‖ resulted in low ―Slow 3 Vehicle Convoy‖ signs, use of the
comprehension levels (53% and 62%, word ―slow‖ was interpreted to mean that the
respectively). The ―My Speed‖ display was participant should slow down. In contrast,
interpreted by approximately one-third of the participants thought that the ―Slow Moving
participants as the speed at which they were Vehicles‖ and ―Slow Moving Operation‖ signs
traveling, instead of the speed of the work meant that the work vehicles were going
vehicle. Some confusion may be attributed to slowly. However, addition of the word ―slow‖
the text ―My Speed.‖ There was also evidence did not significantly change the participants‘
that the ―Your Speed‖/‖My Speed‖ display perception of the work vehicle speed. Thus,
contained too much information for participants researchers do not recommend the use of the
to correctly interpret. From the motorist survey word ―slow‖ to describe the speed of mobile
results, researchers do not recommend the use operations.
of the displays ―My Speed‖ and ―Your In Texas, when mobile operations are
Speed‖/‖My Speed.‖ However, future research being conducted on the centerline of a two-
should evaluate the potential of the ―Me‖ speed lane, two-way roadway with improved
display. shoulders, motorists are directed by a right
Not surprisingly, including the word flashing arrow panel to pass the work convoy
―moving‖ on static signs (―Moving Vehicles‖ to the right on the improved shoulder. Only
and ―Moving Operation‖) improved motorists‘ 66% of participants understood that they were
understanding that the convoy is mobile. That supposed to pass the work vehicles to the right,
word also seems to imply lower work vehicle under the current setup. All of the alternative
speeds. However, the ―Moving Vehicles‖ and messages (―Pass on Shoulder,‖ ―Pass on
―Moving Operation‖ signs were not understood Right,‖ and ―Use Shoulder‖) improved the
by participants to mean that they were comprehension rate. However, the ―Pass on
approaching more than one work vehicle. Thus, Shoulder‖ message was understood by the
researchers do not recommend the use of the highest percentage of participants, at 97%.
―Moving Vehicles‖ and ―Moving Operation‖ Thus, researchers recommended that the ―Pass
signs. To convey to motorists that they are on Shoulder‖ message be evaluated in the field
approaching multiple work vehicles and that to determine if it improved compliance. An
the work vehicles are moving at low speeds, earlier research report documents the results of
future research should evaluate the potential of a small field study conducted to determine if
the word ―moving‖ in combination with the the ―Pass on Shoulder‖ message improved
number of vehicles, for example, ―3 Moving motorists‘ compliance of passing the work
Vehicles.‖ convoy to the right on the improved shoulder.
46
TRANSPORTATION RESEARCH DIGEST
ARIZONA TRANSPORTATION INSTITUTE
e-mail jsemmens@cox.net
APRIL 2007
Traffic Congestion in North Carolina: Status, Prospects and Solutions by David T. Hartgen,
Professor of Transportation Studies, University of North Carolina at Charlotte,
dthartge@email.uncc.edu (John Locke Foundation, 200 W. Morgan, Suite 200, Raleigh NC 27601;
Info@johnlocke.org; http://www.johnlocke.org/site-docs/traffic/TrafficCongestion.pdf) (Mar 2007)
Highlights ineffective projects that will not likely affect
State and local planners are not targeting congestion.‖
enough transportation dollars toward Hartgen graded each of the state‘s 17
reducing traffic congestion. metropolitan regions on its congestion
Without additions to road capacity, the reduction plans. Charlotte earned the worst
projected population growth in each region grade, D, while only three regions – Asheville,
will add significantly to traffic congestion. Goldsboro, and Jacksonville – earned A-
Instead of saying that transit programs grades. ―For most parts of the state, the bottom
should get 20-50% of funds, modes of line is clear: other actions will be needed to
transportation should get funds in proportion reduce or maintain current congestion levels.‖
to their demand. The new study builds on a 2006 report
Hartgen prepared for the Los Angeles-based
Future road congestion will threaten Reason Foundation. The Reason report showed
North Carolina‘s economy unless the state traffic delays would increase by 65% across the
refocuses its transportation priorities. That‘s the United States by 2030. North Carolina needs to
key message in a new Policy Report from the spend $12.4 billion to clear congested urban
John Locke Foundation and Reason roads and prepare for traffic growth in the next
Foundation. 25 years, according to that report.
―Congestion in North Carolina will For his new report, Hartgen reviewed
more than double over the next 25 years,‖ said more than 1,300 specific transportation projects
study author David Hartgen, Professor of planned for each North Carolina region‘s
Transportation Studies at the University of transportation plan. Hartgen evaluated each
North Carolina at Charlotte. ―Charlotte drivers project based on its likely impact on congestion
will face the same type of traffic delays relief, then compared that impact to the
Chicago drivers face now. Raleigh‘s delay will congestion growth forecast for the region.
nearly double, to present-day Minneapolis Some regions are devoting too little
levels. Even smaller cities like Rocky Mount money to the congestion problem, Hartgen
will see a significant increase in traffic delays.‖ said. The state‘s largest regions are spending
State and local planners are not significant chunks of transportation funding on
targeting enough transportation dollars toward transit instead.
reducing those delays, said Hartgen. ―That ―In the Charlotte region, 43% of
increased congestion threatens the state‘s available dollars are proposed for highway
economic future,‖ he said. ―Yet many regions projects, and the road improvements proposed
have ignored the problem and propose would alleviate only one-third of the predicted
spending limited transportation funds on increase in congestion,‖ he said. ―Raleigh and
47
Durham are allocating 73% and 49%, intersection designs; increasing the weight
respectively, of their dollars to effective placed on congestion in selecting projects;
projects.‖ implementing flex-time, ridesharing, and work-
Programs in other communities were at-home programs; removing bottlenecks;
judged more effective. Those plans often had improving intersection turns and signal
enough savings to relieve congestion, if systems; expanding incident management
targeted at the right projects. programs; using tolls and public-private
North Carolina does not need new partnerships; and planning land use and
funding to address the congestion problem, transportation capacity jointly.
Hartgen said. ―The report recommends using The state cannot afford to ignore
existing planned funds for congestion relief,‖ growing congestion problems, Hartgen said.
he said. ―In some cities, ‗balance‘ in ―North Carolina is not generally recognized as
transportation funding needs to be redefined. one of the most congested states, but it is,‖ he
Instead of saying that transit programs should said. ―My recent national assessment ranked
get 20-50% of funds, modes of transportation North Carolina 48th among the 50 states in
should get funds in proportion to their urban interstate congestion.‖
demand.‖ ―Pulled by competing priorities, many
Hartgen‘s report offers nearly 20 communities appear to be focusing largely on
recommendations for the state and numerous other objectives and are de-emphasizing the
individual recommendations for each region. congestion problem,‖ Hartgen added.
The statewide proposals include: changing the ―Refocusing efforts on relieving congestion
highway distribution formulas to account for could have a major economic impact by saving
congestion; appointing ―congestion tsars‖ and travel time. The report estimates the value of
establishing congestion reduction programs for travel time saved at about $855 million
each region; using innovative highway and annually.‖
48
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