Studies in the last decade have investigated the effect of built

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Praveen K Maghelal PhD (Corresponding Author)
Assistant Professor
Department of Public Administration
University of North Texas
1155 Union Circle #310617
Chilton Hall, Rm 204K
Denton, TX 76203-5017 USA
Ph: (940) 565 3786
Praveen.Maghelal@unt.edu


Cara Jean Capp
Clean Water Action / Clean Water Fund
190 NE 199th Street, Suite 106
Miami, Florida 33179
305.653.9101 office
239.994.9393 cell
ccapp@cleanwater.org




                                        1
                        Walkability: A Review of Existing Pedestrian Indices.



Abstract:

Several indices have been developed in the last two decades that quantify and evaluate the

walkability and bikability of communities. This study reviewed the twenty-six pedestrian indices

for its scale of measurement type of data source(s) of the data and the list of specific variables

used to develop the index. The identified variables were classified into 11 constructs such as

sidewalk road intersection vehicle pleasantness safety etc. Doing so helped identify the specific

constructs of built-environment that were used to develop these indices. Furthermore a normative

framework to objectively measure the built-environment constructs that influence walking using

GIS was developed.



Keywords: Objective measures, walkability, built environment




                                                  2
INTRODUCTION



Studies in the last decade have investigated the effect of built-environment on walking in the

community (Ball et al. 2001, Booth et al. 2000, CDC 2001, Troped et al. 2001, Handy et al.

2002, and Greenwald and Boarnet 2002). Along with other socio-psychological factors various

environmental correlates have been identified that influence walking in general (Sallis et al.

1999, Sallis et al. 1997, Giles-Corti and Donovan 2002a, CDC 2001, Brownson et al. 2001,

Giles-Corti and Donovan 2002b, Saelens et al. 2003a, and Pikora et al. 2003). Although these

studies indicate that walking trips are influenced by the characteristics of the neighborhood

comprehensive built-environment constructs still remains to be investigated. It is important to

identify this comprehensive list of variables because using them can significantly add to the

regression models of walking beyond socio-demographic variables (Eg. Kockelman 1997, Frank

and Pivo 1994, Kitamura Mokhtarian and Laidet 1997). It is also important because only few

variables of built-environment have been empirically analyzed for its impact on walking in

communities and the need for comprehensive and detailed environmental measures is essential

(Clifton et al 2007, Kwon et al 1998, Painter 1996).

       Recent attempts to review the existing literature for these comprehensive and detailed

environmental measures (Moudon and Lee 2003 and Clifton et al. 2007) investigated the existing

audits instruments level of service indicators Indices checklist etc. associated with both walking

and biking. The study by Moudon & Lee (2003) investigated the measures associated with

walking and biking. Although a large number of these measures show similar relationship with

both walking and biking there are not exactly the same. It is therefore important to look at these

measures separately for walking and biking. Therefore the study by Clifton et al (2007) reviewed



                                                 3
the recent pedestrian audits only. This study extends the knowledge of identifying the constructs

associated with walking by reviewing the existing pedestrian indices. Such a review has never

been performed and it is imperative to do so for two reasons. First while audits measure the

quantity of built-environment associated with walking indices and level of services rank the

location segment or an area as „less or most suitable to walk‟. These indices and level of service

use a single aggregate value determined from the measures of built-environment available

through audits GIS and other objective and subjective measures. Therefore an index extends the

quantification done using audits and assigns a suitability value for walking in the community.

Second as mentioned earlier although several built-environment constructs report similar relation

walking and biking they are not the same. Therefore it is important to identify what specific

constructs of built-environment were used specifically to measure the suitability to walk in the

pedestrian indices alone. This can help identify the constructs that have been either spuriously

included or excluded in earlier studies and thus can be used in future studies. Similar study with

all the biking related indices can be performed to identify the comprehensive and detailed

measure of biking in communities.

       Therefore this study reviewed twenty- five pedestrian indices (Bradshaw 1993, Bandara et

al. 1994, Khisty 1994, Dixon 1996, City of Portland 1998, Portland Pedestrian Master Plan 1998,

Milazzo 1999, Allan 2001, USDOT, Landis et al. 2001, Moudon 2001, Gallin 2001, City of Ft.

Collins 2002, Moudon et al. 2002, Wellar, Saelens et al. 2003, Dannenberg 2004, Frank et al.

2004, Rodriguez et al. 2005, McCormack et al. 2006, Kim et al. 2006, Hoehner et al. 2006, and

Shah 2008) that were developed during the last two decade to develop a comprehensive and

detailed measures of built-environment variables related to walking. Beyond the creation of this

inventory this study has three primary goals: (1) It categorizes these measures based on its



                                                 4
method of measurement as subjective objective and distinctive (2) It categorizes the objective

variables based on its geographical and spatial structure and (3) It introduces standardized

measures that can be used to evaluate these variables in GIS.

       The following section discusses the existing literature reviews and presents the case to

identify and measure the constructs of built-environment associated with walking. The next

section discussed the methodology used to identify the indices. It discusses the criteria based on

which these indices were selected for the review and categories based on which the variables are

classified. The result section discusses the outcome of the review and classifies the variables

reviewed into objective subjective and distinctive variables. The final section discusses the

conceptual framework to objectively measure the built-environment variables and classifies the

variables based on this framework.

Audits and Instruments



The assessment of the physical walking environment has been done using methods such as audits

tools scales instruments checklists inventories level of service survey questionnaires and indices.

These assessment methods can be classified into two major groups based on the outcome.

Assessment using methods such as scales level of service and indices are used to quantify the

amount of built-environment features into a single number that categorizes the physical

environment as high versus low or moderately suitable to walk. Conversely methods such as

audits surveys and checklist tend to measure the amount of built-environment features that either

support or hinder walking in communities.

        Two studies in the recent past have reviewed the existing assessments of built-

environment (Moudon and Lee 2003, Clifton et al. 2007). The study by Moudon and Lee (2003)



                                                 5
proposed a Behavioral Model of Environments (BME) that identified the constructs of physical

environment supportive of walking and biking into three components: 1) The Origin and

Destination of the walk or bike trip (or locational characteristics) 2) The Characteristics of the

Route Taken for these trips (or segmental characteristics) and 3) The characteristics of the Area

(or areal characteristics) in which the trip takes place (Figure 1).




             Figure 1. The BM E model o f Built-environ ment proposed by Moudon and Lee (2003)




The BME suggests that „all three components of the behavioral model of environments must be

considered to measure comprehensively the effect of the environment on walking and bicycling

for transportation.‟ This study based on the interaction of behavior and environment classified

the variables as spatiophysical spatiobehavioral spatiopsychosocial and policy. Although their

study states that the components of BME can be captured as points lines and polygons they did

not classify those variables based on their spatial characteristics. This can help to standardize the

method of measuring each variable for future studies.


                                                    6
       Also as reported by Clifton et al. (2007) „In sum the important factors contributing to

“walkability” are still very much in contention …. Among the complications is the nature of the

measures: some aspects of the pedestrian environment can be measured objectively and therefore

with more ease but others are more subjective in nature. ’ However their review of pedestrian

audits focused only on the pedestrian environment compared the use of Pedestrian

Environmental Data Scan (PEDS) audit based on the characteristics (field protocol PDA/tablet

PC compatibility etc) and the items measured (land uses walking etc) with other audits such as

WSAF SPACES etc. Their study did not classify these variables based on the method of

measurement such as subjective or objective. So why is this classification of variables based on

the method of measurement as subjective or objective important?

Measuring Built-environme nt Variables



The study by Moudon and Lee (2003) reported that „the lack of detailed and accurate data on

both behavioral and objective measures of environments likely represents the single most

important issue to address in future attempts to isolate individual or groups of environmental

predictors of walking and bicycling.‟ Also Forsyth et al. (2006) reported that „measures

developed in urban geography planning and transportation may not be relevant to research on

physical activity and public health researchers are not always aware of the problems with

physical environment data.‟ So less standard approaches exist to measure the objectively

measurable data in GIS.

       Until the last decade or so most studies that have objectively measured the built-

environment did not use GIS. Most of these studies either used self- measured environmental

correlates or conducted audits to objectively measure store and analyze the effect of built-



                                                7
environment on walking. Aggregated level of information was used by stud ies that used GIS for

objective measure of built-environment. One of the primary reasons for this was unavailability of

physical environment data at disaggregated level. With recent improvements in technology to

create and store data at disaggregate level, studies have used GIS for objective measure of built-

environment (Aultman-Hall et al. 1997, Moudon et al. 1997, Rodriguez and Joonwon 2004,

Frank et al. 2005, Lee and Moudon 2006a). GIS has been an effective tool for evaluating

walking accessibilities in neighborhood designs (Aultman-Hall et al. 1997) and lately has been

used to evaluate the built-environment in recent studies (Pikora et al. 2002, Troped et al. 2001).

Bauman et al. (2002) encourage the use of GIS system because GIS-derived measures can help

overcome some of the methodological problems of reliance on self- reported environmental

factors.

           Conversely studies have reported that self- reported measures have shown to have lesser

reliability compared to objective measures derived using GIS. A recent study by Frank et al.

(2005) rightly reported that to date almost all studies that have analyzed built-environment have

used perceived measure of built-environment. Objective measure on the other hand can be more

reliable and thus needs to investigate in its use for assessment of built-environment. They

developed a walkability index that used objective measures in GIS of land- use mix residential

density and street connectivity.

           Therefore this study develops a comprehensive list of built-environment variables related

to walking and classifies them based on the method of measurement as objective subjective and

distinctive (see Table 1). It further classifies the objective variables based on their spatial and

geographical (BME) characteristics. Finally it proposed some standard measures of these

objective variables in GIS.



                                                   8
  Variable                                                                    Methods of     Unit of

    Type                                 Definition                          Measurement     Analysis      Examples

                   Variables that can be quantified using a standard                        Location,     Intersection,

                   method of measurement that can be replicated in                          segment,      street, land-

Objective          other studies                                             GIS or Audit   or area       use

                   Variables that can be quantified using a standard                        Individuals   Perception,

                   method of measurement that can / cannot be                Audit or       or any of     Local

Subjective         replicated in other studies                               Survey         the above     architecture

                   Variables that can be quantified using a method of                                     Cautious

                   measurement that may or may not be replicated in                                       driving,

                   other studies. More often used in a particular analysis   Audit or       Any of the    Line of

Distinctive        only.                                                     Observation    above         sight



 Table 1. Type of built-environment variables.



 METHOD

 Source of Literature



             The literature search to identify the pedestrian indices replicated the methodology used

 by Lee and Moudon (2003) to review the walking and biking instruments. Literature in urban

 planning health and transportation were reviewed for pedestrian indices in the academic and

 web-based databases such as TRIS MEDLINE and Web of Science using pedestrian indices

 audit measurement built-environment and physical activity as keywords. Only literature that




                                                             9
measured or quantified correlates of physical built-environment (as index) were included for the

detailed review.

Review and Classification of Constructs/Indicators



       Variables extracted from the reviewed literature were grouped based on the physical

constructs of built-environment associated with walking. The variables were classified into four

dimensions and ten constructs. The design dimension included the distance the sidewalk the road

the intersection the vehicle and the lateral separation. The density dimension included the

demographic variables while the diversity dimension included the land use variables. The quality

dimension included the safety and comfort/convenience variables. Doing so helped to identify

the specific constructs of built-environment that were used to develop the pedestrian indexes

over the span of two decade. Also these indices were reviewed for the scale of measurement type

of data source(s) of the data and the list of specific variables used to develop the index.

       The variables classified under each physical construct were categorized based on the

method of measurement as objective subjective and distinctive. While distinctive variable are

more often unique to each study objective and subjective variables are the most commonly used

in most studies till date. While subjective or self- reported variables use individual‟s perception

and behavior as method of measurement they have shown to have low reliability as reported by

Bauman et al. (2002). Objective variables on the contrary are used because the method of

measurement can be replicated to capture the same variables.

       Following that the objective variables alone were classified based on the geographical

characteristics (the BME Model) as locational segmental and areal, and the spatial characteristics




                                                 10
                                                     Physical Environmental Factors


                                                                              Subjective                                               Walking in
                                                           Objective
                                                           Measures           Measures                                                 Neighborhood


                                                                Individual Factors

                                                     Relationship Conceptualized             Relationship under investigation

           Schema of type of physical environmental factors that may influence walking in
           neighborhood
      Adapted and Modified fro m Pikora Corti et al. 2003. Social Science & Medicine (56).
    BME Categorization of Built-Environment




                                                   Physical Environmental Factors
                                                                                             Spatial Categorization of BE Variables




                                               Locational                 Point Features
                                              Characteristics


                                               Segmental                   Line Features                                               Walking in
                                              Characteristics                                                                         Neighborhood
‘

                                                  Areal                      Polygon
                                              Characteristics                Features


                                                       Individual/Personal Factors




Figure 2. Conceptual framework of walking using GIS measures




                                                                                        11
                                                                                                                       Data

Author                  Index                                                        Unit of Analysis   Data Source    Measured

Allan                   Walking Permeab ility Indices                                Area               GIS            Objective

Bandara                 Grade-Seperated Pedestrian Systems                           Area               Unclear        Objective (?)

Bradshaw                Walkability Index                                            Area               Survey         Both

Dixon                   Pedestrian Performance Measures                              Segment            Audit          Objective

DOT                     Walkability Checklist                                        Area               Survey         Subjective

FDOT                    Florida Pedestrian Level o f Service                         Segment            Audit          Objective

Fort Co llins           Pedestrian Level-of-service                                  Area               Audit          Both

Khisty                  Qualitative level of service                                 Segment            Survey         Subjective

Moudon                  Pedestrian Infrastructure Prio rit ization Decision System   Area               GIS            Objective

Moudon                  Pedestrian Location Identifier 1                             Area               GIS            Objective

Moudon                  Pedestrian Location Identifier 2                             Area               GIS            Objective

Portland                Pedestrian Deficiency Index                                  Segment            GIS            Objective

Portland                Pedestrian Environmental Factor                              Area               Unclear        Objective

Portland                Pedestrian Potential Index                                   Segment            GIS & Survey   Objective

Gallin WA-LOS           Pedestrian Level of Service                                  Segment            Audit          Both

Wellar                  Basic walking security Index                                 Intersection       Audit          Both

Dannenberg (Virginia)   Walkability Audit Tool                                       Segment or A rea   Audit          Both

Highway Manual          Level of Service                                             Segment            Audit          Objective



                                                                    12
Saelens et al (2003)     Neighborhood Environ ment Walkab ility Scale   Area      Survey        Both

Frank et al              Walkability Index                              Area      GIS           Objective

Rodriguez et al (2005)   Built Environment Index for Walking            Area      GIS           Objective

McCormack et al (2006)   Walkability Index                              Segment   Audit & GIS   Objective

Kim et al (2006)         Level of Service (LOS) Indicator               Segment   Survey        Subjective

Hoehner et al (2006)     Active Neighborhood Checklist                  Segment   Audit         Both

Krambeck Shah (2008)     Pedestrian infrastructure                      Area      Survey        Both

Table 2. Review of existing pedestrian indices.




                                                                 13
such as point line and polygon (Figure 2). Standard measures of these objective variables are

then proposed for use in future studies.

RESULT



This study reviews 25 „pedestrian indices‟ that evaluate walking in communities. The primary

need for this review was to identify built-environment variables associated with walking (only)

that can be objectively measured using GIS. Therefore indices developed in the last two decades

to quantify the pedestrian environment were selected from the existing literature. The indices

were reviewed for the scale of measurement type of data source(s) of the data and the list of

specific variables used to develop the index (Table 2) and physical constructs of built-

environment.

Unit of Analysis



       The scale of measurement of each index is identified by the quantification of pedestrian

variables for an area segment or location. For example the index developed by Wellar quantified

the suitability to walk based on the intersection features and thus the scale of measurement was

the location (of intersection). Whereas the Khisty‟s Qualitative Level of Service quantified the

pedestrian suitability for a road segment and thus the scale of measurement is the road segment.

From the reviewed indices 13 indices quantified the suitability for an area ten quantified a

segment and one measured the suitability to walk at a location (intersection). The walkability

audit tool developed by Dannenburg can evaluate the suitability to walk at the scale of both

segment and area.




                                                14
Sources



       It was important to identify the sources of the data used to evaluate the suitability to walk

because it helped in classifying the variables into objective or subjective variables. It has to be

noted that either due to unavailability of diligent methods or technology some variables used in

certain indices were measured subjectively either through survey or site audit. With the current

improvements both due to availability of data and the technology these variables can be

measured objectively in GIS. Only seven indices used GIS measures to develop their index.

Fourteen indices used either survey or site audits to develop the index. It was unclear from the

literature if the Grade-Separated Pedestrian Systems by Bandara and the Pedestrian

Environmental Principal component for Portland used a survey GIS or aerial imagery to evaluate

each variable used to develop the respective index. The Portland Potential Index used both GIS

and measures obtained through survey to quantify the suitability to walk while the walkability

index (McCormack) used both audit and GIS for its evaluation.

Type of Data



       The pedestrian indices were reviewed to list the specific variables used to quantify a

score of suitability to walk. Once these variables were identified they were evaluated if the

variables used for that index could be measured objectively using GIS. For example Khisty‟s

Level of Service was assessed using perception of the environment and therefore was subjective

to the location and the observer whereas the Dixon‟s Pedestrian Performance Measure uses

variables that can be measured using GIS and were thus classified as objective variables. In the

currently reviewed indices for this study 13 indices used variables that can be objectively



                                                 15
measures using GIS three were purely based on perception and were thus subjective and eight

indices used both objective and subjective variables to quantify the suitability to walk. Since the

index by Bandara was not clear of its data source the type of data used is unclear as well.

Measure of Indices



The variables of each index were categorized into ten different constructs of built-environment

(Table 3) and the frequency of these constructs used across all the indices was evaluated. The

physical construct of land use was the most commonly used construct (16 of 25 indices) across

various indices followed by the construct of sidewalk (in 15 indices) road (in 14 indices) and

intersection (in 12 indices). Lateral separation distance and safety were the constructs least used

(in six indices) across the 25 indices.

Classification of Constructs and Indicators



       In total 85 variables were identified from the 25 indices reviewed (Table 4). Of the 85

variables 53 were identified as objective variables that can be measures in GIS 21 were identified

as subjective variables and 11 as distinctive variables. It has to be noted here that certain

variables such as sense of security can be audited or surveyed and incorporated in GIS whereas

other variables such as the pedestrian friendly commercial area although not available all the

regions across the nation can be calculated in GIS. However for this study variables that can be

readily identified using aerial image survey audit and are not available to self-reported or

subjective to individuals were not categorized under the objective section of the variable. Also

built-environment variables such as crosswalk signalization curb-cuts already encompasses the




                                                  16
                                                   Design                                     Density      Di versity            Quality

                                                                               Lateral                                              Comfort /

Author               Distance   Sidewalk   Roads     Intersection   Vehicles   Separation   Demographics   Land-Use     Safety      Convenience

Allan-WPI                X          -          -            -           -           -            -             -            -              -

Bandara-GSPS             X          -         X             -           -           -            -             X            -              X

Bradshaw-WI              -         X           -            -           X           -            X             X            X              X

Dixon-PPM                -         X          X             X           X           X            -             X            -              -

DOT                      -         X          X             X           X           X            -             -            -              X

FDOT-LOS                 -         X          X             -           X           X            -             -            -              -

Fort Collins-LOS         X         X          X             X           -           -            -             -            X              X

Khisty-QLOS              X         X          X             X           X           -            -             X            -              X

Moudon -PIPDS            -          -          -            -           -           -            X             X            -              -

Moudon-PLI1              -          -          -            -           -           -            X             X            -              -

Moudon-PLI2              -          -          -            -           -           -            X             X            -              -

Portland-PDI             -         X          X             -           X           -            -             -            -              -

Portland-PEF             -         X          X             X           -           -            -             -            -              -

Portland-PPI             X          -          -            -           -           -            -             X            -              -

Gallin WA-LOS            -         X          X             X           X           X            -             X            X              X

Wellar-BWSI              -          -          -            X           -           -            -             -            -              -

Dannenberg-WAT           -         X           -            X           X           X            -             -            -              X

Highway Manual-LOS       -          -          -            X           -           -            X             -            -              -

Saelens et al-NEWS       -          -         X             -           -           -            X             X            X              X

Frank et al- WI          X          -         X             -           -           -            -             X            -              -




                                                                         17
 Rodriguez et al (BEI-W)   -      X         X          -   -     -   X   X    -   -

 McCormack et al (WI)      -      X         X          X   X     -   -   X    X   X

 Kim et al (LOS-I)         -      X         -          -   -     -   X   X    -   -

 Hoehner et al (ANC)       -      X         X          X   X     X   -   X    -   X

 Shah (PI)                 -      X         -          X   -     -   -   X    X   X

 Total occurrence          6      15        14        12   10    6   8   16   6   11



Table 3. Factors used to develop the pedestrian indices.




                                                            18
                         OBJ ECTIVE                   SUBJ ECTIVE             DISTINCTIVE


         Distance:       (1) Origin to destination

                         (2) Actual Dis/ Min Dis

                         (3) Distance to Schools

                                                                              (1) Alternate Walking

         Sidewalk:       (4) Availability             (1) Visib ility         Facility

                         (5) Connectivity             (2) Maintenance

                         (6) Width

                         (7)

                         Continuity/Coverage/Densi

                         ty

                         (8) Location

                         (9) Slope

                                                                              (2) Imp rovement of
Design




         Roads:          (10) Connectivity            (a) Driveway            Roadway

                         (11) Width                   (3) Frequency/Volu me

                         (12) Median

                         (13) No. of Lanes

                         (14) Netwo rk

                         (15) Road Density

         Intersection:   (16) Density                 (4) Co mfort            (3) Right turn conflict

                         (17) Safety                  (a) Crosswalk

                         (18) Size                    (5) Visib ility

                         (a) crosswalk                (b) Signalization

                         (19) Availability            (6) Visib ility

                         (20) Cu rb-cuts              (7) Synchronization

                         (b) signalization


                                                     19
                            (21) Availability

            Vehicles:       (22) Speed                     (8) Not Cautious

                            (23) Vo lu me

                            (24) Parking

            Ped Support                                                       (4) Sociability of

            Facilities:     (25) Shoulder Lane                                Co mmunity

                            (26) Sidewalk Bu ffer                             (5) Po licy Variables

                            (27) Parkways

                            (28) Green-ways/Trails


            Demographics:   (29) Population Density

                            (30) Housing Density

                            (31) Employ ment Density

                            (32) Ethnic Minority

                            Density
Density




                            (33) Transit Co mmuters

                            (34) Bike Co mmuters

                            (35) Pedestrian

                            Co mmuters/Usage

                            (36) Households with cars




            Land Use:                                                         (6) Pedestrian

                                                                              Classification, reg ion 2040

                            (37) Land Use Mix                                 classification
Diversity




                                                                              (7) Pedestrian Friendly

                            (38) Parcel Size                                  Co mmercial Area

                            (39) Multimodel Facilit ies                       (8) Travel Demand Support

                            (40) Co mpactness                                 (9) Type of future project



                                                          20
                         (41) Recreational

                         (42) Essential

                         (43) Administrative

                         (44) Other Develop ment




          Safety:        (45) Traffic Security        (9) Sense of Security      (10) Clear Sight Lines


                         (46) Personal Security

          Comfort/

          Convenience:   (47) Lighting                (10) Attractiveness        (11) Exp loration/ View

                         (48) Street Tree             (11) Visibility

                         (49) Benches/HH              (12) Local Arch itecture

                         (50) Bu ilding Frontage      (13) Attractive Delight
Quality




                         (51) Topography              (14) Interest

                         (52) Shade and Rain Cover    (15) Maintenance

                         (53) Weather/Climate         (16) Odor

                                                      (17) Ventilation

                                                      (18) No ise

                                                      (19) Crowd ing

                                                      (20) Dogs

                                                      (21) Absence of

                                                      concealed area



Table 4. Classification of variables as objective subjective and distinctive.




                                                     21
             Objecti ve Vari ables      Measure that can be used in GIS                       Index of Measure

                                                                                              Moudon-PIP, Gallin-WA LOS,

Locational   Crosswalk - Availability   No. of crosswalks / Intersection                      Dannenburg-WAT, CWS-PQS

                                                                                              Dixon-PPM, Portland-PEF,

             Crosswalk - Size           Length of crosswalk (street width)                    Dannenburg-WAT,

                                                                                              Bradshaw-WI, Moudon-PIP,

             Curb-cuts                  Nu mber of cu rbcuts per intersection                 Dannenburg-WAT,

             Intersection Safety        Nu mber of accidents at the intersection              Moudon-PIP(location)

             Location of sidewalk       Distance of sidewalk fro m edge of road               McCormack - PI

             Building Frontage          Distance of build ing fro m end of sidewalk (width)   Hoehner-ANC

                                                                                              Fort Co llins-LOS, Moudon-PIP,

             Availability of Signals    No. of signals / Intersection                         Portland-PEF, HCM-LOS

                                                                                              Moudon-PIP, Gallin-WA LOS,

Segmental    Intersection Density       No. of Intersections / total length of road           HCM-LOS

                                                                                              Dixon-PPM, Fort Collis-LOS,

             Lighting                   Nu mber of street lights                              Moudon-PIP

             Street Tree                Nu mber of streets trees                              Dixon-PPM, FDOT-LOS

Areal        Traffic Security           Nu mber of vehicu lar and pedestrian accidents        Portland-PDI, SSBC-NEWS

             Personal Security          Nu mber of burg lary assaults and theft               Khisty-QLOS (Perception), Gallin -


                                                                            22
                                                                                               WALOS, CWS-PQS, SSBC-NEWS

            Recreational            No. of parks and theaters/cinema/ fitness center parcels   Moudon-PLI, SSBC-NEWS

            Essential               No. of stores and shopping center parcels                  Moudon-PLI, SSBC-NEWS

            Admin istrative         No. of school post office and bank parcels                 Moudon-PLI, SSBC-NEWS

                                    No. of facilities that serve more than one mode of

            Multimodal Facilities   transportation

            Safety                  Nu mber of accidents in the area                           Moudon-PIP(location)

            Benches/HH              Nu mber of benches per household                           Bradshaw-WI



Table 5a. Built-environment variables measured as point features




                                                                       23
                  Objecti ve

                  Vari ables                        Measure that can be used in GIS                                      Index of Measure

             Sidewalk

Locational   Availability            Availability of sidewalk                                             FDOT-LOS, Dannenburg-WAT,

             Sidewalk

             Connectivity            No. of Intersections with 4 curb-cuts / total no. of intersections   Portland-PEF, Dixon-PPM, Moudon-PIP

                                                                                                          Dixon-PPM, Bradshaw-WI, Fort Collins-LOS,

             Sidewalk Width          Average width of the sidewalk                                        FDOT-LOS, Gallin-WALOS, Dannenburg-WAT,

             Road Width              Average total width of the road                                      Dixon-PPM, Portland-PDI, Moudon-PIP

             No. of Lanes            total number of through lanes                                        Fort Co llins-LOS

                                                                                                          Dixon-PPM, Portland-PDI, Moudon-PIP, FDOT-

             Speed                   Avg. speed on roads                                                  LOS, Dannenburg-WAT,

                                     Total width of road - (No. of through lanes * Avg. width of

             Shoulder Lane           lanes)                                                               FDOT-LOS

                                                                                                          Dixon-PPM, FDOT-LOS, Gallin-WALOS,

             Sidewalk Buffer         Width of shoulder lane + Width of landscaped strip                   Dannenburg-WAT,

Segmental    Origin to destination   Length of distance of origin to destination                          Bandara-GSPCS,

             Actual Dis/ Min Dis     Ratio of network distance by straight line d istance                 Allan-WPI, Fort Collins-LOS

             Distance to Schools     Length of travel d istance to schools                                Portland-PPI

             Sidewalk Continuity     Total length of sidewalk on one or both sides / total length of      Bradshaw-WI, Fort Collins-LOS, Port land-PDI,


                                                                               24
                                  road network                                                     Moudon-PIP, Port land-PEF

            Sidewalk Slope        gradient rise of the sidewalk along a certain length             McCormack-PI, Hoehner-ANC

                                                                                                   Khisty-QLOS, Portland-PPI, Gallin-WALOS,

            Road Connectivity     No. of Intersections / total length of road                      SSBC-NEWS, Fran k et al-WI

            Median Length         Length of 2-way roads with median/total length of 2-way roads    Dixon-PPM

                                                                                                   Portland-PEF, Portland-PDI, Moudon-PIP, FDOT-

            Vo lu me of Traffic   Avg. volume of vehicles on roads (ADT)                           LOS, Gallin-WALOS, Dannenburg-WAT,

                                  Gridiron = 1 Frag mented Parallel = 0.75 warped parallel = 0.5

                                  loops & lollipops = 0.25 and lollipops on a stick = 0 (for 4

 Areal      Road Network          quadrants)                                                       Portland-PEF, Bandara-GSPCS, Port land-PPI

            Road Density          Total length of road network in an area                          Rodriguez-BEIW

            Green-ways            Avg. length of off-road path                                     Dixon-PPM

            Trails                Avg. length of pedestrian trail                                  Dixon-PPM

            Parkways              Avg. length of park trails                                       Dixon-PPM



Table 5b. Built-environment variables measured as line features.




                                                                            25
                  Objecti ve Vari ables                    Measure that can be used in GIS               Index of Measure

Locational   Parking                      On-street and Off-street parking per household            Bradshaw-WI, FDOT-LOS

             Weather/Climate              Avg. temperature at COOP stations closest to study area   Khisty-QLOS

                                                     n                                          Moudon-PLI2, Moudon-
                                                     ( pi ) ln( pi )  / ln( n)
                                                     1                                          PLI1, Bandara-GSPCS,

                                          p-proportion of sq. ft of landuse i n-no. of landuses     Moudon-PIP, Port land-PPI,

                                                                                                    SSBC-NEWS, Fran k et al-

             Land Use Mix                                                                           WI

                                                                                                    Portland-PEF, Moudon-PIP,

Segmental    Topography                   Change in elevation in the unit area                      Portland-PPI2,

                                                                                                    Dixon-PPM, Dannenburg-

             Shade and Rain Cover         Amount of sidewalk covered by tree canopy                 WAT,

             Population / Population                                                                Moudon-PLI1, Bradshaw-

Areal        Density                      Total population per unit area                            WI, Moudon-PIP,

                                                                                                    Moudon-PLI2, Moudon-

                                                                                                    PLI1, Portland-PPI, SSBC-

             Housing Density              Total housing (types) per unit area                       NEWS, Fran k et al-WI

             Emp loy ment Density         Total employ ment per unit area                           Moudon-PIP, Port land-PPI2,

             Ethnic M inority Density     Total minority population per unit area                   Moudon-PIP


                                                                               26
            Households with cars          Avg. number of cars per household                                   Moudon-PIP

            Transit Co mmuters            Total number of public transit users per unit area                  Rodriguez-BEIW

            Bike Co mmuters               Total number of co mmuters on bike per unit area                    Rodriguez-BEIW

                                                                                                              Rodriguez-BEIW, Kim-

            Pedestrian Co mmuters/Usage   Total number of pedestrians per unit area                           LOS(I)

            Parcel Size                   Avg. size of parcel in a unit area                                  Portland-PPI2,

                                                                                                              Moudon-PLI2, Moudon-

            Co mpactness                  No. of non-residential parcel per residential parcel in unit area   PLI1, Moudon-PIP

            Other Deve lopment            No. of new permits issued per unit area                             Moudon-PLI1, Moudon-PIP,

Table 5c. Built-environment variables in the Areal category.




                                                                         27
variable “traffic calming” measure. Henceforth to avoid duplication these variables were

acknowledged but not included in further analysis of this study.

       The outcome of this classification indicates that various indices have used varying

measure of same built-environment variables to quantify walking. For example the Portland PEF

measures topography using a point system whereas Moudon-PIP measures it using ease of

walking. Similarly the speed limit measured by Dixon-LOS uses a threshold of 56 mph for a

point system whereas the Portland-PDI uses five threshold points. On the other hand though not

empirically tested the volume of traffic is measured similarly (as ADT) by all the indices. This

calls for standardization of measuring built-environment variables so that the result of the same

can be compared across locations efficiently. GIS can provide a standardized method that can be

replicated across studies and that can use the information available from various audits to

quantify the walking environment.

       Measurement of objective variables can be standardized when they can be conceptualized

clearly based on their spatial characteristic in GIS. However development of a standardized

measure has the limitation associated with other GIS studies which is with the available of

spatial data at fine-grain resolution the method of measurement of objective variables can vary.

Nonetheless with commonly available data the table 5(a, b, c) classifies the objective variables

obtained from the review of 25 pedestrian indices based on the conceptual framework of

variables measured using GIS (refer Figure 2). Fifty-three objective variables were classified into

point line and polygon features that represent the locational segmental and areal categories.

       Tables (5a-c) groups and lists the measures based on its geographical and spatial

characteristics. Objective measures of these variables in GIS are proposed which can be used by

future studies. Also existing indices that used these variables have been indicated from the



                                                28
literature. It has to be noted that the list of variables influencing walkability is comprehensive

only till the time of this study. As new studies develop new indices more variables can be added

to this comprehensive list of variables.

DISCUSSION AND CONCLUSION

        Two important outcomes of this study are: (1) categorization of built-environment

variables measured in GIS based on its unit of analysis, and (2) identification of built-

environment constructs and its measure that were most commonly used to quantify walking. This

study is important because although a large number of environmental audits have been

developed with increased use of technology such as PDA remote sensing and GIS data

(Scholessberg et al. 2008, Rodriguez 2006, Forsyth 2006) and have been used to investigate the

role of built-environment variables on walking biking or physical activity they have not been

used aggregately to measure the walkability in communities. It is important to do so because it is

the aggregate affect of all significant predictors of walkability that affect the amount of

pedestrian activities.

        This study attempts to investigate the use of GIS to objectively measure the built-

environment. Twenty-five pedestrian indices were reviewed to develop a list of variables that are

associated with walking. These variables were classified into objective subjective and distinctive

variables based on the possibility to measure these variables in GIS. Also the indices were

reviewed for the sources and types of data to investigate the extent of use of GIS and objective

measures in developing these indices. Although the review indicated that only a few indices used

GIS to measure the variable that form a composite index it is indicative of availability of better

data and technology to evaluate these variables objectively in GIS. Therefore to further the scope

of this analysis a conceptual framework that can objectively measure the built-environment



                                                 29
variables in GIS were classifies based on their spatial and geographical characteristics.

Appropriate and easily adaptable measures of these variables were identified and listed that can

be adapted by future studies. This standardization of measure can help compare the outcome of

each study better than otherwise.

       This analysis is not without limitations. Most of the indices used to develop the variables

are not validated for its measure of each variable or for its aggregated quantification of built-

environment. Similar concern was raised by Lee and Moudon (2003) in their analysis as well.

However this study does not discuss the validity of these indices but reviews these indices to

identify the variables and constructs that constitute the index. Also development of future indices

will be influenced by this investigation. Future indices can attempt to use the built-environment

variables obtained from this review and use the current studies that identify the variables that

report significant influence on walking. Also other variables not used so far such as the natural

amenities scale developed by US department of agriculture combines six standardized measures

of climate typography and water bodies that reflect natural qualities most people prefer can be

included in the analysis.

       Future indices also need to be validated for its adaptability and capability to address the

specific characteristics of the study area using methods of fuzzy logic and multi-criterion

evaluation. Therefore periodical revisit of literature will be required to identify and develop

measures of built-environment related to walking and for biking.

       This study has important implications for planners and health professionals alike. Firstly

the use of constructs sparsely across the indices indicate that a more comprehensive index is

required that encompasses all the constructs of built-environment. Secondly increasing use of

technology indicates that micro- level analysis of built-environment is feasible with the only



                                                 30
restriction of availability of data at that level. Therefore planners and health professionals while

focusing on the larger context of built-environment should also collect use and evaluate micro-

level data that can be objectively measured (indications of which are the use of PDAs for

environmental assessment). Finally with the evolution of new variables and constructs

appropriate method that can be used and replicated by other studies should be developed. This

will help studies to either use a standardized method of measuring the objective variables or

build on the existing measures using improved technology method or data. This study provides a

starting point in developing standard measures of objective built-environment variables that can

be replicated by other studies in future.



About the Authors

Dr. Maghelal is an assistant professor in the Department of Public Administration in the

University of North Texas. His research interest includes transportation planning, GIS, and

healthy communities. He has published several articles related to use and enhancement of public

transit, non- motorized modes of travel in the US. His co-authored article in JAPA won the best

article award in 2007.

Cara Capp is a graduate of School of Urban and Regional Planning at the Florida Atlantic

University. She currently is employed with the clean water organization in Miami FL. Her

research interest includes environmental planning and water resource management.




                                                 31
Acknowledge ments

This manuscript is a part of research funded by the Robert Wood Johnson Foundation through

the active living research dissertation grant round 3. Funding and support provided by the active

living research organization is very much appreciated. Also some of the analysis derives from

the review conducted by Ann Moudon at Washington State University and Chanam Lee at Texas

A&M University. I would like to thank them for sharing their analysis.

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