traffic signals REV2 by jbw10297


									 How to determine if an
                                                 A                                             Traffic
                                                        properly placed traffic signal can
                                                        improve the flow of traffic and
 intersection is right for                              decrease crashes. An unnecessary
                                                 one can be the source of danger and

    a traffic signal...                          annoyance to all who use the intersection,
                                                 including pedestrians, bicyclists and
A careful analysis of traffic operations is      motorists.
necessary to determine the need for a
traffic signal. Roadway authorities take         For more information about traffic signals
this information into consideration:             in your area, contact your ODOT Regional
  • Does the number of vehicles on               office, or ODOT’s Traffic Engineering and
      intersection streets cause conges-         Operations Section.
  • Is traffic on the main street so                    Region 1 - (503) 731-8200
      heavy that drivers on the side              (Portland metro and surrounding area)
      streets will try to cross when it is
                                                        Region 2 - (503) 986-2600
      unsafe? Have crashes resulted from
                                                       (Salem, Mid Willamette Valley
      this condition?
                                                             and North Coast)
  • Have less restrictive traffic controls
      been tried and found inadequate to               Region 3 - (541) 957-3656
      address the problem (such as                (Roseburg, Southern Willamette Valley
      warning signs, stop signs, flashers,                  and South Coast)
                                                        Region 4 - (541) 388-6180
  • Is pedestrian traffic heavy? If so, is
                                                        (Bend and Central Oregon)
      the street they are trying to cross a
      wide, high speed and busy street?                 Region 5 - (541) 963-3177
  • Does the number of schoolchildren                 (Pendleton and Eastern Oregon)
      crossing the street require special
      controls? If so, is a traffic signal the
      best solution?
  • Will the installation of a signal allow
      for a smooth flow of traffic with a
      minimum number of stops, thereby
      reducing overall congestion?
  • Does the crash history indicate that
                                                        TRAFFIC ENGINEERING
      a signal will reduce the number of
                                                      AND OPERATIONS SECTION
                                                   Oregon Department of Transportation
                                                       355 Capitol St. NE, 5th Floor
The nationally accepted standards for
                                                         Salem, OR 97301-3871
traffic signals, stop signs and other
                                                         Phone: (503) 986-3568
traffic control devices are contained in a
publication called “The Manual on Uni-
                                                          Fax: (503) 986-4063
                                                                                              Myth and Reality
form Traffic Control Devices.” It is used                                                      A tool to help motorists,
by transportation officials around the
country, including ODOT, to evaluate                                                           bicyclists and pedestrians
whether or not a traffic signal or other
measure is needed in a specific location.
                                                                                            alternatives to a traffic signal including:
                        Learning About Traffic Signals                                      • revising warning signs;
                                                                                            • improving sight distance;

T   raffic signals are such a common
    part of everyone’s day, we often
forget just how important they are.
                                              safety and efficiency of vehicle, bicycle
                                              and pedestrian traffic.
                                                                                            • reducing speed on approaches;
                                                                                            • revising intersection geometry;
                                                                                            • restricting turning movement;
                                              Improper or unjustified signals can
The Oregon Department of Transpor-            result in one or more of the following:
                                                                                            • installing all-way stop control; and
tation encourages you to learn more                                                         • installing a roundabout.
                                              • Significant increases in the frequency
about the advantages and disadvan-               of some types of collisions (espe-         The intent of the engineering study is to
tages of traffic signals and how trans-          cially rear-end collisions);               identify the safest and most efficient
portation experts determine where —                          • Increased congestion,        form of traffic control to use for that
and where not — to place signals.                              air pollution, and fuel      particular location.
                                                             • Excessive delay;             What happens once the traffic
    Advantages of Traffic Signals                            • Excessive disobedience       signal is justified?
Traffic signals help control the flow of                       of the signal indications;
                                                                                            If a signal is approved for a state high-
vehicles, pedestrians and bicycles by                          and
                                                                                            way, then it may be scheduled for
giving “right-of-way” to the various                         • Increased use of less
                                                                                            construction as funds become available.
movements in an orderly manner.                                adequate streets as
                                                                                            The design plans are developed and
Signals that are properly located, de-                         motorists attempt to
                                                                                            reviewed, and public meetings may be
signed and maintained can:                                     avoid the traffic signals.   held. Once the plans are completed, the
• Provide for orderly movement of                                                           signal project is put out for bid and
   traffic;                                                   Frequently Asked              awarded to an electrical construction
• Increase capacity of the intersection;                                                    contractor.
• Reduce frequency and severity of                                Questions
                                                                                            How much does a signal cost?
   certain types of crashes, especially                        … and Answers!
   right-angle collisions;                                                                  A typical traffic signal installation costs
• Provide for continuous movement of          How does ODOT determine where                 more than $150,000. This includes
   traffic at a definite speed along a        traffic signals are installed?                some cost for miscellaneous items such
   given route; and                                                                         as sidewalk repair, pedestrian access
                                              ODOT installs and operates traffic
• Interrupt heavy traffic at intervals to                                                   ramps and pavement markings, which
                                              signals in accordance with the Manual
   permit other vehicles or pedestrians                                                     are often required for a new signalized
                                              on Uniform Traffic Control Devices, a
   to cross.                                                                                intersection. Annual maintenance and
                                              national standard developed to ensure
Overall, traffic signals help us get                                                        power costs of about $4,000 also must
                                              uniformity in the application and design
where we’re going safely and in a                                                           be considered.
                                              of traffic signals, signs and pavement
timely manner.
                                              markings throughout the country.              How is a study for a new signal on
                                                                                            a state highway requested?
  Disadvantages of Traffic Signals            Following the guidance of the MUTCD,
                                              a study is performed on the potential         A written request must be made to the
Traffic signals are sometimes consid-         placement of a traffic signal by looking      ODOT Region Traffic Manager. See
ered a “cure-all” for problems at inter-      at traffic volumes, pedestrian charac-        contact information on the back of this
sections. In fact, traffic signals that are   teristics, crash history, and physical        brochure.
poorly located can adversely affect the       characteristics of the location.
                                              The study may investigate a range of

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