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Appendix E: Guidelines for Traffic Impact Reports/Studies


The installation of a traffic signal should be based on a comprehensive traffic engineering study that examines all aspects of the intersection. The study should examine other control alternatives and carefully weigh the benefits and detriments of signalization.

An initial part of the study may be a comparison of the site parameters (i.e., volumes, accidents) and the warrants listed in the MUTCD. However this may not be considered a comprehensive study. Satisfying one or more warrants alone does not justify a signal. A comprehensive study should be performed to determine whether or not a signal will improve overall safety and/or operation at the intersection.

A comprehensive study for the need of signalization should include but not limited to the following:

  1. Site Description
    • Urban, rural, residential, commercial, etc.
    • General physical layout - curves, skew, grades, etc.
    • Geometrics (Condition Diagram)
      • North arrow
      • Number of lanes (width)
      • Lane designation or use if not marked or signed
      • Channelization/Median
      • corner radii
      • Sight line
      • Ped facilities
      • Nearby development (Firehouse, schools, Railroad etc.)
      • Existing traffic control device
      • Nearby traffic signals
      • Speeds (posted and prevailing)
      • Driveways
  2. Traffic Volumes
    • Recent 12 hour turning movement counts (Not older than 1 year)
    • Anticipated growth
    • Trucks
  3. Operations
    • Field observations
    • Delay
    • Hazards
    • System needs
  4. Safety
    • Recent accident data (3 year)
    • Field observations
  5. Impacts of Signalization
    • Improve safety and/or operation?
    • Delay
    • Storage areas (queuing)
    • Nearby signals spacing
    • Traffic signal system (how will this signal fit?)
  6. Alternate Solutions (no signal)
    • Type of solution
    • Impacts to adjacent intersections
    • Safety
    • Delay
  7. Alternate Solutions (in lieu of signal)
    • Roundabout
  8. MUTCD Warrants
    • Are warrants met? (which one or combination)
  9. Recommendation
    • Signalization (explanation)
    • No signalization (explanation)
NOTE: (PDF, 79 kb) There may be other sources/handbooks such as Institute of Traffic Engineers that can be used as guides when performing a study.
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