Guidelines for Guide Sign Visibility

A frequent dilemma facing highway agencies is deciding how to most effectively provide visible overhead guide signs. There are no guidelines that agencies can reference to help decide how to provide sufficient visibility of overhead guide signs. For instance, it seems that there is a general belief that it is adequate to turn off guide sign lighting in rural areas with flat terrain if highly retroreflective sheeting materials are used. However, there is little consensus in other areas such as suburban and urban areas where the visual background and roadway geometries are more complex. The only official national guidance in the Manual on Uniform Traffic Control Devices (MUTCD), which states <span>"All overhead sign installations should be illuminated unless an engineering study shows that retroreflection will perform effectively without illumination. There are many factors that must be considered such as: (1) capital and maintenance costs of fixed sign lighting; (2) lighting technologies, lighting levels, lighting characteristics (e.g., SPDs); (3) retroreflective sign sheeting materials and colors; (4) visual complexity of the surrounding roadside environment; (5) presence and amount of roadway lighting; (6) traffic volumes; (7) sign position with respect to the approaching traffic; (8) roadway geometry; (9) minimizing unused uplighting; and (10) sign detection and sign legibility. Other influences that need to be considered include vehicle headlamp aim as newer headlamps provide less illumination to overhead guide signs, an increasingly older driver population, mixed vehicle types, sign spacing less than desirable (800') due to closely spaced interchanges, weather such as snow, dew, and fog, etc. Currently, agencies rely on unsubstantiated information or conduct non-scientific nighttime demonstrations with agency personnel. Because of the lack of guidelines, many agencies repeat these efforts in order to make decisions. There is typically little documentation provided and little control over the efforts. Research is needed to develop a set of guidelines that can be used by agencies trying to determine the most effective way to provide visible overhead guide signs (and overhead street name signs). The guidelines should be a comprehensive stand-alone document that agencies can use to assess the visibility of guide signs (and overhead street name signs) with currently available options and future technologies. The guidelines should be independent of material properties and related to luminance or some other measure of visual performance. To the extent possible, the guidelines should be supported with relevant crash data and life cycle costs. To accomplish this objective, the following tasks are recommended: (1) conduct a literature review to document any state or other national guidelines and research regarding guidelines, legislation, policies, and practices regarding efforts to establish guidelines for visible overhead guide signs (including overhead street name signs); (2) assess the available measures of visual performance; (3) draft a summary report of the results of the literature reviews, providing an objective overview of the status of overhead guide sign visibility concerns and considerations, to include a recommended research plan for the second phase of the research that outlines the preliminary guidelines and identified research needs to complete the guidelines; (4) conduct the approved research plan to support the completion of the guidelines, including field testing with full scale signs with and without lighting, sign visibility, sheeting type and the interaction of sheeting type and lighting; (5) develop a metric for assessment of the sign performance; (6) develop recommended guidelines for visible overhead guide signs; and (7) develop a final report with revised guidelines and suggested updates to AASHTO's lighting policies.


  • English


  • Status: Proposed
  • Funding: $600000.00
  • Contract Numbers:

    Project 5-20

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Harrigan, Edward

  • Start Date: 20100613
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 26461

Subject/Index Terms

Filing Info

  • Accession Number: 01463926
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 5-20
  • Files: TRB, RiP, USDOT
  • Created Date: Jan 3 2013 2:32PM