The National Academies

NCHRP 05-15 [Completed]

Visibility Performance Requirements for Vehicular Traffic Signals

  Project Data
Funds: $350,000
Research Agency: Westat, Inc.
Principal Investigator: Mark Freedman
Effective Date: 3/18/1996
Completion Date: 12/31/1999

Objectives: The objectives of this research project were to develop visibility performance requirements for vehicular traffic signals that are independent of light source and to develop practical, reliable, and economical test methods to verify compliance with the performance requirements. The performance requirements shall be based on the visibility needs of the driving population and shall consider the special needs of older drivers and those with color-deficient vision.

Status: The project is completed. The revised report was received in August 2001 and has been delivered to the Institute of Transportation Engineers for their consideration in revising their standards.

Background: The Institute of Transportation Engineers (ITE) standard, Vehicle Traffic Control Signal Heads, is routinely used across the United States for purchasing traffic signal heads. The light intensity and distribution requirements in this standard were established approximately 50 years ago based on the capabilities of traffic signals at that time. Visibility performance requirements are needed that are based on driver needs rather than hardware capabilities.

Tasks: Accomplishment of the project objectives will require the following tasks: (1) Review relevant domestic and international performance data, research findings, and other related information to determine the factors that affect traffic signal visibility, conspicuity, and recognition. These factors may include driver visibility needs; light intensity, distribution, and chromaticity; signal placement, orientation, viewing angle, and axial alignment; ambient lighting levels; sun phantom; and background complexity. (2) Based on the Task 1 review, prepare and submit a working paper recommending chromaticity requirements for red, yellow, and green traffic signal indications. In developing the recommendations, the contractor should consider the capabilities of different light sources, the impact on existing installations, and the needs of drivers with color-deficient vision. (3) Assess the scope and validity of the information reviewed in Task 1, determine the research needed to develop the visibility performance requirements, and develop an experimental plan consistent with the project budget and schedule that addresses these research needs. It is expected that the research needs will include the needs of older drivers and the intensity required at night. The experimental plan should emphasize field experiments and may include laboratory experiments, analytical studies, and computer simulations. The plan should describe in detail the experiments to be conducted, their sequence, and the analysis and interpretation of the data gathered. Limited pilot tests may be conducted to determine the viability of the plan. The experimental plan should focus on 300-mm (12-in.) circular and arrow indications and 200-mm (8-in.) circular indications in red, yellow, and green that are located and used in accordance with the Manual on Uniform Traffic Control Devices. The chromaticities of the three colors should be based on the Task 2 working paper recommendations. (4) Prepare an interim report on the information developed in Tasks 1 through 3 with a revised budget and work plan for Phase II. NCHRP review and approval of the interim report will be required before proceeding with work on the remaining tasks. The contractor should anticipate meeting with the project panel to discuss the interim report and subsequent tasks. (5) Carry out the experimental plan developed in Task 3 and summarize the findings. (6) Based on a thorough analysis of the existing work and the data collected in Task 5, develop the visibility performance requirements for each of the traffic signal indications listed in Task 3. Document the rationale used to determine the performance requirements. (7) Develop test methods suitable for use in the traffic signal shop environment to verify the compliance of traffic signals with the performance requirements. (8) Prepare a final report that documents the entire research effort. The report should include a discussion of how the performance requirements and test methods could be incorporated into the procurement process for traffic signal heads.


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