Background: Many state transportation agencies have adopted the use of lead-free yellow pavement markings because of agency policy, legislation, or a U.S. Environmental Protection Agency-imposed mandate. Since switching to lead-free yellow markings, some state highway agencies (including Virginia, Florida, and South Carolina) have noted that these markings may not appear yellow at night. Yet, when analyzed using traditional color-measuring techniques, these materials meet existing requirements for yellow. Additionally, lead-free markings are often more susceptible to fading under ultraviolet exposure, increasing the difficulty of nighttime color recognition. The difficulties associated with recognition of yellow pavement markings represent a potential safety concern.
There has been little previous research to correlate the color specifications of pavement marking materials with driver needs. In December 1999, FHWA issued a Notice of Proposed Rulemaking (NPRM) for Color Specifications for Retroreflective Sign and Pavement Marking Materials (Docket No. FHWA 99-6190). The proposed color specifications are in-service requirements for daytime and nighttime color of markings. In January 2001, American Society of Testing Materials (ASTM) issued Standard Specification D6628-01, which defines the daytime and nighttime colors of pavement markings. These requirements apply throughout the service life. To a large degree, both the NPRM and ASTM D6628 are based on the colors of materials that were used prior to the replacement of lead chromate and may not meet driver recognition needs. When the FHWA Final Rule is issued (as early as mid-2002), transportation agencies may have new requirements for the in-service color of pavement marking materials.
Daytime color measurement of pavement marking materials is commonly used for quality control and materials acceptance. Measured with a "45/0 geometry" (ASTM Standard Test Method E1349), this procedure is not intended to measure the appearance of daytime color of pavement markings. Daytime luminance (Qd), measured at "30-m geometry," is used by the European Union to describe performance. Nighttime color measurements (ASTM Standard Practice E811) are limited to the laboratory environment. Recently, a field instrument was developed that provides the capability to measure the nighttime color of pavement markings. However, an evaluation of how well this procedure correlates with the perception of color by a driver has not been conclusively determined.
There is a need for research to assess driver needs for color recognition, whether existing pavement markings meet those needs, and the material properties that will provide effective color. The anticipated products from this research will include recommended color specifications and field measurement procedures for pavement marking materials that are linked to driver needs. This research will result in greater correlation between field measurement techniques and color performance of pavement marking materials.
Objective: The objective of this research is to develop recommendations on day and night color limits to assist agencies in properly specifying materials and in characterizing color to achieve satisfactory performance. In developing these recommendations, it will be necessary (1) to identify the relationship between material specifications and color appearance, (2) to determine the characteristics that allow drivers to accurately distinguish between yellow and white markings for both day and night, and (3) to determine if the color of existing pavement marking materials in the field meet driver needs.
Tasks: Accomplishment of the project objective(s) will require at least the following tasks.
(1.) Conduct a literature review to obtain the latest information on pigment technology, color perception, related instrument technology, and color measurement techniques for pavement marking materials. Survey state transportation agencies to determine the current usage, specifications, and testing methods. Survey manufacturers of pavement marking materials and pigments for current technology. (2.) Conduct a human factors evaluation of driver recognition of pavement marking color. The evaluation should address drivers' ability to clearly and quickly distinguish between white and yellow beaded pavement markings both day and night. The evaluation should consider the impacts of luminance, hue, saturation, and color contrast on color recognition. For nighttime conditions, the evaluation should be conducted under low ambient lighting using a tungsten-halogen source. (3.) Develop a test plan for conducting field measurements of the color of existing pavement marking materials. Both yellow and white markings shall be measured, with an emphasis on yellow markings. Measurements should be made in a minimum of 4 different states, with different climatic conditions. Proposals should identify the states where measurements will be made. Nighttime color measurements shall be made with a "30-m geometry" instrument. Daytime measurements shall be made with "45/0 geometry" and "Qd " instruments. At a minimum, each measurement shall include the type of material, age, and AADT. The total sample of all measurements should represent a variety of thermoset, thermoplastic, and paint materials, and a range of marking material ages. The proposed sample size should be sufficient to ensure statistical validity. (4.) Prepare an interim report summarizing the results of Tasks 1 and 2 and outlining the test plan for Task 6. The interim report should explain the underlying phenomena of recognition of nighttime color of yellow markings, including a discussion of pigment type, formulation, illuminant characteristics, and bead application. (5.) Meet with the NCHRP panel to review the Task 4 interim report, approximately 1 month after its submittal. Submit a revised interim report addressing the panel's review comments.(6.) Conduct the test plan for the field measurements of the color of existing pavement marking materials. ( 7.) Analyze the data from Task 2 and Task 6 to determine whether the colors of existing pavement markings in the field meet driver color recognition needs. Investigate the relationship between the measured materials and their color performance to assist agencies in developing pavement marking specifications that will provide adequate color recognition. (8.) Develop recommendations on day and night color limits and field measurement procedures. These recommendations may ultimately lead to updates of ASTM and American Association of State and Highway Transportation Officials (AASHTO) standards and may result in a new procedure for field measurement of color. (9.) Submit the final report documenting the entire research effort. The final report shall describe how the project was conducted including recommended field measurement procedures and recommended revisions to standards as appendices.
Status: The project has been completed. Research Results Digest 328 summarizes the project. The complete report is available on TRB's website as NCHRP Web-Only Document 125.
Product Availability: Research Results Digest 328