USA Banner

Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation
FHWA Highway Safety Programs


Below are several research documents that you may find useful in learning more about sign retroreflectivity.

  • Daytime Color Appearance of Retroreflective Traffic Control Sign Materials [HTMLPDF 1.15MB]
    This report describes a research study conducted to determine physical measurements of the chromaticity and luminance of retroreflective sign materials by means of instruments and to determine perceptual measurements of the color appearance (hue, apparent saturation, and brightness) of these materials as judged by a group of human observers. Comparisons are presented between physical measurements made in the laboratory and in the field and between these physical measurements and the psychophysical determination of color appearance obtained from a sample of 17 observers. [Publication No. FHWA-HRT-13-018]

  • Minimum Retroreflectivity Levels for Blue and Brown Traffic Signs [HTMLPDF 1MB]
    This report provides research findings supporting recommendations for minimum maintained retroreflectivity (MR) levels for white-on-blue and white-on-brown signs. The report also includes findings of an investigation of MR levels needed for complex visual conditions, such as glare from oncoming headlamps and fixed roadway lighting. [Publication No. FHWA-HRT-08-029]

  • Minimum Retroreflectivity Levels for Overhead Guide Signs and Street-Name Signs [HTMLPDF 837 KB ]
    This 2003 report prepared for the FHWA by Texas Transportation Institute presents the results of a study that investigated the nighttime visibility needs of drivers for viewing overhead guide sign and street name signs. [Publication No. FHWA-RD-03-082]

  • Updated Minimum Retroreflectivity Levels for Traffic Signs [HTMLPDF 837 KB]
    This 2003 report prepared by Texas Transportation Institute for the FHWA updates the minimum levels of traffic sign retroreflectivity for certain types of traffic signs (regulatory, guide, and warning), which were originally generated in 1993. [Publication No. FHWA-RD-02-081]

  • Maintaining Traffic Sign Retroreflectivity: Impacts on State and Local Agencies [HTMLPDF 417 KB]
    This 2007 report prepared by the FHWA's Turner Fairbank Highway Research Center analyzes the administrative, fiscal, implementation, and tort liability concerns of State and local transportation agencies in relation to the adoption of minimum maintained retroreflectivity levels for traffic signs. The results are based on input received at four workshops held during the summer of 2002. [Publication No. FHWA-HRT-07-042]

  • Workshops on Nighttime Visibility of Traffic Signs: Summary of Workshop Finding [HTML]
    This report presents the results of four workshops sponsored by the FHWA in 2002 to obtain input from stakeholders regarding the issues and alternatives associated with minimum levels of in-service sign retroreflectivity. About 100 invited representatives attended the workshops, including city, county, and State transportation agencies, professional organizations, agency attorneys, and FHWA staff. [Publication No. FHWA-SA-03-002]

11th Edition of the MUTCD coverpage

For information about traffic control devices and the Manual on Uniform Traffic Control Devices (MUTCD), other than visibility or retroreflectivity, please see FHWA's MUTCD website