History of Sign Retroreflectivity
Since the first edition of the MUTCD in 1935 the manual has required signs to be visible at night by using reflective elements in the sign face. The 2003 Edition of the MUTCD continues to address the visibility of signs. Sign retroreflectivity is specifically addressed in Section 2A.08 Retroreflectivity and Illumination, which states, “[r]” egulatory, warning, and guide signs shall be retroreflective or illuminated to show the same shape and similar color by day and night, unless specifically stated otherwise in the text discussion in the Manual of a particular sign or group of signs. This language has essentially remained unchanged since 1971. However, not until this rulemaking have the methods to assess retroreflectivity levels been established. These assessment methods are necessary to address the degradation of sign retroreflectivity over time.
In the FY 1993 DOT Appropriations Act, the Congress directed the Secretary of Transportation to revise the MUTCD to include a standard for minimum levels of retroreflectivity. Even before then in the mid 1980s the FHWA focused attention on retroreflectivity and visibility of traffic signs. Initial minimum retroreflectivity levels were developed in 1993 and documented in “Minimum Retroreflectivity Requirements for Traffic Signs”, Technical Report, FHWA-RD-93-077. The FHWA has continuously worked to develop minimum maintained retroreflective levels for signs, and assessment and management methods and technologies for the evaluation of traffic signs. The proposed minimum retroreflectivity levels were updated to account for changes in vehicle headlight attributes (i.e., brighter, but with a different illumination pattern), the vehicle fleet mix (i.e., the large number of SUVs has increased the average headlight and driver eye heights), the capabilities of an increasingly older driver population, the changes to sign legibility requirements in the 2000 MUTCD, the needs for overhead guide and street name signs, and the emergence of new sign materials since the 1993 research. These research efforts were completed in 2003, and have become the basis for the minimum maintained traffic sign retroreflectivity rulemaking.
In December 2007, the final rule was published in the federal register, making the sign retroreflectivity requirements a federal regulation effective January 2008. In addition they are incorporated into the second revision of the 2003 MUTCD.
