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Publication Number: FHWA RD-03-081
Date: June 2003
Updated Minimum Retroreflectivity Levels
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FHWA RD-03-080 - Final Report Summary
The development of minimum levels of retroreflectivity (end-of-service-life values) for traffic signs is one of the latest steps in the evolution of providing a safe and efficient road transportation system. The progression of this concept in the United States was significantly accelerated in 1984 when the Center for Auto Safety petitioned the Federal Highway Administration (FHWA) to establish retroreflectivity standards for signs and markings.(1) In 1993, Congress required the Secretary of Transportation to revise the Manual on Uniform Traffic Control Devices (MUTCD) to include "a standard for a minimum level of retroreflectivity that must be maintained for pavement markings and signs that apply to all roads open to public travel." (2) In 2000, when FHWA revised the MUTCD, a new section (Section 2A.09) was introduced in Part 2, which stands as a placeholder for minimum retroreflectivity (MR) standards for traffic signs.(3)
MR levels help increase nighttime safety because they are a measurable surrogate for providing and maintaining adequate nighttime visibility. MR levels account for such factors as vehicle type, headlamp design, drivers' visual capabilities, roadway type, traffic speed, and the necessary maneuver as dictated by a sign message.
For at least the past two decades, FHWA has been working toward the development of MR levels for traffic signs.(4-8) Recommended MR levels for warning, regulatory, and guide signs were first published in 1993; they were revised in 1998, and then expanded to include overhead guide signs and street-name signs in 2001.(9-13) The development of these previously recommended levels has been based on a headlamp-beam pattern that represents vehicle designs from the mid- to late-1980s. Vehicle headlamps have changed significantly since then. There have also been other significant changes that have prompted the need to update the MR levels for traffic signs before FHWA initiates rule making.
This report includes an updated set of MR levels for traffic signs based on recent developments in vehicle headlamps, vehicle types/sizes, drivers' nighttime needs, and newer sheeting materials. The updated MR levels are also based on more robust computer modeling of retroreflective sheeting performance. The MR levels presented in table 1 represent the result of these updates and the results of various decisions made regarding American Association of State Highway and Transportation Officials' (AASHTO's) policy resolution on MR levels (appendix A). The MR levels presented in table 1 also represent the input from the participants of the four national MR workshops.(14) Although the levels presented in table 1 are subject to change, they represent the most current research recommendations.