Waging the minimum

April 2, 2018
FHWA advances rulemaking on levels of traffic sign retroreflectivity

About the author: Opiela is a highway research engineer for FHWA, TFHRC.


The efforts of the Federal Highway Administration (FHWA) Office of Safety and Safety R&D Group has led to the posting of a Notice of Proposed Rulemaking (NPRM) in the Federal Register (Vol. 69, No. 146). This NPRM represents the culmination of many years of efforts to determine minimum levels for traffic sign retroreflectivity and develop methods to bring in-place signs into compliance. The NPRM provides the opportunity for public review and comment on the proposed changes to the MUTCD to implement the minimum levels. The closing date for comments is Feb. 1. All comments will be reviewed and FHWA will make decisions on whether and how to proceed with rulemaking.


Since the early 1990s, the FHWA has sponsored several efforts to promote improvements in the night visibility of traffic signs. At night, road users cannot see as many visual cues as they can in the day and must depend on their headlights to illuminate signs and pavement markings to safely and efficiently navigate the roadway. To provide nighttime sign visibility, most signs are made from retroreflective sheeting. Retroreflectivity is the property of a material to redirect light back toward the originating source. It is a convenient metric for quantifying the night visibility of traffic signs.

The option of making signs “reflective” can be noted as far back as the 1935 Manual of Uniform Traffic Control Devices (MUTCD), but there has never been a measure that defines how reflective signs need to be to meet driver needs.

FHWA research over the past 15 years has advanced, validated and refined the concept of minimum maintained sign retroreflectivity. Initial minimum retroreflectivity levels were first proposed in a 1993 research report. These levels were revised in 1998 through further research. Research supported by FHWA’s Safety R&D Group at the Turner Fairbank Highway Research Center (TFHRC) over the last four years has expanded the proposed minimum levels to overhead and street names signs and fully updated the minimum levels to reflect current conditions. More specifically, the minimum levels were recomputed to consider the effects of various changes, including:

  • Changes in the vehicle fleet to reflect that a large proportion of the fleet is now SUV- or light-truck-type vehicles with higher headlight positions and driver eye heights;
  • Improvements in headlight technology and changes to the “European designs” that reduce the amount of light projected upward;
  • An increasingly older driver population with diminished night visual acuity;
  • Modifications in the MUTCD legibility criteria; and
  • Changes in the characteristics and types of sign materials available.

An acceptable job

The resulting minimum levels are presented in the NPRM. It is important to note that the proposed table of levels represents a significant simplification of the minimum levels tables that were promulgated in the mid-1990s to address concerns expressed by the American Association of State Highway & Transportation Officials (AASHTO).

Since the minimum levels for individual traffic sign retroreflectivity need to be applied over all existing signs, the rulemaking efforts have defined acceptable methods. Methods to maintain traffic sign retroreflectivity can be divided into two groups: assessment methods and management methods. Assessment methods involve the actual evaluation of individual signs by periodic inspections or measurement of each sign. These methods to some degree simply extend the requirements for periodic sign inspections already in the MUTCD. Management methods involve tracking and predicting the retroreflectivity life of signs using sign databases, date labeling, control signs or blanket replacement programs. The various methods allow agencies the flexibility to select methods that can function within their unique sign management processes.

The minimum retroreflectivity levels and methods were developed with significant effort by FHWA to assure their practicality and cost-effectiveness. To assess agency concerns, workshops were held in 1996 and 2002 to describe the minimum levels concept and demonstrate the implications of these levels on driver night visibility. Participant feedback was used to review the proposed minimum levels, evaluate the methods, define training needs and formulate means to facilitate implementation. A training program has already been developed and offered to LTAP centers. In addition, an impacts analysis was undertaken by FHWA to review the fiscal concerns identified during the workshops. These analyses indicated that while it is likely there will be increased costs for sign face materials, the overall increases in costs to agencies would be low if the upgrades were made as part of planned sign maintenance cycles.

The proposed rule will implement the minimum levels and acceptable methods through changes to the MUTCD. Under the proposed implementation plan agencies will have seven years to bring their sign systems into compliance with the provisions that will be added to MUTCD.

Efforts continue at FHWA to develop and administer training on traffic sign retroreflectivity and to develop detailed methods and procedures for assessment and management of retroreflectivity for the millions of in-place signs on the nation’s highways. Planned research includes further efforts to determine a more appropriate standard viewing geometry, develop tools to allow more rigorous analysis of specific sign design and deployment and to define minimum levels for blue and brown signs.

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