Frequently Asked Questions
What is retroreflectivity?
Retroreflectivity is a term that is synonymous with the coefficient of retroreflectance, which is formally defined in ASTM E808. In general terms, retroreflectivity describes the efficiency of a material to redirect light back to its source. This is a unique form of the more common diffuse reflection, whereby light is scattered in all directions after striking an object. Retroreflective materials are engineered to redirect most of the light back toward the source, which gives signs and pavement markings a brighter appearance at night from the driver’s perspective.
Motorists experience the benefits of retroreflectivity whenever light from their headlights shines on traffic signs. Signs made with retroreflective sheeting materials appear to glow in the dark, making them easier to see. The legends on retroreflective signs provide important information to motorists as they navigate the nation’s highways, streets, and roads at night.What makes the traffic signs visible at night?
Traffic signs are covered with retroreflective sheeting materials. These materials are usually made with tiny glass beads embedded in plastic or with a very small, complex pattern of cube corners that work like prisms. Both of these types of retroreflective materials redirect light back towards its source, but the performance of the materials varies. Photographs of various sheeting patterns of both types are shown on the Retroreflective Sheeting Identification Guide produced by the Federal Highway Administration (FHWA), which is available at: HTML, DOC 788 KB, PDF 556 KB.
Why is the FHWA concerned about the visibility of traffic signs at night?
One of the FHWA’s primary missions is to improve safety on the nation’s roadways. Approximately 42,000 men, women, and children have been killed on American roads during each of the past eight years. While only one quarter of all travel occurs at night, about half of the traffic fatalities occur during nighttime hours.
During daylight hours, drivers have a number of visual cues, such as shoulders, pavement markings, overhead and post-mounted signs, roadside vegetation, guardrails, fences, and buildings, to make navigation easier. Although factors like intoxication and fatigue also contribute to the disparity between day and night crash rates, it is well known that darkness reduces the visual cues available to the driver. Unless they are illuminated or made from retroreflective materials, the traffic control devices and other visual cues that are readily available to drivers during daylight hours are usually more difficult to see at night.
Adequately maintained retroreflective signs are easier to see at night. The improved nighttime visibility of retroreflective signsheightens motorists’ understanding of the roadway, enhances traffic flow, and has the potential to improve highway safety.
Nighttime visibility of traffic control devices is becoming increasingly important as our population ages. By the year 2020, about one-fifth of the U.S. population will be 65 years of age or older. In general, older individuals have declining vision and slower reaction times. Signs that are easier to see and read at night can help older drivers retain their freedom of mobility and remain independent.
What is the MUTCD?
The Manual on Uniform Traffic Control Devices (MUTCD), which is published by the Federal Highway Administration, defines the standards used by road managers nationwide to install and maintain traffic control devices on all streets and highways. The MUTCD is available at: http://mutcd.fhwa.dot.gov.
What are the current regulations for sign retroreflectivity
The 2003 MUTCD states in Section 2A.08, “Regulatory, warning, and guide signs shall be retroreflective or illuminated to show the same shape and similar color by both day and night.” This standard has remained essentially unchanged for almost 50 years. The 2003 MUTCD also says in Section 2A.22, “To assure adequate maintenance, a schedule for inspecting (both day and night), cleaning, and replacing signs should be established.”
Further impetus for attention to sign visibility resulted from the 1993 U.S. DOT Appropriations Act requiring the Secretary of Transportation to “…include a standard for minimum level of retroreflectivity that must be maintained for traffic signs and pavement markings for all roads open to public travel.” In response to this legislative mandate and after many years of research and proposed rulemaking, the FHWA has developed and adopted a set of minimum retroreflectivity levels for traffic signs.
Revision 2, which became effective in January 2008, adds new provisions regarding sign retroreflectivity to Section 2A.09 of the 2003 MUTCD, as well as a new Table 2A-3, Minimum Maintained Retroreflectivity Levels. Public agencies will have until January 2012 to implement and then continue to use an assessment or management method that is designed to maintain traffic sign retroreflectivity at or above the minimum levels shown in the new Table 2A-3. Public agencies will have until January 2015 to replace any regulatory, warning, or ground-mounted guide (except street name) signs and until January 2018 to replace any street name signs and overhead guide signs that are identified by the assessment or management method as failing to meet the minimum retroreflectivity levels. These new provisions and the new Table 2A-3 can be viewed at the FHWA’s MUTCD website at: http://mutcd.fhwa.dot.gov.
Provided that an assessment or management method is being used, an agency would be in compliance with the requirements of the new provisions in Section 2A.09 even if there are some individual signs that do not meet the minimum retroreflectivity levels at a particular point in time.How can highway officials assure that they are meeting the new provisions for retroreflectivity and that their signs provide reasonable visibility at night?
Since the retroreflective properties of traffic control devices deteriorate over time, highway officials should assess their schedules for inspecting, cleaning, and replacing signs to ensure that these maintenance activities meet the provisions of the MUTCD, and more importantly, the needs of drivers at night. Agencies will need to implement one or more of the five methods described in Section 2A.09 of the MUTCD to assess signs for nighttime visibility, or an agency may decide to develop its own assessment or management method based on engineering studies. Additionally, procurement processes should be checked to ensure that sign materials are being specified that offer retroreflectivity performance that meets or exceeds the minimum levels specified in the new Table 2A-3 in the MUTCD.
Can I use any type of sign sheeting as long as its retroreflectivity meets the minimum specified levels?
The new Table 2A-3 indicates that any type of sheeting including the Type I (commonly called Engineering Grade), Type II (commonly called Super Engineering Grade), or Type III beaded (commonly called High Intensity Beaded) sheeting and the Type III, IV, VI, VII, VIII, IX, or X prismatic sheeting may be used on any sign with the following exceptions: Types I, II, and III beaded sheeting cannot be used for the white legends on overhead guide signs; Type I beaded sheeting cannot be used for the white legends on ground-mounted guide signs; and Type I beaded sheeting cannot be used for the yellow or orange backgrounds on warning and temporary traffic control signs.
Can I still use Type I Engineering Grade sign sheeting?
Type I Engineering Grade sign sheeting may still be used for white, green, and red backgrounds. Type I Engineering Grade sign sheeting also may still be used for the white legend on a sign with a red background. Thus, STOP signs and black-on-white regulatory signs may still be made from Type I Engineering Grade sign sheeting.
However, when agencies review their signing practices and their choice of sign materials, the annualized costs of the signs using factors such as expected sign life should be considered. Even though a particular type of sheeting might initially meet the minimum retroreflectivity levels when it is new, it might quickly degrade to below the minimum retroreflectivity levels, thus losing its effectiveness at night and requiring replacement the next time its retroreflectivity is assessed. The use of higher performance sheeting, even though it has a higher initial cost, might provide a better life-cycle cost for the agency.Can fluorescent colors be used?
Fluorescent versions of sign colors may be used provided that they meet the minimum retroreflectivity levels specified for the basic color. Thus, fluorescent yellow and fluorescent yellow-green signs would need to meet the minimum retroreflectivity levels for yellow signs, and fluorescent orange signs would need to meet the minimum retroreflectivity levels for orange signs.
Why are signs with blue or brown backgrounds excluded from these retroreflectivity requirements?
At the time that the changes associated with Revision 2 were being developed, the research for signs with blue or brown backgrounds had not yet been completed. However, a research report (Publication No. FHWA-HRT-08-029) that provides minimum recommended retroreflectivity levels for brown and blue signs was completed in 2007 and will be available soon.
What information is available to assist in the implementation of the new requirements for minimum sign retroreflectivity?
The FHWA is developing training for Local/Tribal Technical Assistance Programs (LTAP/TTAP). After the LTAP and TTAP representatives have received training, they will be able to assist highway officials to comply with the new provisions in the MUTCD regarding sign retroreflectivity. Also available are:
- A supplemental brochure to the MUTCD language (4-pager)
- An information flyer (tri-fold)
- Informational and Training presentations
- Sheeting ID Guide
- Toolkit for small and medium sized agencies without engineers (coming Summer 2008)
- Newsletters
- Other information such as research reports is available at the following website: www.fhwa.dot.gov/retro.
What sheeting should I use for my agency?
Cost increases from upgrading materials and/or processes might be offset by the long-term savings that result from the longer life of the higher performance sheeting products.
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