U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590

Skip to content


eSubscribe Envelope

FHWA Home / Safety / Roadway Departure / Methods for Maintaining Traffic Sign Retroreflectivity

Methods for Maintaining Traffic Sign Retroreflectivity

November 2007
Publication No. FHWA-HRT-08-026

< Previous Table of Contents Next >


Traditionally, it has been up to Federal, State, and local agencies to manage and maintain their traffic signs in accordance with the MUTCD standards. As a result, agencies have implemented different methods to manage traffic signs that reflect local conditions, needs, and priorities. The management process begins with agency policies and practices regarding the use of retroreflective materials in the fabrication of new signs. Agency policies have often been driven by the costs of the various retroreflective materials. Once new signs have been deployed, there has been less attention paid to the adequacy of the retroreflectivity provided by an individual sign. By and large, the most common method used to trigger maintenance of traffic sign retroreflectivity has been visual inspection. However, other methods have been tested and implemented including measurement of retroreflectivity and scheduled replacements based upon sign age.

The establishment of minimum maintained traffic sign retroreflectivity levels in the MUTCD requires that agencies adopt one or more acceptable methods. This provision was intended to assure that agencies use methods that will be effective in maintaining nighttime visibility for their deployed traffic signs. This minimum standard has raised concerns among State and local agencies.

One of the main concerns is associated with the potential increase in tort exposure once numerical values are tied to minimum retroreflectivity levels for traffic signs. In 1998, a national survey was conducted asking if agencies expected “an increase in tort claim lawsuits as a result of the minimum retroreflectivity values.”(10) Two-thirds of the respondents replied that their agencies did expect an increase in tort claim lawsuits if minimum retroreflectivity levels for traffic signs were implemented. The survey respondents claimed that “whether the retroreflectivity contributed to the accident or not, the lawyers will be aware of the minimum values and will use them against the State.”

In order to minimize the risk to an agency of being found negligent in meeting the requirements for minimum traffic sign retroreflectivity, a sign maintenance program must be provided in order to ensure the nighttime visibility of signs. This approach has been effective in related tort claims against agencies. Conducting and maintaining an inventory of devices, replacing devices at the end of their effective lives, knowing the laws relating to traffic control devices, and applying State traffic control device specifications and standards are four basic principles suggested by the ITE Traffic Sign Handbook to “significantly reduce tort liability lawsuits involving traffic control devices.”(11) It follows that sign maintenance methods need to be developed and implemented to provide protection from tort liability.

There have also been concerns that the implementation of new methods would impose new burdens on agencies. It was noted that the MUTCD should provide flexibility for agencies in terms of complying with minimum maintained traffic sign retroreflectivity levels.

This need for maintenance methods was cited often during the FHWA sponsored workshops on minimum levels of in-service retroreflectivity for signs in the summer of 2002.(12) These workshops were conducted to present the most recent research findings on minimum levels of retroreflectivity and to solicit input from public agency officials prior to developing a proposed rule on minimum levels of retroreflectivity. A total of 99 individuals participated in the four invitation-only workshops. One of the most consistent key findings of the workshops was that the public agency participants wanted the MUTCD to provide several methods that could be used to meet the minimum retroreflectivity requirements.


A significant portion of the 2002 FHWA workshops on nighttime traffic sign visibility was devoted to discussions of options that are available to agencies to improve the nighttime visibility of signs. Several different terms were used to describe the options, including evaluation methods, assessment procedures, implementation options, and management processes. All of the terms were intended to describe actions that an agency can take to provide a reasonable level of nighttime sign visibility to road users.

There was essentially unanimous agreement among the public sector participants that the MUTCD should not dictate the methods or processes to be used to determine whether signs meet the goal of reasonable nighttime visibility. Instead, the MUTCD should describe various evaluation methods that agencies can choose from to provide reasonable nighttime sign visibility. The ability to choose from several options will allow agencies to adopt a method that best fits the resources and current practices of individual agencies.

Different methods were presented and discussed during the various workshops. Most methods can be divided into one of two categories—evaluation or management methods. Evaluation methods involve some type of assessment of the nighttime visibility of individual signs (e.g., visual inspection or retroreflectivity measurement). Management methods are based on the expected retroreflective life of the overall sign inventory, based on factors such as warranties, demonstrated performance, or control sign assessments. The following accepted methods are described in greater detail in this report.

Other methods (e.g., sample comparisons, Q-beam methods (illuminating a sign with a spot light during a daytime visual inspection), and visual inspection techniques tied to evaluation distances dependent on sign type and size) were identified in the workshops but were not considered practical or effective in determining the adequacy of nighttime visibility. Workshop participants also indicated that a sign management system could also be used as one of the evaluation methods. However, an evaluation method is a tool that supports a sign management system. A sign management system does not provide a means for evaluating nighttime sign visibility; it provides a means of managing information from one or more evaluation systems used to predict when a sign should be replaced.

The MUTCD minimum retroreflectivity requirements are not intended to imply that agencies must measure the retroreflectivity of every sign in their jurisdictions. The various maintenance methods provide agencies with options that will improve nighttime sign visibility.

The sign retroreflectivity maintenance methods described above are divided into two groups, assessment methods and management methods, as noted in table 3. Agencies have flexibility to adapt these methods for maintaining sign retroreflectivity into existing sign management processes or may upgrade their sign management process by incorporating an approved maintenance method.

Table 3. Retroreflectivity Maintanence Methods.
Assessment Methods Management Methods
Nighttime Visual Inspections
Retroreflectivity Measurements
Expected Sign Life
Blanket Replacement
Control Signs


Combinations of two or more methods may be viable for some agencies. In addition, agencies are not limited to the proposed maintenance methods. Agencies may develop their own methods using documented engineering studies that demonstrate that deviations are appropriate.

Agencies may combine different methods or parts of different methods to achieve sign retroreflectivity maintenance practices that best fit the agency’s needs and budget. Generally, a combination method would include a management method complemented with an assessment method used to provide supplemental data. This method provides a means to track individual signs but without the need to inspect or measure every sign. Any number of combinations can be implemented to logically integrate with other aspects of the sign management process and best fit an agency’s limited resources. Also note that the proposed methods can be used exclusively with effective results.

One possible combination is the use of a management method with both daytime and nighttime visual inspections. The expected life of a sign is a management method and is based on the age and degradation of the sheeting types used. This management method in combination with daytime visual inspections may allow an agency to track how many signs they have, how old they are, and where they are located. It also provides field crews with a list or summary of deployed signs that can be easily used to note the need for sign replacements or repairs when conducting nighttime visual inspections. The information may be downloaded to electronic devices (e.g., laptop computers or PDAs) to further facilitate field inspections and documentation of sign conditions and replacement needs. Combining the expected sign life management method with both daytime and nighttime visual inspections is one example of adapting methods that meet an agency’s needs.

Another possibility is to combine expected sign life with measured retroreflectivity. Under this method, it is not required to measure the retroreflectivity of all signs. Measurement of a small sample from across a region allows the agency to compare the expected and measured retroreflectivity. The measurements allow the agency to validate, and revise if necessary, the service life of each sign sheeting material and color used by the agency.

In summary, these methods can be used in different ways but will provide a consistent evaluation of the nighttime visibility of in-place traffic signs. Additional details on these methods and their applications are provided in the following chapters.


The intent of the methods is to provide a systematic means for agencies to maintain traffic sign retroreflectivity at or above the minimum levels. The FHWA has determined that agencies that use an approved method to maintain traffic sign retroreflectivity are in conformance with the minimum maintained retroreflectivity requirements established in the MUTCD.

Substantial conformance with the MUTCD Section 2A.09 is achieved by having a method in place to maintain the minimum retroreflectivity levels. Conformance does not require or guarantee that every individual sign will meet or exceed the minimum retroreflectivity levels at every point in time. For example, if an agency chooses to implement the visual nighttime inspection method, there is no guarantee that the retroreflectivity of all signs will be satisfied during the entire period that the signs are in service. Assuming that an agency successfully completes the annual visual nighttime inspections and that signs failing the subjective evaluation or signs rated as marginal are scheduled for replacement or reassessment within a reasonable time period, then there is clearly a period of time when these signs might be below the minimum retroreflectivity levels while the sign is awaiting replacement or reassessment. Having a method in place to maintain the minimum retroreflectivity levels is a valuable way for agencies to prioritize how to spend limited resources on those signs that should be replaced sooner, ultimately contributing to improved safety for the motoring public.

There are other conditions where signs might be rated as being satisfactory while temporarily falling below the minimum retroreflectivity levels. For example, dew and frost on signs have been shown to significantly reduce retroreflectivity.(13) In addition, while research has shown that the visual nighttime inspection is a reasonable method in terms of identifying signs that need to be replaced because of marginal retroreflectivity, the nighttime visual inspection method is no 100 percent reliable.(14,15) When sign inventories are not available for use during visual inspections, it is not unreasonable to miss a small percentage of signs along a densely-signed corridor, especially if a sign was knocked down or missing for some other reason at the time of the inspection. It is also possible that a sign or a group of signs meets the retroreflectivity minimums for a predetermined number of years, but because of factors such as manufacturing defects or inadvertent mishandling during installation, a certain percentage might fall below the minimum retroreflectivity levels sooner than expected.

Regardless of which maintenance method is adopted by an agency, documentation of the sign management process is important in assisting agencies to achieve conformance with the MUTCD standard to maintain minimum retroreflectivity levels of traffic signs. Written procedures ensure that agency personnel properly follow the selected method, while maintenance records provide the agency with a systematic process for sign replacements and justification for the allocation of limited resources. As an example, measurements of traffic sign retroreflectivity might show that certain signs are near or below the thresholds in the table of minimum retroreflectivity levels even before they reach the end of their expected life. The records provide documentation that an appropriate maintenance method was followed and permit the agency to assess and revise, if necessary, the method for a given type or group of signs. As long as an agency has a reasonable method in place to manage or assess its signs and establishes a reasonable schedule for sign replacement as needed, the agency will be deemed to be in conformance.

< Previous Table of Contents Next >
Page last modified on October 17, 2012.
Safe Roads for a Safer Future - Investment in roadway safety saves lives
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000