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Publication Number: FHWA-HRT-07-042
Date: April 2007

Maintaining Traffic Sign Retroreflectivity: Impacts on State and Local Agencies

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4. Previous Impact Analyses

There have been two previous reports on the national impact of implementing minimum maintained levels of traffic sign retroreflectivity: an effort by the National Cooperative Highway Research Program (NCHRP) focused on determining how stringent the requirements could be; and a study undertaken by the FHWA to evaluate the impact on State and local agencies that would be incurred to establish the minimum levels proposed in FHWA-RD-97-052.12 In addition, there are some documented efforts by State Departments of Transportation (DOTs) to assess the impacts of the proposed new minimum levels on their agencies. These studies and reports have taken different approaches, and all provide information on possible impacts. The findings of these efforts are described below. Since the specific proposed minimum levels have not varied greatly, the findings of these previous efforts are believed to be relevant.

4.1. NCHRP Report 346

NCHRP Report 346, "Implementation Strategies for Sign Retroreflectivity Standards,"13 investigated the impacts of alternative implementation strategies for compliance with minimum maintained traffic sign retroreflectivity levels. Two sets of acceptance criteria were considered, with implementation time frames ranging from 1 to 10 years. A cost impacts model was formulated that considered sign, transportation, and labor costs. As part of this effort, field measurements of retroreflectivity were made for more than 8,000 signs (with red, green, white, and yellow sheeting) in 28 counties in 26 States. Associated with this sample were data related to the agency having jurisdiction over the sign and the area type. The sign data indicated similar trends in the distribution of signs by retroreflectivity levels across State, county, city, and town classifications. The data also provided estimates of the distribution of signs by area and the number of signs, by type, per road mile (sign densities).

This research effort also included a large-scale survey of highway agencies regarding their sign management practices. The 1990 survey was distributed to over 900 State, county, and city highway agencies, with a 30 percent response rate. A review of the responses found that, at that time:

  • Approximately 33 percent of the States had sign inventories, as did many county and city agencies;
  • Over 90 percent of the inventory systems included information on sign type;
  • More than 75 percent of the inventories included installation or replacement date information;
  • More than 50 percent of the inventories had data on the sign sheeting material; and
  • Sign fabrication and maintenance costs were captured, and reasons for sign replacement were isolated.

The methodology used for the economic analysis involved expanding the sample for each of the jurisdictions based upon the area type, roadway mileage, and estimated sign densities. The percentage of signs at each retroreflectivity level was applied to the count by type, with those not meeting the criteria scheduled for replacement. All signs were degraded using algorithms from other FHWA research for the next analysis year. This process was repeated annually for the five alternative implementation periods. The replacement costs were summed for each type of agency to assess the impacts by type of agency.

The NCHRP study considered two sets of criteria for nighttime sign visibility (based on retroreflectivity) as shown in Table 5. The values for minimum maintained sign retroreflectivity levels that are currently proposed for inclusion in the MUTCD are also provided for the corresponding categories. The current proposed values are comparable, even though they span a broader range of materials than was considered in the NCHRP study.

Table 5. Comparison of Minimum Levels Used in NCHRP Analyses and Updated Minimum Levels
Sheeting Color NCHRP Report 346 — Lower Value NCHRP Report 346 — Upper Value Minimum Values Proposed for MUTCD
Red 8 21 7
Yellow 20 60 50/75
Green 8 10 15
White 35 70 50


NCHRP Report 346 concluded that, at the lower criteria and with a ten-year implementation schedule, the projected annual sign maintenance costs "were in the same range" as existing sign maintenance costs. Thus, the lower criteria should have relatively minor economic impacts on jurisdictions. The report went on to say, "this finding suggests that current sign maintenance standards are adequately maintaining signs above the lower standard." The report noted that the findings were based upon a sample of signs in the various jurisdictions, that overhead and street name signs were not included, and that averaged estimates of the various costs elements for sign maintenance were used. Thus, the impacts for any particular jurisdiction may vary. It was noted that sign inspection costs were estimated to be less than 5 percent of the annual sign maintenance budget. The report further noted the need for additional research on the deterioration of retroreflective properties, the development of field methods for evaluating sign retroreflectivity, and an analysis of the potential liability of agencies due to inadequate signing.

The findings of this study were limited to Type I and Type III sheeting materials which were the most widely used at the time. It can be inferred that since the newer microprismatic materials (i.e., Types VII, VIII, IX, and X) have higher costs (see Table 2) the resultant cost impacts on agencies would be higher. The results, however, indicate that the impacts on an agency should be small, if conducted over an extended implementation period.

4.2. FHWA Impact Analysis

The publication FHWA-RD-97-0536 summarized the findings of a survey of 19 State and local agencies relative to their sign management processes and the potential impacts of proposed minimum maintained traffic sign retroreflectivity levels outlined in Reference 12. The surveys distributed to these agencies solicited information on the types of sign materials used, the unit costs for materials, typical replacement costs, and perceived impacts of the new requirements. The survey results indicated that there were significant variations in sign upgrade needs and management costs. For example, the estimates for the percentage of signs needing replacement ranged from 1 to 61 percent based upon specific types of signs. The highest percentage related to the special needs of the red color used for STOP signs. The degree of sign maintenance performed by an agency was a factor, with some agencies facing higher costs to bring sign systems into compliance than others. Similarly, some agencies cited that there would be little or no impact on their sign management operations while others cited the need to hire new staff (one State agency estimated the need for 76 additional persons), purchase retroreflectometers and new vehicles, and conduct a large initial sign replacement effort.

Seven of the agencies contacted were able to provide retroreflectivity data for a sample of their signs. The retroreflectivity data was compared with the proposed minimum levels to determine the percentage of signs that would need to be replaced. Aggregate estimates of sign replacement costs were generated by applying equivalent percentages of replacement by highway type for the other parts of each of these seven jurisdictions. The data gathered for this analysis found only limited application of sign materials other than Types I, II, and III. Since microprismatic materials (i.e., Types VII, VIII, IX, and X) have higher costs, the degree of impact would be higher where these materials are substituted for previously used materials.

Table 6 presents the information in Table 10 from Reference 6. It was concluded from the analysis of the data gathered for sign conditions in 1994 that about 5 percent of the signs under State jurisdiction and 8 percent of the signs under local jurisdiction would not meet the proposed minimum requirements. Based upon the estimated sign replacement costs, the report calculated that bringing all signs in the U.S. into compliance would cost agencies $176 million, in 1994 dollars ($32 million for State agencies and $144 million for local agencies). The study did not analyze annual costs over varying implementation periods, but noted that replacement over a longer period of time would be the best approach. Furthermore, the report calculated the total cost of sign replacement, but did not itemize the marginal cost of upgrading the sign face material.

Table 6. Percentage of Signs Not Meeting Proposed Minimum Retroreflectivity Levels
Sign Group Sheeting Color State Jurisdiction Local Jurisdiction Combined
Group 1 Black Legend on Yellow or Orange Background 3.01% 9.51% 8.77%
Group 2 Black or Black-and-Red Legend on White Background 3.68% 6.86% 4.40%
Group 3 White Legend 1.67% 3.44% 2.11%
Group 3 Red Background 4.31% 7.81% 5.15%
Group 4 White Legend 3.77% 5.81% 4.13%
Group 4 Green Background 9.61% 2.90% 8.46%
All Signs Legend 2.31% 3.98% 2.69%
All Signs Background 4.48% 8.00% 5.48%


The impacts reported in the FHWA study are consistent with NCHRP Report 346. The estimate of 5 to 8 percent of signs requiring replacement is lower than the basic replacement rate that would be assumed if the agency had a 10-year replacement program (i.e., 10 percent of the signs would be replaced each year). Furthermore, an agency can accelerate the compliance process by upgrading the retroreflectivity of those signs needing replacement due to vandalism, knock downs, or changing traffic control schemes.

4.3. State Agency Impacts Analyses

4.3.1. Texas DOT

A study conducted by the Texas Transportation Institute14 compared the results of nighttime visual inspections with proposed minimum maintained sign retroreflectivity levels. In this effort, Texas DOT sign crews were asked to conduct inspections of 50 signs set up by the research team on a closed course in College Station, TX. The measured retroreflectivity value was known for each sign in this sample of regulatory, warning, and guide signs. More than 200 Texas DOT sign crew members participated in these inspections.

This study concluded that more signs were rated "unacceptable" in the visual inspections than would have been rejected by comparing the measured values with the proposed FHWA minimum sign retroreflectivity values. This is because observers consider factors that are not captured by using retroreflectometers. In this effort, the luminance uniformity of the sign face was a focus of attention. Other damage and the influence of the environment on sign visibility were also noted.

This study confirmed that there are often clearly obvious problems with the visibility of signs at night. It further confirmed that non-measurement approaches for assessing signs are effective and that a sign management system using visual nighttime inspections may result in a sign system that has higher minimum maintained sign retroreflectivity levels than are currently proposed.

4.3.2. Indiana DOT

The Indiana DOT contracted with Purdue University to help them determine the likely cost impacts of new FHWA regulations on their sign management program.15 At that time, the State only used Type III sign sheeting material, relied on manufacturer's warranties, and had a ten-year replacement cycle for their signs. The Purdue research team developed a sampling scheme to assess signs in different parts of the State and to measure the average retroreflectivity for each sign. They ultimately sampled 1,613 signs of various types between June 2001 and May 2002. Attribute information about each sign was also captured. The retroreflectivity measurements were compared to the minimum levels proposed in the FHWA's 1998 report that corresponded to the type and size of sign (Reference 12). Based upon the sample, it was concluded that:

  • Approximately 98 percent of the signs in the field should not only meet, but exceed, the proposed FHWA minimum retroreflectivity levels for any speed or any size of sign.
  • Sign retroreflectivity degrades over time at different rates based on the color of the sign. The red signs showed the quickest degradation in retroreflectivity.
  • There is no statistically significant difference in the retroreflectivity values for cleaned versus un-cleaned signs.
  • There was no statistically significant difference in sign retroreflectivity in districts where there is believed to be higher levels of environmental pollution.
  • There is limited effect of the sun on degradation related to the direction a sign faces.

The researchers recommended that the State alter its replacement policy to add two years to the replacement cycle for all signs, except STOP signs (i.e., use a 12-year replacement cycle).

The report concluded that there would be a negligible impact of the proposed minimum retroreflectivity levels, but cautioned that the conclusions were based upon a small sample. It is not clear to what extent the signs on local roads were considered. The study did demonstrate the value of monitoring sign retroreflectivity performance over time to get the fullest use of sign life.

4.3.3. North Carolina DOT

In 2000, the North Carolina DOT contracted with the North Carolina State University to investigate the impacts of the proposed minimum levels for traffic sign retroreflectivity.16 The researchers conducted numerous interviews, observed current sign management processes, and reviewed related literature from other agencies. They generated a long list of possible alternatives that the State could pursue and then evaluated the impacts of each. They estimated that North Carolina had over three million signs on their 78,000+ miles of streets and highways under State, county, and local jurisdiction.

The report documented in detail many aspects of sign management. For example, they conducted a rigorous review of sign inventory and management software packages. They reviewed the implications of decisions related to the selection of sign sheeting materials over a 50-year life cycle. In this analysis, the costs of upgrading the State's 51,000 STOP signs from Type I to high-intensity sheeting (Types III and IV) and from Type I to microprismatic sheeting (Types VII, VIII, IX, and X) were explored. They showed that due to the longer life of higher-end retroreflective materials, an agency can actually save money through fewer replacement cycles over time. This was shown to be true to a point, as the option of using microprismatic sheeting costs more than the option of using high-intensity sheeting over time.

The report included estimates of the number of signs in the State by color group and generated estimates of the number of signs in each group that would not meet the proposed minimum levels, based on the data in Reference 6 (see Table 6). Although there are an estimated 74,639 non-compliant signs, this represents less than 3% of the total number of signs in North Carolina. Assuming that the non-compliant signs are replaced during normal sign maintenance activities, over a seven-year implementation period there would likely be very little impact on the agency.

The report identified a wide range of approaches for agencies to follow to improve night visibility of traffic signs. The various elements were packaged into strategies and cost estimates for each strategy were developed. The report recommended that the State implement a comprehensive sign management system that would incorporate an inventory of all signs. Further, a tort tracking system was proposed to monitor any claims against the State associated with inadequate signs. Several million dollars in costs would be associated with these recommendations.

This report concluded that the proposed minimum maintained sign retroreflectivity levels would have a significant cost impact on the State. But, when components of the implementation are evaluated, it is noted that the impacts included not only the cost of sign replacements, but also establishment of a state-of-the-art GIS-based sign inventory and management system and a tort claims tracking system. Since these systems are not required to meet minimum retroreflectivity levels, they should not be considered as a direct impact of this rulemaking.

4.4. Tort Liability

The North Carolina report attempted to address the concern of tort liability, which has often been cited by agencies as a primary concern, through a review of the legal liability of the State and its local communities under the North Carolina Tort Claims Act. The report noted that, for the thousands of tort claims against the State annually, only 45 claims were issued against the North Carolina DOT from November 2000 to October 2001, of which only eight directly cited sign maintenance or sign management issues. Of these eight claims, six were dismissed for various reasons. The report cited the need for the agency to maintain a formal sign maintenance and inspection system to prevent lawsuits and provide a sound defense.

It is not possible from this limited analysis to make any inferences about whether the proposed minimum maintained retroreflectivity levels for traffic signs will lead to increased tort liability. Further, each State has different laws related to State liability and limitations to claims, which affect tort impacts.

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