Safety Evaluation of Wet-Reflective Pavement Markings

Executive Summary

The Federal Highway Administration (FHWA) established the Development of Crash Modification Factors (DCMF) program in 2012 to address highway safety research needs for evaluating new and innovative safety strategies (improvements) by developing reliable quantitative estimates of their effectiveness in reducing crashes. The ultimate goal of the DCMF program is to save lives by identifying new safety strategies that effectively reduce crashes and to promote those strategies for nationwide implementation by providing measures of their safety effectiveness and benefit–cost (B/C) ratios through research. State transportation departments and other transportation agencies need to have objective measures for safety effectiveness and B/C ratios before investing in new strategies for statewide safety improvements. Thirty-eight State transportation departments provide technical feedback on safety improvements to the DCMF program and implement new safety improvements to facilitate evaluations. These States are members of the Evaluation of Low-Cost Safety Improvements Pooled Fund Study (ELCSI-PFS), which functions under the DCMF program.

One of the strategies selected for evaluation for this study was the application of wet-reflective pavement markings. This strategy involves upgrading existing markings from standard marking materials to wet-reflective markings applied as a paint, tape, or thermoplastic material. These markings are designed to provide an improved level of retroreflectivity during wet-road surface conditions. A literature review found that although there was some cross-sectional research relating retroreflectivity levels to crashes, there was no published research evaluating the effect on crashes after applying wet-reflective markings.

Geometric, traffic, and crash data were obtained for treated freeway sections in Minnesota, North Carolina, and Wisconsin; treated two-lane rural road locations in Minnesota; and treated multilane road sections in Wisconsin. To account for potential selection bias owing to regression-to-the-mean, an Empirical Bayes (EB) before–after analysis was conducted using reference groups of untreated road sections with similar characteristics to the treated sites. The analysis also controlled for changes in traffic volumes over time and time trends in crash counts unrelated to the treatment. The evaluation was done for the following crash types: total, injury, side-swipe same direction, run-off-road, wet-road, wet-road nighttime crashes, and all nighttime crashes. None of these crash types considered intersection-related, snow/slush ice snow/slush/ice*, or animal crashes.

For freeways, the combined results for all States indicated reductions in crashes that were statistically significant at the 95-percent confidence level for injury and wet-road crashes, with estimated crash modification factors (CMFs) of 0.881 and 0.861, respectively. For multilane roads, statistically significant reductions were estimated for total crashes (CMF = 0.825), injury crashes (CMF = 0.595), run-off-road crashes (CMF = 0.538), wet-road crashes (CMF = 0.751), and nighttime crashes (CMF = 0.696). For two-lane roads, the sample of crashes was too small to detect an effect with statistical significance for any of the crash types, but there were indications that the treatment had a safety benefit for wet-road crashesand overall*.

B/C ratios estimated with conservative cost and service life assumptions were 1.45 for freeways and 5.44 for multilane roads. With the U.S. Department of Transportation (USDOT) recommended sensitivity analysis, these values could range from 0.83 to 2.04 for freeways and 3.10 to 7.67 for multilane roads.⁽¹⁾ These results suggest that the treatment—even when making conservative assumptions on cost, service life, and value of a statistical life—can be cost effective, especially for multilane roads.

* Revised 3/12/2019