A 2020 Federal Highway Administration (FHWA) study examined what happened when transportation agencies addressed that problem with high-friction surface treatment (HFST). A road surface can look ordinary to drivers, but its grip on tires can change when rain begins. On sharp curves, that loss of grip can increase the risk of a roadway-departure crash.
A research paper published in Transportation Research Record reached a similar conclusion, finding substantial and statistically significant safety benefits for HFST at curves, particularly for wet-road and roadway-departure crashes. The researchers also found that the treatment’s effectiveness was related to the amount of friction improvement, traffic volume, and the number of crashes expected before treatment. In addition, researchers looked at whether HFST could preserve its friction performance after installation. The study found that HFST significantly improved friction and maintained high friction levels even under heavy traffic over time. This ability to sustain high friction values is crucial since HFST is applied only in specific locations. More recent research has also examined the treatment.
Across the three states, the treated sites had an average annual traffic volume of roughly 6,000 to 8,000 vehicles, depending on the state. The crash modification factor for wet-road crashes was 0.168, meaning the post-treatment crash rate was about 16.8% of the expected level without treatment. That corresponds to an approximately 83% reduction . In another FHWA study conducted concurrently, friction was measured both prior to and following the application of the HFST at 99 sites in Georgia and Pennsylvania. A 2024 study in Accident Analysis & Prevention analyzed HFST on horizontal curves in Pennsylvania using propensity-score matching combined with an empirical Bayes before-and-after approach.
Because it used an empirical Bayes before-and-after methodology, a statistical approach intended to account for factors such as regression to the mean and changes in traffic conditions, the 2020 FHWA study was especially significant.
It found statistically significant reductions across the crash types and severities examined, adding further evidence to the earlier FHWA findings.
Still, the 83% figure should not be treated as a guarantee that every treated curve will see the same reduction. Crash rates depend on several factors, including traffic levels, weather, driver behavior, and roadway type. However, the FHWA research itself showed that the level of safety gain was site-specific. Rather than rebuilding every dangerous site, highway authorities can use HFST where extra tire grip is most critical.
