In 2008, South Carolina tackled the problem on a mile of US 25 in Greenville County that was curvy and prone to rain. Wet crashes were down by 68%, and total crashes fell 56%. The entire job cost $1 million.
The state treated the road with grippy surfacing, according to a Federal Highway Administration case study . Most of us have felt that tiny slip when a car brakes on a wet road. On a curve, that slip can quickly become dangerous.
It carried about 10,000 vehicles a day, many of them being heavy trucks. The speed limit was 55 mph. The road had curves and a 6% grade, and the two directions were separated by a broken concrete barrier. Then came 2008, when workers applied a high-friction surface treatment to the winding stretch. In a 2021 TechBrief, High Friction Surface Treatments , FHWA explains that the method attaches calcined bauxite, a polish-resistant material, to the pavement with a polymer-resin binder. The $1 million price tag was about 80% less than the rebuild plan. Wet crashes were down 68%, and total crashes were down 56%. A chart on the FHWA page shows wet crashes going from 8.1 a year down to 2.6, and total crashes from 9.6 a year to 4.2. It found 71% fewer total crashes and 81% fewer wet crashes. By 2015, the state had installed 20 such projects and planned about 20 more that year.
The stretch was in rural, mountainous country, and the case study says it often experienced rain, snow, ice, and fog. But this was its largest use to date, and the case study says it was not known at the time whether it would solve the water problems. The state said the surface was holding up well even after six years of snow plowing.
Engineers also found that the barrier design did not allow water to drain properly. Instead, it dumped water onto the roadway and shoulder. Speeding, curves that were not banked enough, and limited sight distance made things worse. The treatment improves skid resistance, particularly around curves in wet weather. South Carolina has used the treatment on ramps in the past. The planning and installation took about six months. A before-and-after study showed substantial improvements. The state transportation department also referenced a before-and-after study of seven treated sites.
It found a 57% reduction in expected crashes on curves and an 83% reduction in wet-weather crashes. The study also estimated savings of about $19.3 million across 146 curve installations. The lesson of US 25 is simple.
One road might not tell the whole story. But wider research backs the same conclusion. The same TechBrief describes a study that used crash, friction, and pavement data from four states. The brief notes that results can vary widely, leaving agencies guessing what to expect. It still calls the treatment a cost-beneficial investment, particularly in areas with a high frequency of wet-weather crashes. A targeted fix on a short trouble spot can help. It took about six months to do the job here, whereas a rebuild would have taken about three years.
