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. In 2008, South Carolina tackled the problem on a mile of US 25 in Greenville County that was curvy and prone to rain. According to a Federal Highway Administration case study, the state treated the road with grippy surfacing.

Wet crashes were down by 68%, and total crashes fell 56%. The entire job cost $1 million. Why this one mile worried engineersThe stretch was in rural, mountainous country, and the case study says it often experienced rain, snow, ice, and fog. 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.

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. Why the big rebuild never happenedThe state considered a full reconstruction in 2000. The plan would have involved removing the barrier wall and changes to the road’s banking and drainage. But the estimate was close to $5 million, and the project would take about three years. It would have also meant a big construction zone and detours for local drivers. The cheaper steps came first.

Crews added extra signage and markings, and at one point a message sign showed a 45 mph limit in the rain. But the report says the measures achieved little, and speeds were still too high on the wide rural road. How the grippy surface worksThen 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 treatment improves skid resistance, particularly around curves in wet weather. South Carolina has used the treatment on ramps in the past. 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 planning and installation took about six months. The $1 million price tag was about 80% less than the rebuild plan. What the numbers showedA before-and-after study showed substantial improvements.

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. The state said the surface was holding up well even after six years of snow plowing. The state transportation department also referenced a before-and-after study of seven treated sites. 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. What wider research saysOne 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. 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 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. The lesson of US 25 is simple. 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.