In North Carolina, a wet pavement detection system on I-85 yielded a 39 percent reduction in the annual crash rate under wet conditions.
Made Public Date


Mecklenburg County
North Carolina
United States

Traffic Safety Effects of a Wet Pavement Detection System Installed on a North Carolina Interstate: A Statistical Summary of Crash Data for a Temporary On-Site Detour inside an I-485 Construction Zone in Mecklenburg County

Summary Information

In June 2002, the North Carolina DOT (NCDOT) opened a three-quarter mile temporary traffic detour around an I-85 bridge construction project in Mecklenburg County. When the detour was opened there were large sections of standing water on the roadway during heavy rains. The standing water was a factor in several hydroplane crashes. The NCDOT decided to install a wet pavement detection system (WPDS) in March, 2003 to help alleviate some of the impacts of the temporary hazardous situation. This report summarized the traffic safety effects on this section of roadway and quantified the differences in crash experience due to deployment of the WPDS.

Analyses performed included a before and after study as well as a comparison study along a similar stretch of nearby interstate. Crash data was obtained from the NCDOT's Traffic Engineering Accident Analysis System database and volume data was obtained from the 2002 NCDOT Average Annual Daily Traffic (AADT) maps. The before data was collected for 270 days and the after data collected for 217 days. The data was then converted to yearly crash rates for comparison purposes. The NCDOT also chose a section of I-85 in Gaston County that experienced among other factors, similar weather conditions, traffic volumes, and vehicle fleet to use for the comparison analysis.

  • The WPDS reduced the yearly wet crash rate by 39 percent.
  • The WPDS reduced the yearly injury crash rate by 35 percent.
  • The average daily crashes per day dropped by 58 percent on days defined as having heavy precipitation.
Based on the results of the studies performed, the WPDS was effective in preventing crashes at the temporary traffic detour during periods of heavy precipitation when compared to a similar location.