[NTC2016-SU-R-02] Effect of Pavement Condition on Accident Rate

Accident statistics developed by the U.S. DOT as well as state and local DOTs show a large number of accidents that have notable implications on the economy (1, 2). Several factors affect the accident rate such as human factors, vehicular causes, environment, roadway geometry, pavement condition, and their combinations.

Pavement distresses directly affect ride quality, and indirectly contribute to driver distraction, vehicle operation, and accidents. For example, a pavement with a bad record of roughness or potholes can cause a vehicle to lose control when braking or turning, especially under adverse environmental conditions. When pavement roughness increases, the contact area between vehicle tire and pavement decreases, resulting in lower brake friction. Also, roughness can contribute to greater vehicle instability since different friction forces exist on the two sides of the vehicle. Another type of pavement distress that affects the accident rate is rutting. Rutting acts along a wheel path, and may result in a driver needing to exert extra effort to get out from the wheel path (if the rut depth is large), thus leading to uncertain and in some cases uncontrolled lateral vehicle movement. Moreover, rutting is more hazardous in wet weather when water accumulates in the rut path and leads to hydroplaning and loss of control. The problem can be further exaggerated when human factors, such as distraction, alcohol, stress and age, are combined with pavement distresses.

Transportation agencies try to improve roadway safety through proper pavement engineering and maintenance. This is a major transportation policy the agency needs to adopt in order to improve its economic competitiveness. The majority of the studies on the effect of pavement condition on safety were related to skid resistance, and not roughness or riding quality (e.g., 3, 4). There are limited studies that focus on exploring the relationship between accident frequency and pavement condition such as roughness and rutting (5, 6). These studies showed that increasing road roughness, in general, increases the rate of accidents. Very limited information is available to determine the pavement condition level the agency needs to maintain in order to actively reduce accident risk. Transportation agencies have been looking for the appropriate roughness and rut depth thresholds before which the ride quality should be improved for safety. Decision makers need to know the cost-effectiveness of maintenance in reducing the rate of accidents, especially in accident prone areas. Research is badly needed to develop models to predict accident rates as related to pavement condition so that transportation agencies can develop appropriate pavement management strategies that reduce the frequency of pavement-related accidents.