Impact of Pavement Friction on Traffic Safety, Phase 1: Pavement Friction Evaluation

Project Details



19-719, 20-SPR0-008








Iowa Department of Transportation

Principal Investigator
Omar Smadi

Director, CTRE

About the research

Safety performance is a crucial component of the highway network performance evaluation. Due to the complexity of a traffic crash event, it is a challenging task to identify all the contributing factors affecting a crash, and even more challenging to quantify their level of impact on crash rates. Several studies have pointed to a strong correlation between pavement skid resistance and crash rates. However, these correlations are in most cases state specific or even site specific. This variation and the lack in understanding the impact of pavement skid resistance on traffic safety, makes it hard to specify the segments with high crash risk due to lack of skid resistance and to propose cost effective friction remedies. The act of measuring pavement friction, identifying roadway locations with high crash rates related to low skid resistance, and proposing effective friction treatments are all components of a pavement friction management (PFM) program.

In an initial effort, the team at Iowa State University studied the impact pavement skid resistance has on roadway departure crashes under different weather conditions. Based on the limited records available, it was found that road segments with lower skid numbers had higher roadway departure crash risk for both wet and dry crashes. Based on the initial investigations and the literature review performed by the ISU team, following are some of the identified research needs:

  1. Better understanding of the impact of pavement friction on the crash risk given the friction demand required for a safe travel, which is function of the weather condition, roadway geometry, traffic condition, and other safety treatments.
  2. Modify the procedure for deriving generalized skid resistance thresholds based on friction demand, by considering a more dynamic approach that focuses on crash probability distributions for a given pavement skid resistance and the unique road segment characteristics.
  3. Understand and quantify the possible benefits of friction treatments, such as the high friction surface treatment, given the current road segment characteristics.
  4. Define a consistent and improved selection criteria for friction treatments.
  5. Identify the proper tools to measure and summarize pavement friction on tangents and curves.

In the proposed project, a thorough analysis will be conducted to help understanding and quantifying the impact of pavement friction on crash risk under various weather and traffic conditions. This will be achieved by integrating the crash records with the skid measurements provided in the Iowa Pavement Management Information System and acquired during the project, segment characteristics and geometry, and weather records on critical curves and segments.