DEVELOPMENT AND APPLICATION OF CRASH MODIFICATION FACTORS FOR TRAFFIC FLOW PARAMETERS ON URBAN FREEWAY SEGMENTS

Abstract

Attempts to apply more evidence-based methodologies to traffic safety have recently intensified. One such attempt is the Highway Safety Manual (HSM, 2010), which provides crash modification factors (CMFs) for a variety of roadway treatments. CMFs provide traffic practitioners with the resources to estimate the safety effects of various countermeasures. At the moment, the HSM does not provide CMFs for traffic flow parameters despite the significant differences in the number of crashes on segments with similar geometric parameters and average annual daily traffic (AADT). This study develops CMFs associated with change in hourly traffic flow conditions for 2008 through 2011 on three similar urban freeway segments in New Jersey using Empirical Bayes (EB) for before-after road safety studies. Specifically, this study focuses on traffic density expressed as level of service (LOS). Results show significantly that, as the LOS deteriorates from A to B, B to C, C to D, and D to E, the resultant CMFs are 0.673, 1.11, 0.865, and 1.452 respectively. This demonstrates that traffic flow parameters have some significant effect on roadway safety, therefore needs to be investigated further and eventually included in the future editions of the HSM.