Urban freeway crash analysis - Geometric, operational, and weather effects on crash number and severity

Associations between the number of crashes and the severity of crashes with a long list of potentially contributing factors, such as geometric and operational characteristics and weather conditions, were investigated. Both aggregate and disaggregate databases with, crash statistics were used. Severity was estimated with constants for the different impact (cost) of fatalities, injuries, and material damages. Noteworthy associations included the negative correlation with the speed limit (spots with lower speed limits have more, or more severe, crashes), existence of merge-diverge pavement markings (suggesting the possibility of an illegal driving maneuver), downhill grade sections, and curves. Several temporal variables such as months, days, or time of day with a higher frequency of crashes worked well in models, but those were findings of local interest. An important outcome of this analysis is the absence of any major correlation, which implies that crashes on the modern and mildly congested Attica Tollway in Greece are events largely attributable to driver behavior and other circumstances that cannot be accounted for by geometric, operational, or other temporal variables. Findings of this research suggest that fixed and temporal roadway characteristics and the presence of rain or wet pavements may explain (and likely contribute to) about 5% to 10% of the crashes and severity of crashes observed in 2004 and 2005 on the Attica Tollway. The 2006 report from the 100-Car Naturalistic Driving Study concluded that nearly 80% of all crashes involved driver inattention, lending support to the finding that roadway and environmental factors are relatively minor causes of crashes.