The Effect of Road Environment Factors on Freeway Traffic Crash Frequency during Daylight, Twilight, and Night Conditions

Abstract

This research investigated the effect of road environment factors on freeway traffic crashes in Korea during the years 2007 through 2010 under the light conditions: daylight, twilight, night, and for comparison the whole 24 hour day. Both random and fixed parameter crash frequency models were estimated and applied in the analysis. Several factors had statistically significant effects only during certain light conditions, notably, number of interchanges/junctions and number of bridges during daylight; traffic share of heavy vehicles during night and the whole 24 hour period; short tangent (<1,421 m) and number of crest vertical curves during twilight. Several factors were statistically significant regardless of light conditions, notably, traffic share of light vehicles, number of lanes, urban area, frequent fog in area, and number of days with snowfall. The random parameter model structure was found to be important because several factors had random effects: traffic share of light vehicles, number of lanes, urban area, and foggy area. Foggy areas were associated with increased crash frequencies in about 75% of sections and reduced crash frequencies in about 25%. The results indicate that roadway design should avoid combining horizontal and sag vertical curves due to higher crash frequency. The varying effect of road environment factors on crash frequency by light condition should be used to improve driver information systems, for example, during daylight drivers need more information about pcoming interchanges/junctions.