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

摘要

This research investigated the effect of road environment factors on freeway trafficcrashes 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 andfixed parameter crash frequency models were estimated and applied in the analysis.Several factors had statistically significant effects only during certain lightconditions, notably, number of interchanges/junctions and number of bridges duringdaylight; 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. Severalfactors were statistically significant regardless of light conditions, notably, trafficshare of light vehicles, number of lanes, urban area, frequent fog in area, and numberof days with snowfall. The random parameter model structure was found to beimportant because several factors had random effects: traffic share of light vehicles,number of lanes, urban area, and foggy area. Foggy areas were associated withincreased crash frequencies in about 75% of sections and reduced crash frequencies inabout 25%.The results indicate that roadway design should avoid combining horizontaland sag vertical curves due to higher crash frequency. The varying effect of roadenvironment factors on crash frequency by light condition should be used to improvedriver information systems, for example, during daylight drivers need moreinformation about upcoming interchanges/junctions.