Traffic Flow Conditions Associated with Truck-Involved Crashes on the Freeway

Large turning radian and heavy weights make the truck a special traffic component. Because of its unique character, a truck is more likely to be involved in a traffic crash. Traffic flow conditions before a crash occurrence have been studied by several researchers in this field. However, the crash is always considered as an entirety which does not care about the type. This paper focuses on investigating and comparing different traffic states associated with truck-involved crashes on the freeway. Matched case-control is used to conduct the data collection. K-means is selected to do the traffic states classification and a conditional logistic regression model is adopted to compare the different traffic states associated with truck-involved crash risk. The findings tell that the free-flow condition, both upstream and downstream, is the most secured traffic state and is consistent with former conclusions when the crash was considered as an entirety. However, for a truck-involved crash, the most dangerous state is no longer the one with free upstream and congested downstream, but rather both congested flows upstream and downstream. The results of this study fill up the research gap in this field and lead the work into more detailed scale.