Exploring the relationships between crash rates and average speed difference between cars and large vehicles on a suburban freeway

Freeway should be, and has been the safest highway comparing to other types of roadways due to its highest design standard. Whereas these years Chinese government was forced to pay more attention to freeway safety problems due to its leading fatality rates regardless of its luxury infrastructure criteria. Research on crash rates and speed has been achieved by many people, but paper about the relationship between crash rates and average speed difference between cars and large vehicles on freeway kept rare. This research explored this relationship using three-year crash data and traffic flow data of Beijing suburban section of one freeway. From the result it can be concluded that speed difference and crash rates are correlative, and similar empirical functions were obtained using compound, growth, and exponential curve to fit. The general law extracted from this paper showed: with the increasing of the average speed difference, the crash rates increased rapidly