Turner-Fairbank Highway Research Center

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Modeling the Probability of Freeway Rear-End Crash Occurrence

Product Type

Journal Article


Kim, J.K., Y. Wang, and G.F. Ulfarsson



Full citation

Kim, J.K., Y. Wang, and G.F. Ulfarsson. Modeling the Probability of Freeway Rear-End Crash Occurrence. In Journal of Transportation Engineering, Vol 133, No. 1, American Society for Civil Engineers, Reston, V.A., Jan 2007, pp. 11-19.


A microscopic model of freeway rear-end crash risk is developed based on a modified negative binomial regression and estimated using Washington State data. Compared with most existing models, this model has two major advantages: (1) It directly considers a driver's response time distribution; and (2) it applies a new dual-impact structure accounting for the probability of both a vehicle becoming an obstacle (Po) and the following vehicle's reaction failure (Pf). The results show for example that truck percentage-mile-per-lane has a dual impact, it increases Po and decreases Pf, yielding a net decrease in rear-end crash probabilities. Urban area, curvature, off-ramp and merge, shoulder width, and merge section are factors found to increase rear-end crash probabilities. Daily vehicle miles traveled (VMT) per lane has a dual impact; it decreases Po and increases Pf, yielding a net increase, indicating for example that focusing VMT related safety improvement efforts on reducing drivers' failure to avoid crashes, such as crash-avoidance systems, is of key importance. Understanding such dual impacts is important for selecting and evaluating safety improvement plans for freeways.

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Link To Journal Article

Modeling the Probability of Freeway Rear-End Crash Occurrence


Accident risk forecasting
Geometric segments
Highway factors in accidents
Lane distribution
Traffic flow
Reaction time
Rear end collisions
Regression analysis
Traffic models
Vehicle miles of

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