Exploring Impacts of Factors Contributing to Injury Severity at Freeway Exit Ramps

Document Type

Conference Proceeding

Publication Date



injuries, ramps, traffic management

Digital Object Identifier (DOI)



Several factors of freeway mainlines, exit ramp sections, and cross-roads, such as geometric design, environment, vehicle/driver characteristics, and traffic features, may have significantly impacts on crash injury severity at freeway exit ramps. Freeway exit ramps are defined as the sections from the painted nose to the ramp terminal, and provide limit accesses from freeway mainlines to cross-roads. To explore the impacts and address the significant factors, injury severity prediction models was developed in this paper using three regression technologies: Ordered Probit, Partial Proportional Odds, and Heterogeneous Probit. The analysis results showed that ramp configuration (Diamond, Free-flow Loop, Outer Connection, and Parclo Loop) has significant impacts on crash injury severity at exit ramp sections. Diamond ramp is safer than other configurations while Outer Connection seems to increase crash injury severity than other ones. Other significant factors include lane configuration, channelization at ramp terminals, distance between ramp terminal and the first intersection on crossroads, speed limit on ramps and mainlines, shoulder width on ramps, and alcohol/drug involvement.

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Citation / Publisher Attribution

T&DI Congress 2011 : Integrated Transportation and Development for a Better Tomorrow, p. 1266-1285