Road Traffic Congestion and Crash Severity: Econometric Analysis Using Ordered Response Models
Publication: Journal of Transportation Engineering
Volume 136, Issue 5
Abstract
There is an ongoing debate among transport planners and safety policy makers as to whether there is any association between the level of traffic congestion and road safety. One can expect that the increased level of traffic congestion aids road safety and this is because average traffic speed is relatively low in a congested condition relative to an uncongested condition, which may result in less severe crashes. The relationship between congestion and safety may not be so straightforward, however, as there are a number of other factors such as traffic flow, driver characteristics, road geometry, and vehicle design affecting crash severity. Previous studies have employed count data models (either Poisson or negative binomials and their extensions) while developing a relationship between the frequency of traffic crashes and traffic flow or density (as a proxy for traffic congestion). The use of aggregated crash counts at a road segment level or at an area level with the proxy for congestion may obscure the actual relationship. The objective of this study is to explore the relationship between the severity of road crashes and the level of traffic congestion using disaggregated crash records and a measure of traffic congestion while controlling for other contributory factors. Ordered response models such as ordered logit models, heterogeneous choice models, and generalized ordered logit (partially constrained) models suitable for both ordinal dependent variables and disaggregate crash data are used. Data on crashes, traffic characteristics (e.g., congestion, flow, and speed), and road geometry (e.g., curvature and gradient) were collected from the M25 London orbital motorway between 2003 and 2006. Our results suggest that the level of traffic congestion does not affect the severity of road crashes on the M25 motorway. The impact of traffic flow on the severity of crashes, however, shows an interesting result. All other factors included in the models also provide results consistent with existing studies.
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Acknowledgments
The writers would like to thank the U.K. Highways Agency for providing traffic characteristics data for the M25 motorway. The content of the paper, however, does not express the views of the Highways Agency and the writers take full responsibility for the content of the paper and any errors or omissions.
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Information & Authors
Information
Published In
Journal of Transportation Engineering
Volume 136 • Issue 5 • May 2010
Pages: 424 - 435
Copyright
© 2010 ASCE.
History
Received: Mar 3, 2009
Accepted: Dec 22, 2009
Published online: Dec 28, 2009
Published in print: May 2010
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