United States Department of Transportation
i
Safety performance functions for ramp terminals at diamond interchanges.
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2011-07-01
[PDF-2.14 MB]
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Abstract:This report documents two efforts to support CDOT in the area of Safety Performance Function (SPF)
development. The first involved the data collection and development of SPFs for five categories of ramp
terminals at diamond interchanges. For each category, data for the period 2000 to 2006 were collected at sites
selected to ensure statewide geographical representation and coverage of the range of traffic volume and other
variables in each category. The second effort involved estimating the overdispersion parameters for a number
of existing SPFs already in use by CDOT for various roadway segment categories. These parameters are
required for implementing the state-of-the-art empirical Bayes procedure for various safety management
processes. The development of SPFs for the five categories of ramp terminals was successful. Separate SPFs
were developed for total and for injury (fatal+injury) accidents. The calibration of overdispersion parameters
for the existing roadway segment SPFs was also successful.
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