Safety in Numbers and Safety in Congestion for Bicyclists and Motorists at Urban Intersections

Kristin Carlson, Alireza Ermagun, Brendan Murphy, Andrew Owen and David Levinson

No 165, Working Papers from University of Minnesota: Nexus Research Group

Abstract: This study assesses the estimated crashes per bicyclist and per vehicle as a function of bicyclist and vehicle traffic, and tests whether greater traffic reduces the per-car crash rate. We present a framework for comprehensive bicyclist risk assessment modeling, using estimated bicyclist flow per intersection, observed vehicle flow, and crash records. Using a two-part model of crashes, we reveal that both the annual average daily traffic and daily bicyclist traffic have a diminishing return to scale in crashes. This accentuates the positive role of safety in numbers. Increasing the number of vehicles and cyclists decelerates not only the probability of crashes, but the number of crashes as well. Measuring the elasticity of the variables, it is found that a 1% increase in the annual average daily motor vehicle traffic increases the probability of crashes by 0.14% and the number of crashes by 0.80%. However, a 1% increase in the average daily bicyclist traffic increases the probability of crashes by 0.09% and the number of crashes by 0.50%. The saturation point of the safety in numbers for bicyclists is notably less than for motor vehicles. Extracting the vertex point of the parabola functions examines that the number of crashes starts decreasing when daily vehicle and bicyclist traffic per intersection exceed 29,568 and 1,532, respectively.

Keywords: Safety; Bicyclist crashes; Returns to scale; Road intersection (search for similar items in EconPapers)
JEL-codes: R41 R48 (search for similar items in EconPapers)
Date: 2017
New Economics Papers: this item is included in nep-hea, nep-tre and nep-ure
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Published in Transportation Research Record. 2673(6) 677–684

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http://hdl.handle.net/11299/189809 First version, 2017 (application/pdf)

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Persistent link: https://EconPapers.repec.org/RePEc:nex:wpaper:safetyinnumbers-bikes

DOI: 10.1177/0361198119846480

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