Safety in Numbers for Bicyclists at Urban Intersections

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

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


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-vehicle crash rate, a phenomenon referred to as “safety in numbers” (SIN). We present a framework for comprehensive bicyclist risk assessment modeling, using estimated bicyclist flow per intersection, observed vehicle flow, and crash records. Testing a two-part model of crashes, we reveal that both the average of annual average daily traffic (AADT) over a 14-year period and the estimated daily bicyclist traffic (DBT) have a diminishing return to scale in crashes. This accentuates the positive role of SIN. Higher volumes of vehicles and cyclists lowers 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 average of AADT across the time window increases the probability of crashes by 0.14% and the number of crashes by 0.80%. However, a 1% increase in the estimated DBT increases the probability of crashes by 0.09% and the number of crashes by 0.50%.

Original languageEnglish (US)
Pages (from-to)677-684
Number of pages8
JournalTransportation Research Record
Issue number6
StatePublished - Jun 1 2019

Bibliographical note

Publisher Copyright:
© National Academy of Sciences: Transportation Research Board 2019.


Dive into the research topics of 'Safety in Numbers for Bicyclists at Urban Intersections'. Together they form a unique fingerprint.

Cite this