Turner-Fairbank Highway Research Center

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NCHRP Research Report 888: Development of Roundabout Crash Prediction Models and Methods

Product Type

Research Report


Erin Ferguson, James Bonneson, Lee Rodegerdts, Nick Foster, Bhagwant Persaud, Craig Lyon, and Danica Rhoades




Safety performance factors (SPFs) and crash modification factors (CMFs) are predictive models that estimate expected crash frequencies. Transportation professionals use these models to identify locations where crash rates are higher than expected, to estimate safety benefits of a proposed project, and to compare the safety benefits of design alternatives. The models help identify and prioritize locations for safety improvements, compare project alternatives by their expected safety benefits, and guide detailed design decisions to optimize safety. Research indicates that roundabouts provide substantial reductions in crashes, especially crashes that result in serious injuries or fatalities. However, the first edition of the HSM did not include a crash prediction method for roundabouts; therefore, practitioners were not able to quantitatively assess the crash reduction benefits of providing a roundabout at a specific intersection or to investigate the safety effects of complex design decisions at single lane and multilane roundabouts. This report provides practitioners with SPFs and CMFs for roundabouts. The models include variables for geometric features and operational characteristics, as well as their expected effects on crash rates for motorized and nonmotorized users. The models can be used for planning-level analysis, and, as a project develops and more detailed information is available, for analysis at the intersection level and leg level of an intersection.

Link To Research Report

NCHRP Research Report 888: Development of Roundabout Crash Prediction Models and Methods


Crash modification factors
Crash rates
Crash risk forecasting
Geometric segments
Highway safety
Mathematical prediction

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