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Crash Rates

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Traffic Engineering

Introduction

Crash rates can be an effective tool to measure the relative safety at a particular location. The combination of crash frequency (crashes per year) and vehicle exposure (traffic volumes or miles traveled) results in a crash rate. Crash rates are expressed as "crashes per Million Entering Vehicles" (MEV) for intersection locations and as "crashes per Million Vehicle Miles Traveled" (MVMT) for roadway segments.

Crash Rate Analysis

This crash rate analysis method can be a useful "first brush" tool when determining how a roadway location compares to the average of those contained in the database. If, during a traffic study, a subject location is found to have a higher than average crash rate, the engineer should perform a detailed review of the crash records (through the State and local police departments) to determine key crash factors and attempt to develop countermeasures to reduce the incidence of crashes.

Crash Rate Summary

The Crash Rate Summary provides the most current average crash rates available for use in Massachusetts. Summary crash rates for a given year actually reflect an accumulation of crash rate data for a number of preceding years, not just for the crash rate year that is indicated. Furthermore, data included do not represent a random sample of locations for the specified intersection type or road segment functional classification or roadway type, so these data should be used with some caution and only as a general screening tool. The MassDOT Crash Rate Worksheets for Intersections and Segments are available, and the procedures for calculating crash rates are noted below. Crash data necessary to produce crash rate calculations is available from the MassDOT Safety Management Unit by contacting us via the MassDOT Crash Portal or via email: crashdatarequest@state.ma.us.

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