*Although the crash rate methodology is being replaced with a more scientific approach to safety, it is described here using the current standards until the newer methodology is completed.
Crash rates — crashes per year, measured against vehicle exposure (traffic volumes or vehicle miles traveled) — are an effective "first brush" tool for roadway safety design. The engineer can use crash location-specific records — along with MassDOT's crash rate worksheets and calculation procedures — to determine crash rates for an intersection or road segment.
We express crash rates as:
- crashes per Million Entering Vehicles (MEV) for intersection locations
- crashes per Million Vehicle Miles Traveled (MVMT) for roadway segments
Summary crash rate data provides the most current average crash rates for roadways, road segments, and intersections. With regard to intersections, data for a given year will also contain data from some preceding years. The data is not a random sample of locations for intersection type, so use it with caution, or only as a general screening tool.
Intersection Crash Rates
The intersection average crash rates are based upon a database of signalized and unsignalized intersection crash rates that are compiled by MassDOT. The database contains intersection crash rates, obtained from crash rate worksheets that have been submitted to MassDOT as part of the review process for an Environmental Impact Report or Functional Design Report. MassDOT enters the information directly from the crash rate worksheet into the database. The statewide average crash rates merely reflect the average of those rates contained in the database and the district-wide crash rates reflect the average of those crash rates in the particular district, calculated for both signalized and unsignalized locations. The most recent average crash rates, which are updated on a nearly yearly basis, are based on all entries in the database not just those entries made within the past year.
|Location||Signalized Intersections||Unsignalized Intersections|
* - District 1 should use Statewide Rates due to low sample total
Crash Rates by Roadway Functional Classification
The statewide average crash rates by roadway functional classification are based upon the total number of located crashes and the vehicle miles traveled for each roadway functional classification. All crashes contained in the statewide crash system that were able to be located to a geographic point, were linked to the roadway network and to a corresponding roadway functional classification (for crashes along a roadway that occurred at an intersection, the higher functional classification was assumed). The sum of all crashes for each functional classification was then calculated. The exposure, in this case, the million vehicle miles traveled (MVMT) by functional system, was obtained from MassDOT Planning as part of their HPMS reporting. For each functional classification, the total number of crashes was then divided by the MVMT.
In 2017, approximately 96% of all crashes were able to be geographically located to a point. However, it should be noted that the rate for which crashes are able to be located is not uniform for each roadway, thereby impacting the crash rate on a particular roadway and subsequently on the average crash rate by functional classification.
|Roadway Federal Functional Classification||Rural||Urban|
|Principal Arterial – other freeways and expressways||0.67||0.80|
|Principal Arterial – other||0.57||3.58|
Notes on Functional Classification Data:
- * This rate is for all Urban Collector roads, including both Urban Major Collector and Urban Minor Collector roadways.
- If a crash occurred at an intersection or along two different functional classifications, the crash was assigned to the higher order roadway.