CTRE is an Iowa State University center, administered by the Institute for Transportation.

Address: 2711 S. Loop Drive, Suite 4700, Ames, IA 50010-8664

Phone: 515-294-8103
FAX: 515-294-0467

Website: www.ctre.iastate.edu/

Iowa State University--Becoming the Best

Crash Location Correction for Freeway Interchange Modeling


Principal investigator:

Co-principal investigators:

Project status


Start date: 07/21/14
End date: 09/30/16


Report: Crash Location Correction for Freeway Interchange Modeling (2.54 mb pdf) January 2017



About the research


The American Association of State Highway Transportation Officials (AASHTO) released a supplement to the Highway Safety Manual (HSM) in 2014 that included models for freeway interchanges composed of segments, speed-change lanes, and terminals. A necessary component when using the HSM is having the appropriate safety-related data. However, a high percentage, approximately 75 percent, of interchange crashes in the Missouri Department of Transportation (MoDOT) Transportation Management System (TMS) are landed on an incorrect location within an interchange. For example, crashes are frequently assigned to the midpoint of the ramp terminal instead of to one of the two ramp terminals. Another example includes crashes that are assigned to the freeway mainline when the crashes are related to the ramps. In order to properly calibrate and use HSM freeway interchange models, the location of crashes needs to be corrected. Crash landing correction involves the visual inspection of crash images compiled by the Missouri State Highway Patrol. A detailed procedure was established along with a reviewer test so that crash correction can be conducted uniformly among multiple reviewers. A total of 10,897 crashes were reviewed and 9,168 underwent detailed review and correction. Among the total crashes reviewed, 1,482 were partial cloverleaf crashes, 5,086 diamond interchange crashes, 780 ramp crashes, and 1,820 speed-change lane crashes. The crash location correction process helped to eliminate the error rate associated with interchange crash locations by 69 percent. Any analyst can correct crash locations by following the procedure detailed in the final report for this project.