01657966

Component

Crash modification factors (CMFs) are one tool to estimate the expected safety effects of a given treatment. One practical limitation is that treatments may be considered in combination, but most CMFs represent the effect of a single treatment. Ideally, the analyst would use a CMF for the combination treatment of interest, but relatively few CMFs have been developed for combination treatments, and it would take a tremendous effort to develop CMFs for all likely combinations of treatments.Combining individual CMFs is one alternative to developing CMFs for every possible treatment combination, but there is limited guidance on the application of multiple CMFs. The predictive method from the first edition of the Highway Safety Manual shows that CMFs can be multiplied to estimate the combined effect of multiple treatments, assuming the treatments are independent. It further notes that limited research exists regarding the independence assumption. Further research and guidance is needed to help practitioners estimate the expected safety effects when multiple treatments are considered at the same location.This paper presents several potential methods for combining multiple CMFs and the associated strengths and limitations. A methodology is developed and then applied to test the accuracy of these methods. The method hinges on the development of high-quality CMFs for the two individual treatments in question as well as the CMF for the combined treatment. CMFs were developed and presented in a companion paper. The results of the methods assessment provide a solid foundation for recommending methods for combining multiple CMFs.

This paper was sponsored by TRB committee ANB25 Standing Committee on Highway Safety Performance.

18-00981

English

7p

2018

Transportation Research Board 97th Annual Meeting

Digital/other

References; Tables

Crash modification factors; Evaluation and assessment; Highway safety; Methodology; Traffic crashes

Highway Safety Manual

Treatment (Safety)

Highways; Planning and Forecasting; Safety and Human Factors

Transportation Research Board Annual Meeting 2018 Paper #18-00981

TRIS, TRB, ATRI

Jan 8 2018 10:15AM