A Novel Approach for Estimating Crash Modification Factors: Jointly Modeling Crash Counts and Time Intervals between Crashes

Crash modification factors (CMFs) play important roles in roadway safety management. Safety analysts have proposed various methods for developing CMFs, and nearly all of them are crash count-based. Intervals between crashes are not considered, while survival theory has been widely used in other fields. The objective of this study is to incorporate survival models into the estimation of CMFs and to examine if it increases estimation accuracy. To accomplish the objective, this study proposed a joint modeling approach, simultaneously analyzing crash counts and time intervals between crashes, for estimating CMFs. In order to assess the performance, this study developed CMFs for a dummy treatment at 90 sites on rural two-lane highways in Texas, with the standard empirical Bayes (EB) method and the joint model, separately. The findings are very interesting: (1) The standard EB method tends to over-estimate the CMFs for the treatment, and under-estimate the standard error of the CMFs. Most of the cases, the results are biased; (2) The CMFs developed with the joint model have greater standard errors, but their values are closer to the true effects, which is more realistic; (3) Temporary instability in traffic crashes are also observed in this study. Increasing the duration of study period does not always increase the accuracy of CMF estimates. Roadway agencies are encouraged to deploy the joint model for dynamical monitoring safety effects of treatments by flexible feedback.

  • Supplemental Notes:
    • This paper was sponsored by TRB committee ANB25 Standing Committee on Highway Safety Performance.
  • Corporate Authors:

    Transportation Research Board

  • Authors:
    • Wu, Lingtao
    • Meng, Yi
    • Kong, Xiaoqiang
    • Zou, Yajie
  • Conference:
  • Date: 2019


  • English

Media Info

  • Media Type: Digital/other
  • Features: References;
  • Pagination: 6p

Subject/Index Terms

Filing Info

  • Accession Number: 01698341
  • Record Type: Publication
  • Report/Paper Numbers: 19-03454
  • Files: TRIS, TRB, ATRI
  • Created Date: Dec 7 2018 9:52AM