Roadside Geometry Effects on the Overdispersion Parameter
Safety performance functions (SPFs) are statistical models used to estimate crash frequencies for a specific site type with specific base conditions. Negative binomial (NB) models estimate an ancillary term that provides a correction for the dispersion heterogeneity in the data, but assume that the dispersion in the dataset is consistent across all segments. The heterogeneous dispersion NB allows segment specific parametrization of the ancillary parameter. This paper details a summary of these models, estimated for total crashes, and 31 different crash frequency classifications. Key findings of this research were that the roadside presence of a culvert, ditch, guardrail, tree or tree group led to segments having lower over-dispersion for total accidents. Roadway segments with guardrails, side slopes, or ditch extending between 90 and 100% of the length, exhibit more over-dispersion. The over-dispersion for fatalities on segments with a culvert or roadside ditch was found to be lesser than otherwise, but higher for segments with a roadside fence. Severe injury crashes were found to be dispersed higher for segments with guardrail lengths between 90 and 100%. Accounting for the effect of these roadside characteristics enables the identification of roadway segments with high or low propensities of specific crash types. By providing insight into roadside features that influence different types of crashes, while taking roadway geometry and traffic exposure into account, this work could provide the means for proactive approaches to roadway safety management.
-
Supplemental Notes:
- This paper was sponsored by TRB committee ANB20 Standing Committee on Safety Data, Analysis and Evaluation. Alternative Title: Heterogeneous Dispersion Parameter Negative Binomial Models Using Roadside Geometry
-
Corporate Authors:
500 Fifth Street, NW
Washington, DC United States 20001 -
Authors:
- Hariharan, Barad
- Hong, Jungyeol
- Shankar, Venky
- Venkataraman, Narayan
- Milton, John C
- Van Schalkwyk, Ida
-
Conference:
- Transportation Research Board 95th Annual Meeting
- Location: Washington DC, United States
- Date: 2016-1-10 to 2016-1-14
- Date: 2016
Language
- English
Media Info
- Media Type: Web
- Features: References; Tables;
- Pagination: 26p
- Monograph Title: TRB 95th Annual Meeting Compendium of Papers
Subject/Index Terms
- TRT Terms: Crash characteristics; Crash injuries; Crash rates; Fatalities; Geometric segments; Highway safety; Mathematical models; Roadside hazards
- Subject Areas: Highways; Safety and Human Factors;
Filing Info
- Accession Number: 01592878
- Record Type: Publication
- Report/Paper Numbers: 16-5892
- Files: TRIS, TRB, ATRI
- Created Date: Mar 7 2016 10:19AM