Methods for Identifying High Collision Concentrations for Identifying Potential Safety Improvements: Development of Advanced Type 2 Safety Performance Functions

This research developed advanced type 2 safety performance functions (SPF) for roadway segments, intersections and ramps on the entire Caltrans network. The advanced type 2 SPFs included geometrics, traffic volume and hierarchical random effects, while including random parameters for the geometric and traffic volume effects. Hierarchical random effects for roadway segments included route class, district and county effects. Random parameters for highway geometrics typically included design speed, median width, and shoulder width effects. In the case of intersections, advanced type 2 SPFs included traffic control, ADT and roadway geometrics, with channelization, two-way flow, and lighting variables as random parameters, and SPF class, mainline, functional class, intersection type, lighting, left turn channelization, mainline flow hierarchies as random effects. For ramps, type 2 SPFs included variables related to metering, HOV lane presence and ramp configuration, with county, and route class and district as hierarchical random effects. Model selection was conducted on the basis of information criteria such as AIC and BIC, and a comparative assessment of the suitability of basic type 2 SPF versus advanced type 2 SPFs was completed. The assessment indicated that basic type 2 SPFs were preferred in general for rural road segments, while advanced type 2 SPFs were preferred for urban segments.


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; References; Tables;
  • Pagination: 84p

Subject/Index Terms

Filing Info

  • Accession Number: 01641896
  • Record Type: Publication
  • Report/Paper Numbers: CA16-2446
  • Contract Numbers: 65A0508
  • Created Date: Jul 26 2017 1:34PM