The intent of this project is to develop safety performance functions for different types of facilities in North Carolina.
Two approaches for developing SPFs will be explored. One approach is to calibrate the predictive models in the HSM using data from a limited number of sites (for each facility type) from North Carolina. The second approach is to develop North Carolina-specific SPFs. The second approach is expected to provide more accurate results but will require data from a larger sample of sites, and also involve the application of state of the art statistical techniques such as negative binomial regression.
This project will also develop a method that NCDOT can use to develop the safety performance functions for future years. In addition, the project will also develop a guidebook to illustrate the most effective use of SPFs for decision making in North Carolina.
The objective of this effort is to develop safety performance functions (SPFs) for different types of facilities in North Carolina and illustrate how they can be used to improve the decision making process. The prediction models in Part C of the Highway Safety Manual were calibrated using data from North Carolina. SPFs were estimated for 9 crash types for 16 roadway types using statewide data from North Carolina; these SPFs just include AADT and can be used for network screening. In addition, SPFs for rural two lane roads were developed using AADT and other site characteristics including shoulder width/type and terrain. Using examples, this report outlines how the different SPFs can be used for network screening, project level analysis, and before-after evaluation using the empirical Bayes method. Finally, there is a discussion of how NCDOT can use the SPFs in the future by either calibrating the SPFs developed in this effort and/or develop SPFs using negative binomial regression. Along with the final report are Excel files that can be used by NCDOT to calibrate the SPFs in the future and to implement the HSM prediction methodology.