A safety analysis of a specific location includes a "base crash rate" analysis for identifying crash patterns at the study location. If the calculated crash rate for any crash type at a particular location is found to be higher than the "base crash rate", then that location is chosen for further study to determine if a safety problem actually exists at that location and, if so, what counter measure(s) can be used. The primary objective of this study was to develop a set of mathematical models to estimate base crash rates for freeways in Ohio. The models estimate the incremental changes in the dependent variables (crash rate for different types of crashes)resulting from changes in the independent variables including geometric features, operational controls, and environmental conditions. The base crash density/rate models were developed for the following crash types: (a)Injury crashes, (b) PDO crashes, (c) Total crashes, (d) Angle crashes, (e) Fixed crashes, (f) Rear end crashes, (g) Sideswipe crashes, (h) Wet road crashes, and (i) Night crashes. To evaluate the complex interaction among the dependent and independent variables, Automatic Interaction Detection (AID) technique was used. After the completion of AID analysis, stepwise multiple regression technique was used to develop mathematical models for the split groups. Finally, the models were validated with the one-third data that was set aside for validation. This study developed state-wide and district-wide base crash density and rate models for freeways. These models are recommended for use by ODOT for evaluating freeway crashes. The results of this study have a high potential of implementation in Ohio.

Also available online via the Web pages of the TRB Cooperative Research Programs (www4.trb.org/trb/crp.nsf).

Technical summary of the FHA report FHWA-HRT-17-086 program that studied the safety performance of various stop-controlled intersections for the Evaluation of Low-Cost Safety Improvements Pooled Fund Study. This study evaluated the safety effectiveness of multiple low-cost treatments at stop-controlled intersections.

The Development of Crash Modification Factors program studied the safety performance of various stop-controlled intersections for the Evaluation of Low-Cost Safety Improvements Pooled Fund Study. This study evaluated the safety effectiveness of multiple low-cost treatments at stop-controlled intersections. Improvements included basic signing and pavement markings. This strategy is intended to reduce the frequency and severity of crashes at stop-controlled intersections by alerting drivers to the presence and type of approaching intersection. Geometric, traffic, and crash data were obtained at three- and four-legged, two- and four-lane major road, and urban and rural stop-controlled intersections in South Carolina. To account for potential selection bias and regression to the mean, an empirical Bayesian before-after analysis was conducted, using reference groups of untreated intersections with similar characteristics to the treated sites. The analysis also controlled for changes in traffic volumes throughout time and time trends in crash counts unrelated to the treatments. The aggregate results indicate reductions for all crash types analyzed (i.e., total, fatal and injury, rear-end, right-angle, and nighttime). The reductions are statistically significant at the 95-percent confidence level for all crash types. For all crash types combined, the crash modification factors (CMFs) are 0.917 for all severities and 0.899 for fatal and injury crashes. The CMFs for rear-end, right-angle, and nighttime crashes are 0.933, 0.941, and 0.853, respectively. The benefit-cost ratio estimated with conservative cost and service life assumptions is 12.4 to 1 for total crashes at unsignalized intersections. The results suggest that the multiple low-cost treatments, even with conservative assumptions on cost, service life, and the value of a statistical life, can be cost effective.

Improved cost-effectiveness techniques are developed for evaluating highway safety programs. These improved techniques include: better methods of determining accident costs; statistical procedures for calculating accident costs; consistent system for evaluating accident cost and countermeasure effectiveness; and improved incremental benefit-cost algorithm for ranking safety projects. In addition to developing improved cost-effectiveness techniques the report reviews selected accident countermeasure studies and provides a critique of current procedures for evaluating safety programs. Three techniques are recommended for use in allocating safety funds: incremental benefit-cost, with improved algorithm; dynamic programming; and integer programming.