Case studies on estimating crash modification factors for treatment combinations with empirical investigation of dual rumble strip application in Ontario

Crash modification factors (CMFs) are used to quantify the impact of safety treatments. These treatments are often used in combination and so the need for estimating CMFs for simultaneous applications arises. Applications of new heuristic methods in combining treatments showed mixed results, indicating a need for sound judgement in their usage. A case study for centreline and edgeline rumble strips on Ontario highways resulted in combined CMFs of 0.805, 0.79, 0.743, 0.799, and 0.689 for total, injury, PDO, single vehicle, and approach & sideswipe crash types, respectively. The estimates were comparable to the CMFs estimated in other research for actual dual rumble strip application. CMFs developed separately for tangent and curved segments showed that both rumble strip types are more effective on curved segments.