TRB06-1126 Role and Application of Accident Modification Factors (AMFs) within the Highway Design Process

Over the last few years, there has been a greater emphasis placed by transportation agencies to incorporate safety within the highway design process. The main assumption is that a highway designed with explicit attention to safety could significantly reduce the frequency and the severity of crashes. One tool that is rapidly gaining in popularity is the use of accident modification factors (AMFs) to estimate the change in safety following the implementation of a countermeasure, a significant change in a geometric design element or a planned construction upgrade of a highway facility. Given the fact that AMFs will play a very important role in the coming years, especially with the forthcoming publication of the Highway Safety Manual (HSM), there currently exist no document that addresses how AMFs could potentially be used with the process to design highways. Consequently, there is a need to provide such information so that engineers and highway designers could make the full use of AMFs for this process. This paper describes the role and application of AMFs in the highway geometric design process. More specifically, the paper provides guidelines for applying these factors within the preliminary design stage, for assessing design consistency and for evaluating design exceptions. For each design application, a proposed procedure is described in details. Finally, an example is provided for each design application to better illustrate the description of the procedure. Lord & Bonneson