Estimation of Incident Propensity for Reliability Analysis in the Highway Capacity Manual

Abstract

This paper presents the method used to generate the incident probabilities required by the freeway scenario generator for travel time reliability analysis in the Highway Capacity Manual. The freeway scenario generator requires the estimation of monthly probabilities of different levels of incident severity during specified study periods. Incident probability in this context is the fraction of time that an incident of a specific level of severity is active somewhere on the freeway facility during the study period for the month considered. The proposed method is designed to recognize and deal with the varying levels of incident and facility data availability at the implementing agencies. A queuing model is proposed for the conversion of incident frequencies into incident probabilities when agencies have access only to frequencies instead of probabilities.