New methodology for estimating reliability in transportation networks with degraded link capacities

The measurement of transportation network reliability is a complex issue because it involves both the infrastructure and the behavioral responses of the users. This subject is challenging because there is no single agreed-upon reliability measure. Sources of system unreliability include natural and man-made disasters, recurrent events that result from demand variation, and nonrecurrent events that affect network supply such as incidents, work zones, and weather conditions. This article introduces a new method for estimating the effect of travel demand variation and link capacity degradation on the expected reliability of a roadway network. The method is applied to a roadway network and results of travel time reliability and capacity reliability are presented. The new travel time reliability method is sensitive to the users' perspective since it reflects that an increase in segment travel time should always result in less travel time reliability. This method can be expanded to large scale networks.