Paper 460 FROM CONGESTION TO RELIABILITY EXPANDING THE HORIZON

Traffic congestion has many dimensions including intensity, extent, duration and reliability. • Conventional congestion analyses use Highway Capacity Manual demand-capacity-delay relationships for assessing performance of specific roadway locations or sections. Broader measures include applying differences or ratios between actual and desired travel times and speeds. • Reliability brings a new set of metrics to roadway performance calculations. While typical measures deal with averages, reliability deals with the ranges and distributions of travel times. It focuses on estimating the travel time rates that are not likely to be exceeded. • This paper gives some of the key metrics associated with reliability and shows how they differ from conventional congestion analysis. It draws upon and extends recent research efforts.