Comparison of delay on arterials by simulation and highway capacity manual computations

A comparison of delay on arterials was made using simulation and Highway Capacity Manual (HCM) computations. An extensive set of cases was defined over a range of flow rates, free-flow speeds, and signals per mile. Delay was calculated on the basis of the HCM computation for the specified signal progressions. The same cases were run using a specially revised version of the NETSIM microscopic simulation model. Detailed analysis showed that the discrepancies were traceable to the progression factor (PF). Corrections can be made (and are outlined) but must be done with care. There are a number of complex mechanisms at work. The primary result of this study may be clarifying the insufficiency in the current PF algorithm. The expectation that a single multiplicative factor could provide the needed correction to a long-link random-arrival steady-state delay model (that is, the existing HCM delay model), so that it could be a network-based model for delay estimation, appears to be simply unrealistic. For these and other reasons, research is focusing on the creation of a time-varying intersection delay model, building from basic principles.