Toward optimal sensor density for improved freeway travel time estimation and traveler information

Accurate freeway travel time estimates are critical for transportation management and traveler information-both infrastructure-based and in-vehicle. Infrastructure managers are interested in estimating optimal freeway sensor density for new construction and retrofits. This paper describes a concept developed from first principles of traffic flow for establishing optimal sensor density based on the magnitude of under- and over-prediction of travel time during shock passages when using the midpoint method. A suggested aggregate measure developed from vehicle hours traveled (VHT) is described for a reasonable range of detector densities. Extensions of the method to account for both recurring and nonrecurring congestion are included. Finally some suggestions for future research are described.