Impacts of sensor spacing on accurate freeway travel time estimation for traveler information
Robert L. Bertini and David J. Lovell
Journal of Intelligent Transportation Systems, Vol. 13, No. 2, pp. 97–110.
ABSTRACT
Travel time estimation is a critical ingredient for transportation management and traveler
information—both infrastructure-based and in-vehicle. Infrastructure managers and operators are
interested in estimating optimal freeway sensor density for new construction and retrofits.
Focusing on freeway travel time estimation for display on roadside variable message signs, this
paper describes a concept developed from first principles of traffic flow for establishing optimal
sensor density. The method is based on computing the magnitude of under- and overprediction of
travel time during shock passages when using the midpoint method. Two case studies are
presented considering representative traffic dynamics situations. Along with other performance
metrics, 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 recurrent and nonrecurrent congestion are included. Finally some suggestions for future
research are described.