Determining the sample size of probe vehicles in different traffic conditions on freeway

This research aims to investigate the required sample size of probe vehicles that are necessary to report the real-time travel time with a desired statistical accuracy in different traffic conditions on freeways. The corridor studied is SR78-E in the North County of San Diego that connects Oceanside and Escondido. The field data used in this study was collected from PeMS during the period from 0:00 A.M. to 12:00 P.M. (11/19/2014). Based on the corridor information and traffic volume data, this study uses VISSIM to create the simulation scenarios to generate probe vehicle (PV) data for analysis. The relationship between traffic volume under different traffic conditions and required sample size has been studied. The results indicate that the percentage of PVs have some influence on data volume which, in turn, affects the accuracy of the data; To obtain the same accuracy data, small percentage of PVs is required in more congested traffic conditions while large percentage of PVs is needed in lighter traffic conditions; In order to obtain the same accuracy of traffic data, the number of PVs needed in congestion condition is more than that in lighter traffic condition though the percentage of PVs is higher in the latter condition than the former one.