This book presents a study of the use of GPS equipped probe vehicle to collect traffic data on a motorway network. Two types of GPS equipped probe vehicles, active and passive, have been studied. A passive probe vehicle was considered to provide only link journey time and a minimum number of probe vehicles is required for reliable estimation. This research has studied the distribution of individual journey times and calculated the sample size of probe vehicles required in different traffic conditions. The sample size has shown to be generally stable for the same link, but may decrease in...