Probe vehicle: a comparison of motorway performance measure with other motorway flow detection techniques

During the last five years a number of high profile projects have been undertaken using floating 'probe' vehicles (PV), where vehicles equipped with on-board intelligent systems can receive information on likely travel times, congestion ahead, etc., and perhaps more importantly, transmit information relating to the vehicle status, location and speed, that may be used for network management purposes. Within the scope of the Road Traffic Adviser (RTA) project, it has been possible to obtain motorway performance data from PV and this data has been used to compare flow and travel time estimates with those from induction loops and number plate matching. The results describe: an analysis of the advantages and disadvantages of the systems, i.e. which measurements can or cannot be usefully obtained by each system; analysis of different measures in terms of variability, reliability and consistency; the development of a flow-time-distance diagram; and how detailed speed profiles derived from a probe vehicle could provide real travel time estimates and accurately locate incidents or congestion.