Journey time estimation using MIDAS loop data

MIDAS (Motorway Incident Detection and Automatic Signalling system) has been operational on a number of motorways as part of the Highways Agency´s traffic management system. To verify the accuracy of the existing algorithm for calculating journey times on the M25, video footage and ANPR data, taken from two gantries between Junctions 15 and 16, have been recorded as part of the monitoring of the Controlled Motorways section. Journey times for a range of vehicles have been obtained from this data and compared to the estimates of journey time obtained from the algorithm. In free flow, the algorithm is reasonably accurate. However, in congested conditions, journey times are underestimated. Two main reasons for this are believed to be difficulties with loop based systems when vehicle headways are reduced during congestion, and the use of time-mean speed rather than space-mean speed in the MIDAS data. This paper describes the work to date on the second of these issues, and highlights results key to identifying improvements in journey time calculations