Estimation of Critical Occupancy Values for Uk Motorways from Traffic Loop Detectors

Occupancy is the percent of time a traffic loop detector embedded in the road pavement is occupied by vehicles. This term is usually used as a substitution for the traffic density which is not feasible to obtain from detectors. One of the recent applications for the traffic occupancy is in calculating the timing for traffic signals on motorway entrances (Ramp Metering, RM). Most of the existing algorithms for RM assume that these devices will not operate until the traffic occupancy upstream or downstream from the merge area exceeds a specific value called “critical occupancy”. This paper focuses on estimating the critical occupancy using Motorway Incident Detection and Automatic Signalling (MIDAS) data. The data is taken from loop detectors located on three motorway sites in the UK. The results are compared with corresponding values as adopted by the Highways Agency for these sites to operate the ramp metering. The results show that the values which are currently used to operate the ramp metering devices in these sites are higher than those obtained from analysing the data. This will cause delays in the operation of the RM until the starting of traffic congestion which ultimately causes reduction in motorway capacity.