A summary of a recent work in assessing the impact of management system options in terms of traffic operational conditions on the M25 between junction 16 and junction 21 during the peak period is presented. A range of modelling outputs was used to assess the merits of the alternative active traffic management systems. For each traffic management system, key indicators such as variability in journey time and traffic levels on the M25 and on approach roads were examined. In addition sensitivity tests were conducted into the variability of the micro-simulation. The GETRAM traffic micro-simulation suite was used to test the systems considered. The GETRAM package, consisting of a graphical editor TEDI, and the micro-simulator AIMSUN, was used to develop a model with the study area covering the motorway network in the north-west quadrant of the M25 between the M40 and the M1 corridors. The traffic flow demand data for the micro-simulation modelling was extracted from a larger separate calibrated/validated NAOMI version 5 SATURN model. The traffic demand flows were profiled over a three hour period of 07:00 to 10:00 hour period. The demand was disaggregated into different vehicle categories representing cars with 0, 1, 2 or more passengers, light goods vehicles with 0, 1, 2 or more passengers, and heavy goods vehicles (HGV). In addition a matrix of bus and coach services (PSV) was synthesised from service patterns and frequencies. The base year GETRAM model was calibrated to traffic flows and journey times in 2001 for the average morning peak period between 07:00 and 10:00 hours. The calibrated validated 2001 base year model was used to prepare a 2011 forecast year model, which was used for systems testing. The main findings of the study are listed. It was possible to identify the impact of the different active traffic management systems. Of the traffic management systems modelled on the M25 motorway between J16 and J21, the ramp metering system seemed the most effective in controlling traffic operations by promoting smooth traffic flows on the M25 active mainline. Of the systems considered the dedicated bus lane on the outside lane seemed to be the least effective. In congested traffic conditions, public transport vehicles found it difficult to weave across the congested three non-priority lanes, resulting in a low percentage usage of the dedicated public transport lane. The main line metering system performed poorly as it generated additional delays to all traffic, which were attributable to a number of reasons including weaving. For the covering abstract see ITRD E126595.
Abstract