This report outlines a novel approach taken to characterise the variability in traffic throughput prior to the onset of congestion by investigating factors that could potentially affect capacity. Two motorway sites experiencing recurrent congestion in the UK were selected for investigation, the M4 eastbound between junctions 19 and 20, and the M25 anti-clockwise between junctions 11 and 12. The factors assessed include merge and diverge flows upstream and downstream of the congestion seedpoint, HGV flows, precipitation and lighting conditions. Capacity was defined as the 15 minute throughput prior to the onset of congestion, and all other factors were measured for the same 15 minute period. Multiple linear regression analysis revealed an R2 value of 0.46 at the M4 site and 0.27 at the M25 site. This demonstrates that the methodology developed shows some merit and that further investigation is warranted where higher resolution data should be used and more parameters should be considered. The potential application of this research lies in the operation of traffic management schemes such controlled motorways, where speed limits could be set based on a number of factors, such as those investigated above.

Want to know more about this project?