Traffic Flow at a Freeway Work Zone with Reversible Median Lane

Abstract

Work zones on freeways usually affect the quality of service for road users. Aiming to reduce traffic flow disruptions to a minimum, Hessen Mobil – Road and Traffic Management installed an innovative reversible lane system in a work zone on Autobahn A 3 south-east of Frankfurt, Germany. The section with three lanes and temporary hard shoulder running in both directions carries a high amount of commuter traffic with considerable fluctuations in peak traffic flow direction. During road works, four lanes in the peak direction and three lanes in the non-peak direction could be maintained through the use of a reversible lane system. The paper discusses the effects of the reversible lane system on traffic flow and road safety. Radar measurements revealed a maximum traffic volume of roughly 1500 veh/h on the reversible lane, which is around 25% of the total traffic volume during peak hours. The capacity of the work zone was estimated with the stochastic capacity estimation technique based on models for censored data. Compared with the capacity of the unaffected three-lane carriageway with temporary hard shoulder running, a decrease of the capacity by 14% to 17% was estimated for the four-lane work zone configuration including the reversible lane, depending on the direction. The difference between the capacities in both directions can be explained by the different lane geometries at the respective beginning of the work zone, leading to a higher number of lane changing manoeuvers directly upstream of the lane diverge in one direction. The traffic flow analysis also yielded a considerable impact of the work zone on peak hour traffic demand volumes, which were reduced by approximately 1000 veh/h. Similar to other freeway work zones, the road safety analysis revealed an increase of accident rates during road works. However, based on police accident reports only 10% of the total number of accidents and none of the severe accidents could be linked to particular features of the reversible lane system. Altogether, the investigation shows that a reversible lane system is a useful, safe and accepted instrument of intelligent traffic management for freeway work zones with high fluctuations in peak traffic flow direction. At the analyzed work zone, estimated travel time losses of 400000 veh*h could be saved during two months of road works by the application of the reversible lane compared with a permanent lane reduction in one direction.