The Effectiveness of using Variable Speed Limit on the Performance of an Interrupted Flow

Hamdi Al-Nuaimi, Ron Ayers, and Kathirgamalingam Somasundaraswaran


Interrupted Traffic Flow, Variable Speed Limit, VISSIM, Traffic Simulation


The urban traffic congestion is getting worse with ever increasing urban population and vehicle ownership. The long queues at intersections and blockage of traffic on urban arterial roads become routine during the peak hours. Interrupted traffic flow through signalised intersections and arterial roads have badly been affected by these occurrences. Thus this paper examines the possibility of employing variable speed limit (VSL) for upstream traffic during the peak period to improve the traffic performance through signalised intersections as well as in urban arterials. The micro simulation software VISSIM was used to examine a hypothetical road network under VSL application. An expected traffic flow near capacity condition was simulated several times to see the effectiveness. Results show that for a reasonable period of time, the VSL application to the upstream traffic improve the traffic performance at immediate downstream intersections in terms of vehicle delay (16%), average queue length (18%) and average number of stops per vehicles (16%), while intersections located far from the VSL application has no or little effect. Similarly, the arterial performances have also been improved for a short period of time on the immediate downstream link in terms of density (13%), space mean speed (10%) and traffic flow (2%), the effective is negligible on the links located far. In addition a slight improvement was noticed to the total journey time on the immediate link.

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