Traffic flow effects of a variable speed limit system on a German Autobahn: An empirical analysis

This paper presents findings of an empirical study focusing on the traffic flow effects of a variable speed limit (VSL) system on a 16.3-km section of the primarily three-lane Autobahn 99 near Munich, Germany. The available data sources allow for a detailed analysis reflecting traffic flow on one day with the VSL system deployment as well as on a day without the VSL system deployment. In addition to speed, the primary features of interest were the spatialtemporal extent of the queue (congestion), the flow changes caused by indentified bottlenecks, the distribution of flow across lanes as well as the percent trucks per lane. The analysis recorded bottleneck flow reductions across all lanes on the day with active VSL system, especially in the median and center lanes. On the day with the inactive VSL system the flow reductions were lower and only occurred in the right lane while there was a flow increase in the median lane. Further examination indicated a safety improvement on the "with" day.