Variable speed limits have safety benefits and a homogenizing effect, but a German study found no increase in freeway capacity.

A with/without study analyzing variable speed limits on a three-lane freeway near Munich, Germany.

January 13, 2013

Summary Information

This paper presents findings of an empirical study focusing on the traffic flow effects of a variable speed limit (VSL) system on a three-lane German Autobahn. It integrates loop detector data as well as VSL and driver information data provided by means of overhead dynamic message signs along a 16.3-km section of Autobahn 99 near Munich, Germany. These data sources allow for a "with and without" analysis reflecting traffic flow and driver behavior in the presence of as well as in the absence of the VSL system deployment. In addition to speed, the primary features of interest were the spatial-temporal extend of the queue (congestion), the flow changes caused by identified bottlenecks, the distribution of flow across lanes, the percent trucks per lane, as well as the flow homogeneity between lanes.

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Empirical Assessment of Traffic Management Effects of a Variable Speed Limit System on a German Autobahn: Before and After

Author: Simone Weikl, Klaus Bogenberger (Munich University of the Federal Armed Forces), Robert L. Bertini (Portland State University)

Published By: Transportation Research Board

Source Date: January 13, 2013



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Goal Areas


Typical Deployment Locations

Metropolitan Areas


VSL, managed lanes, variable speed limits, vsl, safety, freeway management

Benefit ID: 2016-01070