This report examines a temporary traffic management system implemented in association with a work zone in Copenhagen, Denmark. Dynamic message signs and traffic detectors were deployed on freeways surrounding the work zone to support dynamic route information at diversion points and the implementation of variable speed limits (VSL). The temporary system was deployed in response to expected increases in accidents and congestion as a result of a roadway expansion project on the Køge Bugt Motorway where four lanes were expanded to six lanes between summer 2002 and summer 2003. The road construction project involved several changes in road geometry within the work zone.
Variable Speed Limits
The variable speed limit system deployed as part of this project was implemented to the south of the work zone, enabling the adjustment of speed limits for northbound vehicles approaching the work zone during the morning rush. DMS were also deployed on the southbound portion of the freeway, allowing speed limits to be adjusted in response to recurring afternoon congestion at an interchange at the southern end of the study area.
The VSL system experienced considerable technical difficulties during the deployment which likely had a negative influence on the impacts of the system. Problems included displaying incorrect speed limits for up to 18 percent of the morning rush hour periods, and difficulties in responding to congestion during the afternoon peak periods (DMS signs going blank, or displaying incorrect speed limits).
Review of speed data collected during peak periods collected for one week before and after deployment of the VSL system determined that motorists do reduce speeds in response to the dynamic speed limits, by amounts generally less than 5 km/h depending on vehicle speed prior to the signs. These small changes and the bigger speed adjustments made during periods of traffic congestion meant that speeds became more homogenous only under periods of heavy traffic and congestion.
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