Effects of dynamic speed limits

The Dutch motorways become more and more congested because of the increasing mobility. The ambition of the national road network policy is to achieve more flexibility and increased performance of the existing road network. A possible way to do this is the use of dynamic speed limits. In this way, speed limits can be adjusted to unexpected situations such as weather conditions, congestions or incidents. Dynamic speed limits provide more flexibility than permanent speed limits. They offer a speed limit that matches with expectations of motorists and can take into account  the actual conditions of traffic, road, weather or the environment. Currently, dynamic speed limits are applied to a limited extent, e.g. when incidents occur or when road works are in progress. It is felt that dynamic speed limits may be useful for a larger number of applications than currently applied in the Netherlands.

At the moment, different applications with dynamic speed limits are being tested under the DYNAMAX (DYNAmische MAXimumsnelheden) program in the Netherlands. Also in other countries there have been a lot of experiments with dynamic speed limits. However, most of these projects have an effect on the homogenization of speeds and give no improvement of traffic flow efficiency, for example, in the sense of reduced travel times. In order to say something about the extended range of implementations of dynamic speed limits it is useful to know why an application gives an improvement of the traffic flow or not. The objective of this research is to develop a method to select suitable locations for the implementation of dynamic speed limits to improve traffic flow efficiency and to make the application suitable for that specific location. Also, it must be possible to predict the efficiency of the application before implementation. The method will be tested in a case study.

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