Results of field trials with dynamic speed limits in the Netherlands: Improving throughput and safety on the A12 freeway

In the past few years, field trials with dynamic speed limits have been carried out on the Dutch freeway network. This paper discusses the tests at one of the field trial locations. On this location two test were carried out; the speed limit was lowered when there were congestion problems and during heavy rain. The field trial lasted for six months. Two new algorithms were developed to determine when the speed limit should be changed: an algorithm that uses real-time precipitation radar data to advise appropriate speed limits during heavy rain, and the SPECIALIST algorithm for resolving shockwaves. The field trials were evaluated using loop detector data as well as camera data. Changes in driver behavior, traffic flow characteristics, traffic safety, air quality and noise levels were analyzed. Also, a user acceptance study was carried out. The evaluation showed that dynamic speed limits can be applied to achieve policy objectives, such as improving throughput and traffic safety. Road users appreciate the dynamic speed limits and adapt their behavior accordingly. Undesired side effects were shown to be very limited to nonexistent.