3 Speed Management
3.2.10 Variable Speed Limit System – A2 Motorway - Netherlands
The information on the A2 VSL System was obtained from the report Examples of Variable Speed Limit Applications.(6)
Impetus for the Activity
The impetus for the deployment of the VSL system was a desire to create uniformity of speeds and volumes within and between lanes, and thereby reduce the risk of shock waves, crashes, and congestion.
Description of the System
The VSL system was installed in 1992 on a rural section of the A2 Motorway between Amsterdam and Utrecht, and it is currently active. The system covers 20 km with VSL signs spaced approximately every 1 km. System inputs are measured using loop detectors, which are spaced every 0.5 km, and the system has automatic incident detection capabilities.
The standard posted speed limit is 120 km/h, and the variable posted speeds are 50, 70, and 90 km/h. The posted speed is determined by a system control algorithm based on 1-minute averages of speed and volume across all lanes. If an incident is detected, a speed of 50 km/h is displayed. If the speeds are posted with a red circle, they are enforced by photo radar. If posted without the circle, they are advisory.
System Performance
No problems with system performance were reported.
System Effectiveness Evaluation
The effectiveness of the system has been formally evaluated. The majority of drivers interviewed said they adjusted their speed due to the VSL signs. In general, drivers complied with the speed limit signs. The severity of shockwaves and speed in all lanes were reduced by the speed control measures.
No information was provided on the effect on the frequency or severity of crashes.