A pilot test for a variable maximum speed limit in the Netherlands that began last month is using photo enforcement to cite violators, in an effort to encourage drivers to observe posted speed limits. This test updates a Dutch variable-speed pilot-test 7 years ago that was unsuccessful because many drivers failed to observe posted speeds.



The new pilot test, which is called "Slim Rijden" (translation: "Intelligent Driving"), began September 4, 2002 on a 12 kilometer stretch of the A1 highway, a four-lane roadway on the Eastern side of the Netherlands near the city of Deventer. (The A1 highway links the Netherlands to Germany.) The pilot test, which is administered by the Dutch Ministry of Transport, Public Works, and Water Management, displays one of two speeds -- 80 km/hr or 100 km/hr -- on electronic matrix signs spaced every 500 meters along that roadway segment. Speed enforcement is accomplished by four digital cameras spaced every 2 km in that segment that track individual vehicles by photographing their license tags, and drivers are issued speeding tickets if the average speed in a 4 km segment exceeds the posted variable speed limit.



Speed-limit violators in the Slim Rijden test roadway do not receive immediate notice that they were caught speeding; tickets are typically received in the mail two weeks after each recorded violation. A broad awareness campaign, involving newspaper coverage, flyers at gas stations, and roadway signs was used to inform drivers of the test and the possibility that they could be cited for speeding.



The Slim Rijden pilot test is more complex than the Dutch variable speed-limit test seven years ago. "We have a rather sophisticated algorithm that looks at current speeds and traffic density," explains Hans Bokma, a Consultant to the Highway Engineering Division of the Ministry's Transport Research Centre, which is responsible for evaluating the test. "We want to know the impact of this variable speed test on roadway capacity, safety, and air pollution," he adds.



Slim Rijden is being deployed as an overlay onto the MTM ("Modeway Traffic Management") signal system, which is used on many congested freeways throughout the Netherlands to improve roadway safety. MTM encompasses both loop detectors and matrix signs every 500 meters, and warns traffic of incidents or other problems up ahead with flashing signs and a reduced recommended speed, typically 50 km/hr or 70 km/hr.



While the MTM system provides a ready-made infrastructure for the variable speed pilot test, it also contributes to driver confusion. "We distributed questionnaires to road users and drivers, and they said 'man, we see all kinds of speeds on the road,'" says Bokma. "Normally the software for the pilot test controls the speed displays, but the MTM system overrules the pilot whenever it needs to display its own speed. Therefore, the driver can see four different speeds -- 50, 70, 80, or 100 km/hr," he explains.



Bokma says that the first two weeks of the pilot test "were terrible," with more traffic jams than normal on that 12-km section of A1. "We made some mistakes, which we had to correct in the first two weeks," he acknowledges. He says that the pilot test algorithm, which attempts to anticipate the onset of a traffic jam, was likely "too flexible" at the start of the test and has been modified accordingly. He says that the goal of the pilot test was a 5% increase in roadway capacity, which has not yet been achieved. "We hope to get the chance to adjust the algorithm again to reach that 5%," he says. The results of the initial pilot test, which concludes on October 25, 2002, should be available in January 2003. However, the overall pilot test runs through April of next year, which could enable evaluations of further algorithmic modifications.



Author: Jerry Werner




Hans Bokma can be reached at: [email protected]