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New Speed-Control Plan for Va. Beltway

Capital Beltway drivers are going to see a new type of speed limit sign between Springfield and the Wilson Bridge starting next week.

vsl%20sign%20outer%20loop3%20%282%29.jpg Signs will post variable limit. (Thomson)

The operations center for the bridge and interchange reconstruction project will be able to vary the speed limit depending on traffic conditions.

To Washington drivers -- not the most patient people -- the concept behind the Variable Speed Limit system may seem illogical: "We want you to slow down so you can move faster," says John Undeland, spokesman for the bridge project.

He demonstrates with rice and a funnel. When he dumps the rice into the funnel, the spout clogs and only a few grains emerge. When he pours more slowly, the rice flows smoothly through the funnel.

Since human beings don't behave themselves like grains of rice, this new system is going to take some education and practice -- and enforcement. But the goal is to reduce the sudden braking and lane changing that can bring traffic to a halt at a work zone.

First, the operators have to educate themselves. They'll be using computers that monitor road sensors and recommend adjustments in the speed limits when they detect congestion is building through the bridge-interchange zone. (The Telegraph Road interchange work zone will be the focus of concern over the next several years.)

The speed limits will appear on black and white road signs that will look very familiar, except for the electronic display in the center that will show the adjusted speed limit.

VSL%20computer%20screens%20%283%29.jpg Computer bank monitors traffic flow so operator can adjust limit. (Thomson)

Once it changes, it won't be reset for at least 20 minutes. The speed limit can range from 55 mph down to 35 mph through the Variable Speed Limit zone, though it maxes at 50 in the work zone at the Telegraph Road interchange.

At first, the system will be used overnight, when traffic is lightest. Once operators and police get familiar with it, they can use it during the day. That's when most of our commuters will first encounter the effects.

Using the road sensors, the system also will be able to alert drivers to the amount of time it's likely to take them to travel between Springfield and the bridge. Those travel times will be displayed on variable message boards.

If the $3 million, two-year project proves successful in improving safety and traffic flow, the program can be extended. It also could help on other highways where longterm construction is getting underway, such as the western side of the Beltway in Virginia where the HOT (high occupancy or toll) lanes are under construction. Or in the work zone for the I-95 widening project in Northern Virginia.

By Robert Thomson  |  July 24, 2008; 8:50 AM ET
Categories:  Driving  
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