- The Washington Times - Sunday, July 27, 2008

Nighttime drivers on the Capital Beltway near the Woodrow Wilson Bridge will soon encounter the latest in traffic-management technology - a speed limit that changes depending on the degree of congestion.

Virginia transportation officials hope the variable speed limit, which goes into effect Monday, will help avoid the funnel effect that occurs when lanes are closed for construction. The technology has been used successfully in Europe, but has had only limited trials in the United States, said Ronaldo T. Nicholson, who coordinates the Wilson Bridge and other major projects for the Virginia Department of Transportation.

“With the number of major interstate projects going on right now, we have to look at new technology,” he said.

When roads narrow, traffic slows and the potential for a rear-end collision increases.

That has been happening lately on a 2-mile stretch of the Beltway at Telegraph Road, on the Virginia side of the bridge, which connects to Maryland over the Potomac River. In the spring, the road was reduced from eight lanes to six, and construction will require additional short-term lane closures from 9 p.m. to 5 a.m.

Officials illustrated the problem Thursday by dumping rice into a funnel. Instead of the rice being pulled through quickly by gravity, much of it got stuck.

The idea of the variable speed limit is that if the grains of rice are poured gradually or vehicles approach slowly, all of them will get through more quickly.

Just how slow they need to go depends on the volume of traffic. Officials will monitor conditions using cameras and sensors along the road. If congestion occurs, they will lower the speed limit in increments of 5 to 10 mph.

The speed limit along the affected stretch will range from 35 mph to 55 mph and will be posted on signs that look like regular, white speed-limit signs, but with a light board in the middle.

State officials plan to use the technology first during only nighttime lane closures. If the technology is successful, they hope to deploy it near the Wilson Bridge during the day.

Mr. Nicholson said it also could be used around the region “for recurring congestion and definitely incident management.”

He pointed to Tysons Corner, where a large number of drivers try to get on the highway at once.

The biggest challenge will be getting drivers to slow down, said bridge project spokesman John Undeland.

Officials are using advertising and highway message boards to get drivers to pay attention to the fluctuating speed limits. And the Virginia State Police have promising an active enforcement campaign. In addition, the bridge Web site will have 24-hour, real-time traffic information - not just during lane closures.

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