Did safety experiment work?
In the spring, the Virginia Department of Transportation will complete an assessment of its effort to improve safety and traffic flow through the Wilson Bridge construction zone. The effort, called the Variable Speed Limit program, was an attempt to slow down traffic so that drivers would get where they were going more quickly.
It sounded like something against nature. In fact, it probably was. During my travels through the Capital Beltway work zone near Telegraph Road, it was not apparent that drivers were observing the electronic signs that displayed the current speed limit.
The maximum speed limit in the work zone was 50 mph. The Variable Speed Limit zone extended beyond that, covering most of the Beltway between the Springfield interchange and the Wilson Bridge. Along that stretch, the speed limit could be reduced to as low as 35 mph, depending on traffic conditions. If the monitors could see that traffic was severely congested around Telegraph Road, they could reduce the speed limit for drivers approaching the area.
If those drivers actually slowed down, they might not have to jam on the brakes when they encountered the congestion. Braking for congestion causes more congestion, and sometimes, it causes crashes. Think of sand pouring through a funnel. The slower the pour, the more sand gets through. Pour too fast and you can block the funnel.
The experiment is over. The speed limit throughout that portion of the Beltway has been restored to 55 mph, something drivers haven't seen since 2005, when the construction period intensified.
The contract for the speed limit program has expired, but the Wilson Bridge project also says that the continuing construction impact on the Beltway -- the reason for the program -- will no longer be as intense as what we saw during the earlier years of the building program.
I'll be interested in the results of the VDOT review of the program. If it worked, the Variable Speed Limit system could be used elsewhere. But I'd also like to hear from drivers who have traveled the Beltway since the program went full time in May 2009.
My take: Unlike grains of sand, drivers react in different ways to efforts to control their flow. Many -- probably most -- ignored signs intended to slow them down before they reached the serious congestion. Enforcement was always a key and always a problem. Anytime you set up a very visible enforcement zone, you create a new source of traffic congestion. Also, the Beltway is much more than a route for D.C. area commuters. It's also the East Coast Main Street. Many long-distance drivers never got familiar with the speed zone or its purpose.
February 23, 2010; 10:22 AM ET
Categories: Congestion , Construction , Driving , Safety , highways | Tags: Dr. Gridlock
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