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Going With Flow on Beltway

We've seen systems that control traffic flow through stop and go lights on ramps or through speed limits that change with the time of day. But the Variable Speed Limit program scheduled to begin tonight on the southeastern side of the Capital Beltway in Virginia is new and different.

Will it work? The key to success is whether drivers will obey signs telling them to slow down when the highway around them still looks relatively open. If they do, traffic should flow more smoothly through the work zone that reduces lanes around Telegraph Road. If they don't, it will be hurry-up- and-wait for years to come.

This letter is from a reader who noticed our Commuter page feature on Sunday about the new speed-control program and how such efforts succeed or fail.

Dear Dr. Gridlock:
I have long tried to adjust my driving speed to anticipate traffic flow fluctuations ahead of me. This creates buffering that minimizes brake and acceleration fluctuations for vehicles behind me. Fluctuations (modeled in physics as turbulent flow) are an important component causing traffic flow oscillations, as well as increasing gasoline consumption.

The downside is that there are too many drivers whose personal time is more important than that of other drivers. These people all too frequently speed up to cut into empty space between cars, and then need to brake hard, disrupting traffic flow. If more drivers were not so aggressive and creating flow turbulence, we would have reduced commuter times.

Monitored and appropriately reduced speed limits provide increased time buffering, another good approach that can be tuned to achieve benefits for commuters.
Ronald Sheinson
Silver Spring

Most of you won't experience the Variable Speed Limit for a while, because the Wilson Bridge Project will begin by using it only at night, when traffic is lightest. But if you look at this link, you'll see what information will be provided to drivers about highway conditions. The information on traffic conditions and travel times will be available 24 hours a day, and could help you plan your trips.

By Robert Thomson  |  July 28, 2008; 8:58 AM ET
Categories:  Wilson Bridge  
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In response to the contributor from Silver Spring, it is not a civic responsibility to control traffic flow. Both Virginia and Maryland law says if you are moving at a rate of speed such as to impede the flow of traffic you are to move right. First of all it does not work. Second of all it is illegal. Traffic is more like a non-Newtonian fluid. Like red blood cells in an arteriole or capillary. The red blood cells line up and move at speed. If there is a slowdown then you have turbulence and blockages.

Posted by: Sivad | July 28, 2008 10:45 AM | Report abuse

To add to Sivad's blood cells don't have insurance policies with $500 deductables. Thus, what works with red blood cells or other fluids isn't necessarily applicable to traffic.

Posted by: Woodley Park | July 28, 2008 12:31 PM | Report abuse

And more importantly, I drive too fast because I am more important than you.

Suck it b1tch.

Posted by: Sivad | July 28, 2008 4:41 PM | Report abuse

The fluctating speed limits are a nice idea but they breed a society of drivers that don't know how to drive but know how to read signs and don't think. It is becoming more frequent that people rely on a sign to tell them what to do as opposed to putting thought of what the driving conditions and the speed that should be put.

The reason for the traffic conditions being so poorly during rush hour is not due to aggressive driving, although it doesn't help. It is primarily due to the lack of capacity of current roads. Cars and drivers have increased every year but the road capacity does not keep up at the same rate of growth. Instead of spending money on signs they should spend the money on increased roads.

At the same time I look at speed limits and laugh because they are rarely applicable. During rush hour the amount of cars on the road dictate and force everybody to go extensively slower then the speed limit. At the same time when traffic is light people tend to go faster then the limit or "speed." That is the ideal circumstances that is when speeding should be acceptable when there is lack of interference or possible harm to others.

Posted by: Vladimir | July 30, 2008 8:43 PM | Report abuse

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