Thursday, June 19, 2008

Variable Speed Limits - Test Case on the East Coast

An unstable speed limit:

ALEXANDRIA, Va. -- Should a computer tell you how fast or slow you should be driving on the road? Pretty soon that will be the case around the Woodrow Wilson Bridge.
A variable speed limit system will be set up on the Capital Beltway between the Springfield Interchange and the Telegraph Road Interchange, WTOP has learned. It will be turned on in late July.

Sensors and cameras will monitor traffic flow, then alert an operator in a control center to adjust speed limits to allow for a more gradual flow through the area. The basic concept is that by slowing traffic down, traffic will move in unison -- as opposed to a rush of cars hitting the same area all at once.

A recent report about this kind of system done for Utah's transportation department states, "Reducing the speed of individual drivers is important, however, reducing the variation of speed of all drivers in a section of roadway has an even greater safety enhancing effect. Crashes are not related as much to speed as to the range in speeds from the highest to the lowest. Studies show that, regardless of the average speed on the highway, the more a vehicle deviates from the average speed, the greater its chances of becoming involved in a crash."

There are similar variable speed limit systems in place in other parts of the country and in Europe, but the system around the Wilson Bridge is expected to be much more complex.

I always though Singapore had a pretty good traffic system:

The city center of Singapore is a restricted zone. This means that you will have to pay additional road tax to enter this area during working hours from Monday to Friday. Also, some sections of highways are restricted during rush hours. The additional road tax is paid by a system called Electronic Road Pricing, or ERP (so not Everyday Rob People as the occasional taxi driver would have you believe). Every car has an IU, or In-vehicle Unit, which is a device attached to the windscreen and which contains a cashcard. When entering the restricted zone, the ERP gantries will automatically deduct the tax from your cash card. Depending on which time you enter the zone, these charges can be anything from $0.50 to $2.50. More information about ERP can be found here.

From what I understand, each car has a monitor on it, similar to the Fastrak system here in Southern California. The exception being that you are charged per mile, and you are charged for every mile you go over the speed limit. And the speed limit and per mile charges adjust to how many cars are on the road.

Traffic congestion is costly, and freeways are not free.

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