Special Circumstances
One of the problems with static speed signs is that they can make no allowance for special circumstances. Variable speed signs on the other hand, have a distinct advantage. A study was done in the 90s in several European countries. In Germany, the autobahn served as the testing area. Since some areas of the autobahn have no speed limit. Germany concluded that using dynamic speed signs in some areas would be both affordable and save money, so much so that the whole system would be paid for within two to three years.
Using the Variable Speeds
These systems are now in place on many stretches of the autobahn. This system includes radar speed signs, variable speed signs, and even new ITS technology that can discern some types of weather and warn travelers of hazards on the road. These signs can even direct motorists to alternate routes when traffic is heavy to cut down on congestion. With over 800 miles of the German autobahn using these signs, it is clear that they are effective.
The Test
The purpose of the signs was to slow down traffic when conditions became dangerous, to decrease congestion, and to keep traffic speeds low when passing construction zones. The original estimation for the study was that the accident rate would drop by 20%. But the German government has estimated that since the signs were installed 3 years ago, the accident rate has droppe