They can be used to slow down cars heading into a traffic jam to reduce the arrival rate so the traffic jam can dissolve. Roads with a lower speed limit also fit more cars (need less safety distance) - driving slower means less traffic, so traffic jams can be avoided by reducing the speed limit.
These systems are very wide spread in Germany, covering most Autobahns around major cities.
They can be used to slow down cars heading into a traffic jam to reduce the arrival rate so the traffic jam can dissolve. Roads with a lower speed limit also fit more cars (need less safety distance) - driving slower means less traffic, so traffic jams can be avoided by reducing the speed limit.
These systems are very wide spread in Germany, covering most Autobahns around major cities.