An alternative are variable speed limit systems: http://en.wikipedia.org/wiki/Speed_limit#Variable_speed_limits http://en.wikipedia.org/wiki/Speed_limit#Variabl

An alternative are variable speed limit systems: http://en.wikipedia.org/wiki/Speed_limit#Variable_speed_limits http://en.wikipedia.org/wiki/Speed_limit#Variable_speed_limi... 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.