autobahn system (LKW-Maut). The German government contracted with a private company, Toll Collect GmbH, to operate the toll collection system, which has involved the use of vehicle-mounted transponders and roadway-mounted sensors installed throughout Germany. The toll is calculated depending on the toll route, as well as based on the pollution class of the vehicle, its weight and the number of axles on the vehicles. Certain vehicles, such as emergency vehicles and buses, are exempt from the toll. An average user is charged €0.15 per kilometre, or about $0.31 per mile (Toll Collect, 2007). Traffic laws and enforcement Driving in Germany is regulated by the Straßenverkehrs-Ordnung (road traffic regulations, abbreviated StVO). Enforcement on the federal Autobahnen is handled by each state's highway patrol (Autobahnpolizei), often using unmarked police cars and motorcycles and usually equipped with video cameras, thus allowing easier enforcement of laws such as tailgating. Notable laws include the following. The right lane should be used when it is free (Rechtsfahrgebot) and the left lane is generally intended only for overtaking unless traffic is too dense to justify driving only on the right lane. It is legal to give a short horn or light signal (flashing headlights or Lichthupe) in order to indicate the intention of overtaking, but a safe distance to the vehicle in front must be maintained, otherwise this might be regarded as an act of coercion. Penalties for tailgating were increased in May 2006 to a maximum of €375 (now €400) and three months' license suspension: "drivers must keep a distance in metres that is equal to half their speed. For example, a driver going 100 km/h on the autobahn must keep a distance of at least 50 metres (165 feet)". The penalty increase followed uproar after an infamous fatal crash on Autobahn 5 in 2003. In a traffic jam, drivers must form a rescue lane (Rettungsgasse) to allow emergency services to reach the scene of an accident. This emergency corridor is to be created on the dividing line between the two leftmost lanes; following the guiding principle of if on the left, drive left, else drive right, vehicles may cross into another lane if need be. It is unlawful to stop for any reason on the autobahn, except for emergencies and when unavoidable, like traffic jams or being involved in an accident. This includes stopping on emergency lanes. Running out of fuel is considered an avoidable