Vehicles with a top speed less than 60 km/h (37 mph) (such as quads, low-end microcars, and agricultural/construction equipment) are not allowed to use the autobahn, nor are motorcycles and scooters with low engine capacity regardless of top speed (mainly applicable to mopeds which are typically limited to 25 kilometres per hour (16 mph) or 45 kilometres per hour (28 mph) anyway). To comply with this limit, heavy-duty trucks in Germany (e.g. mobile cranes, tank transporters etc.) often have a maximum design speed of 62 km/h (39 mph) (usually denoted by a round black-on-white sign with "62" on it), along with flashing orange beacons to warn approaching cars that they are travelling slowly. There is no general minimum speed but drivers are not allowed to drive at an unnecessarily low speed as this would lead to significant traffic disturbance and an increased collision risk.