When is it permissible to drive in the left lane on the Autobahn?

Driving in the left lane on the Autobahn is permissible primarily when overtaking another vehicle. The left lane is designated for faster moving traffic, and it is meant for overtaking slower vehicles on the right. Once you have completed the overtaking maneuver, it is expected that you return to the right lane to allow faster vehicles to pass. This practice helps maintain a smooth flow of traffic and enhances safety on high-speed roads.

The other choices present scenarios that do not align with the regulations for driving on the Autobahn. Driving in the left lane for any reason could lead to congestion and obstruct other drivers who may need to overtake. Similarly, driving only when there is no traffic does not justify the use of the left lane, as that lane must be reserved for faster-moving vehicles regardless of traffic conditions. Lastly, driving slower than the speed limit in the left lane contradicts the purpose of that lane being for overtaking, as it should be used by vehicles traveling at or above the speed limit, especially when faster vehicles are already present in the right lane.