In this situation, are you allowed to overtake several vehicles at once?

In the video you are driving in the left lane of a motorway under a flyover and overtaking a line of lorries driving one behind the other in the right lane. You are allowed to overtake several vehicles without returning to the right lane between them. The answer is: yes.

The Road Traffic Act requires you to drive as close as possible to the right-hand edge of the roadway, but no rule tells you to return to the right lane between the successive vehicles you are overtaking - you fulfil the duty to drive near the right-hand edge after completing the whole manoeuvre; if directly behind one vehicle there is another one that you also want to overtake, the manoeuvre is still going on, and you do not have to squeeze into the gap between the lorries. Before overtaking you make sure that you have visibility and space and that nobody is overtaking you, and during the manoeuvre you keep a safe lateral clearance. You return to the right lane only after passing the last vehicle in the line, when you can see the whole of it in the interior mirror, and you free the left lane when someone faster is coming from behind.

Legal basis: Art. 16 para. 4, Art. 24 para. 1 and 2 and Art. 2 point 28 of the Road Traffic Act (Prawo o ruchu drogowym)