Can you begin an overtaking manoeuvre under the flyover?

In the video you are driving in the right lane of a motorway and approaching a flyover that passes over the roadway; a vehicle is driving in the distance ahead of you, and the left lane is free. You are allowed to start overtaking under the flyover. The answer is: yes.

The provisions of the Road Traffic Act list the places where overtaking is prohibited: bends marked with warning signs, the tops of hills, junctions (with exceptions), level crossings and tram crossings, pedestrian crossings and cycle crossings. A flyover over the road is not on this list - driving under a structure does not change anything about visibility or the traffic arrangement, and on a motorway there are no junctions at the same level, so this place is not a junction. On a motorway you overtake only in the left lane, after making sure that it is free for a long enough distance and that nobody behind has started overtaking you, and after signalling the manoeuvre with the left indicator. A ban on overtaking could apply here only because of sign B-25, which is not in the video. It would be different in a tunnel, where signs often prohibit changing lanes, but a flyover over the road is not a tunnel.

Legal basis: Art. 24 para. 1, 2 and 7, Art. 26 para. 3 point 1, Art. 27 para. 4 and Art. 28 para. 3 point 3 of the Road Traffic Act (Prawo o ruchu drogowym)