In the presented situation, before driving onto the rails, are you obliged to make sure that no rail vehicle is approaching?

In the video, you are approaching a level crossing with half-barriers; you pass sign A-9 with plate T-1 "20 m", the half-barriers are up, the traffic lights are not flashing, and before the tracks there is sign B-20 STOP. Before driving onto the tracks, you are obliged to make sure that no rail vehicle is approaching. The answer is: yes.

The Road Traffic Act requires a driver approaching and driving across a level crossing to exercise particular caution, and before driving onto the tracks to make sure that no rail vehicle is approaching and to take appropriate precautions. Raised half-barriers and traffic lights that are off do not free you from this obligation, because the equipment may be faulty. You stop at the STOP sign, look both ways along the tracks, and only then do you drive across.

Legal basis: Art. 28 para. 1 of the Road Traffic Act (Prawo o ruchu drogowym); § 21 para. 1 and 4 of the Regulation on road signs and signals