In this situation, do you have the right to overtake the vehicle in front of you by driving onto the part of the road designated for oncoming traffic, if you can stop before the railway crossing?

In the photo a car is standing in front of you before a level crossing; the half-barrier is down and the signals are flashing red. You are not entitled to go around this vehicle by entering the part of the roadway for the opposite direction, even if you could stop before the level crossing. The answer is: no.

The Road Traffic Act prohibits a driver from going around a vehicle waiting for the level crossing to open if this would require entering the part of the roadway intended for traffic in the opposite direction. The car in front of you is waiting for the level crossing to open, and going around it would mean driving on the left side of the roadway - exactly what the rule prohibits, and regardless of the purpose: it does not matter that you only want to "stop closer" and do not intend to enter the tracks. The ban protects against several dangers at once: after the barrier goes up, oncoming vehicles will move off straight towards you, by standing in the left lane you block their way out of the level crossing, and the driver in front of you, when moving off, does not expect a car next to them. So you stop behind the waiting vehicle, in the queue, and move off only when it moves off, the barriers go up and the lights go out.

Legal basis: Art. 28 para. 3 point 4 of the Road Traffic Act (Prawo o ruchu drogowym)