Is it permissible to drive at a speed that could make it difficult to stop the vehicle when the red signal starts flashing?

In the video you are approaching a level crossing in a town, with half-barriers and light signals which are not lit at the moment. Driving at a speed which could make it difficult to stop the vehicle at the right place when the red signal comes on is not permitted. The answer is: no.

The Road Traffic Act states that a driver is obliged to drive at such a speed that they can stop the vehicle in a safe place when a rail vehicle is approaching or when a safety device or a signal being given prohibits entry onto the level crossing. The flashing red signal at a level crossing comes on without warning - there is no amber as at a junction - and a moment later the half-barriers come down. If you are driving so fast that you cannot stop before the signal or the stop line, you are left with two bad options: stopping on the tracks or driving under a barrier which is coming down, and the Act prohibits both. That is why you choose your speed before a level crossing not for what you can see now, but for what may happen in a second: you slow down so that you can stop before the signal with a margin, and you watch the signal until you have crossed the tracks.

Legal basis: Art. 28 para. 2 and para. 3 point 1 and 2 of the Road Traffic Act (Prawo o ruchu drogowym)