Upon passage of the rail vehicle, half of the barrier is lifted. Are you allowed in this situation to start driving on to the rail tracks?

No, entering the crossing is forbidden. According to Art. 28 of the Road Traffic Act, you may only drive onto the tracks once the barriers have finished rising and the red signal on the light has gone out. Entering the crossing while the barriers are still moving or the red light is on is extremely dangerous, as another train could be approaching.