To be noted : some signal boxes, like Katowice Zawodzie on track 2, have manual level crossings.
You have to close them before setting a route : click on the level crossing and select ZAMK.
After a few moments, the level crossing becomes grey on the screen and you can set the route.
You have to open them when the train has vacated the level crossing : click on it and select OTW.
It will then become magenta.