on the night of the accident southbound line was closed for maintenance work at the "brühl güterbahnhof" (brühl goods/freight station) north of the passenger station. trains going south switched to the opposite (northbound) line at hürth kalscheuren. since the entry signal at brühl could only show a green-yellow (hp2, "proceed with low speed") aspect when the route switched to the main signals in the freight station part (the opposite track didn't have any "destination signal" from the view of the tower like the other tracks have), all trains on the left track received a substitute signal "zs1", limiting the speed to 40 km/h till the next main signal. two slow orders had also been issued to drivers, restricting speed in the area to: