Complex sentence: But when the driver of the runaway train activated the alarm, the signallers had to turn all signals to red, but the pre-programming of tracks were disabled causing runaway train to go into Platform 2 instead of Platform 1.
Split into simpler sentences: But when the driver of the runaway train activated the alarm, the signallers had to turn all signals to red. This disabled the pre-programming of tracks and allowed the runaway train to go into Platform 2 instead of Platform 1.