Complex sentence: The Platform is short and long trains overhang the platform and level crossing to the west of the station, until the platform can be lengthened selective door opening is used, where only the doors on the front unit will open.
Split into simpler sentences: The Platform is short and long trains overhang the platform and level crossing to the west of the station. Until the platform can be lengthened, selective door opening is used, where only the doors on the front unit will open.