Complex sentence: The reason for the move is that the platforms can currently only accommodate two car trains, and would need to be expanded by thirty metres for three car trains, and the curves either side of the station preclude extension work.
Split into simpler sentences: The reason for the move is that the platforms could only accommodate two car trains. They would need to be lengthened by thirty metres for three car trains but the curves either side of the station precluded extension work.