Complex sentence: The vehicle involved was no. W2437, a British Railways Mark 1 coach which was built in 1960, at which time trains in the UK were mostly hauled by steam locomotives, which provided steam for heating passenger accommodation.
Split into simpler sentences: The vehicle involved was no. W2437, a British Railways Mark 1 coach which was built in 1960. At this time, trains in the UK were mostly hauled by steam locomotives, which provided steam for heating passenger accommodation.