Complex sentence: The platform was used on 3 or 4 occasions each year and closed in the mid- 1960s although it remained "in situ" until the early 1970s.
Split into simpler sentences: The platform was used on 3 or 4 occasions each year. The last trains to use the platform did so in the mid- 1960s when it effectively closed although it remained "in situ" until the early 1970s.