Complex sentence: The line was closed to passenger rail traffic with a down turn of passengers in the early 1980's but stayed open to freight traffic for Sims Metal, but when this was then switched to road traffic the line closed.
Split into simpler sentences: The line was closed to passenger rail traffic with a down turn of passengers in the early 1980's but remained open to freight traffic for Sims Metal. However, when this was then switched to road traffic the line closed.