Complex sentence: Trams operated along High Street until 1952, when the trams in Fremantle were replaced by buses, which were being taken out of service due to economic costs, and to relieve traffic congestion on roads.
Split into simpler sentences: Trams operated along High Street until 1952, when the trams in Fremantle were replaced by buses. The trams were taken out of service due to their economic costs and to relieve traffic congestion on roads.