 The Caledonian Railway carried a heavy mineral traffic from coalfields in South Lanarkshire to Ardrossan Harbour for export.This traffic ran via Langside Junction in south Glasgow, and the heavy and slow trains caused congestion; their onward route was over the Glasgow, Barrhead and Kilmarnock Joint Railway, so that some of the income from the traffic passed to the rival G&SWR.The Caledonian would see a considerable advantage if a direct railway could by-pass these areas, and the nominally independent Lanarkshire and Ayrshire Railway was proposed.