 When the Glasgow, Paisley, Kilmarnock and Ayr Railway was opened in 1840, the Ardrossan railway now became a branch line joining this new railway at Kilwinning, and the new line south from Kilwinning to Irvine crossed over the Doura branch line a short distance to the west of the Garnock bridge.In 1840 the line was regauged to standard gauge and connected with the Glasgow, Paisley, Kilmarnock and Ayr Railway at Kilwinning station.The permanent way was largely relaid with heavier equipment to accommodate locomotive operation, and the line was doubled.