When the Belfast & Ballymena Railway opened their line, the route ran from York Road in Belfast to Greenisland and a reversal was required to travel hence to Ballymena via Monkstown and Antrim town. In 1934, the Bleach Green Junction layout was built, providing a direct route to/from Belfast without reversal. The former mainline between Greenisland and Monkstown became a minor route, used only for boat traffic to Larne.