 This is one of Northern Ireland's most important arterial routes, as the road runs between its two largest cities and urban areas.Between Randalstown and Derry the road forms part of European route E16.In inner-city north Belfast the A6 route begins at Carlisle Circus at a roundabout with Clifton Street and the Crumlin Road (A52), and runs up the Antrim Road past Belfast Royal Academy and the Waterworks, towards Belfast Castle, Cave Hill and Belfast Zoo through Glengormley.