This article is about the Class III road numbered C91 maintained by DfI Roads. For other roads numbered C91, see C91.
The C91 is a rather lengthy route. It starts on Union Street in Coleraine and heads south along the one-way Brook Street and Long Commons through the town centre. This leads to a T junction with Beresford Road where one can follow the one-way system either by turning left to reach Terrace Row or by turning right to reach Beresford Place, both of which are "clockwise" only one-way streets forming part of an inner ring road in the town. The C91 continues south from the ring road along Mountsandel Road, where it soon passes over a bridge crossing the A29 dual carriageway. Just beyond the bridge, the road also incorporates Rugby Avenue which acts as a link to the A26 and A29 roundabout. The road meets the first of two distinct parts of the C92 just before reaching the edge of Coleraine, after which the road becomes more rural as it runs along the eastern banks of the River Bann. Eventually the road comes to a TOTSO with the second section of the C92 continuing straight on, with the C91 turning off to the south. Just west of the village of Balnamore, the route splits at a T junction. The route which heads east passes through Balnamore and continues to Ballymoney, approaching the town along Charlotte Street after crossing the Belfast - Derry line at a level crossing. Charlotte Street soon reaches a crossroads with the southbound-only High Street and Main Street both forming part of the C91 between the B62 and the B66. Back at the T junction west of Balnamore, the route heading south crosses the Ballymoney River and meets the B66 at a T junction. Just east of this junction the road continues south once more, soon passing the western end of the C89 as it does so. After a bit of meandering alongside the River Bann, the road straightens as it comes to an end on the B70 at Mclaughlins Corner.