Owing to the short length of the road determining its route accurately is difficult. However, judging from the map on the right, it appears to have started on the A2 Eglinton Street and headed northwest along Kerr Street. It presumably ended at the far end of Kerr Street, on Main Street which may have been the A29.
The B55 is not marked on any later maps although it is not known whether this is due to limitations of scale or whether the road no longer existed. What is certain is that the A29 now ends on the southern edge of Portrush and so the B55 is now definitely unclassified. Kerr Street is now one-way northbound.