The A918 appears to simply consist of the majority of South Street in St Andrews these days (with the A917 being the eastern end of the street). However that was not always the case. Until recently, the road appears to have had a spur which started on the A917 North Street as Greyfriars Garden, then Bell Street before reaching South Street. Changes to one-way systems seem to have removed the spur and just given the road its South Street route.
The original route of the A918
The old route of the A918, which always ran into St Andrews, is now part of the A917.
After running along South Street, the road left town along Abbey Street, following the present A917 as far as its sharp bend in Crail, which was originally the end of the A917 and A918.
By the 1980s the majority of the A918 was taken over as an extension of the A917, leaving behind the short section in St Andrews.