The B931 is a short B-road along the Fife coast. Strangely, every classified road it meets is met in two separate places.
Wellesley Road, Buckhaven
The road starts on the A955 at a triangular junction on the northern edge of Buckhaven. The road heads south along Station Road to a roundabout where the B944 continues ahead into town whilst the B931 bears left along Wellesley Road. The other end of the B944 is met at the next roundabout.
The B931 continues northeastwards, a short distance inland from the coast. It passes the Fife Energy Park (an industrial estate plus) before crossing the B932 on the edge of Methil. It runs along the edge of town, still along Wellesley Road, before bending left then right to end at a roundabout, where both the B932 and A955 are met once more.
Methil in the 1950s showing the old route of the B931
The original route of the B931 had the same end points but actually followed what is now the A955 instead. The road from Buckhaven into Methil was the B927 (quickly upgraded to A955) whilst the section through Methil was unclassified.
This situation lasted until the 1960s when the A955 and B931 swapped numbers (although part of the old route of the A955 became the B932 instead), giving both roads their current routes.