The B5439 is a short link road in the Fylde town of Thornton. It was originally part of the A585 but gained its number when that road was moved onto its present route in 1979.
The road starts at a mini-roundabout on the B5412 not far west of that road's level crossing on the disused Fleetwood Branch Line. We head north along the residential Lawsons Road, with the railway line behind the houses on the right. After coming to within a stone's throw of the line the road bears off to the left and soon ends at a triangular junction on the B5268.