The B640 was formerly the A606 through Oakham, prior to the completion of the town's bypass.
The road leaves the bypass at a roundabout at its eastern end and heads west along Stamford Road, winding its way towards the centre of town. It meets Catmos Street at a mini-roundabout opposite the Rutland Council offices, where it turns right and continues along the High Street. At Melton Road, it crosses the Peterborough - Leicester railway line at a level crossing next to the famous Oakham Signal Box; this is still a major bottleneck on the road. The B640 bears right on to Barleythorpe Road and continues on towards the village of Langham, ending at a roundabout back on the A606 less than half a mile before reaching the village.