The A4640 starts at Castle Farm Interchange, which is M54 junction 4, and heads northwards, passing the reservoir that is located off the northwestern corner of the junction. The proximity of this lake means that both the area of the junction and the A4640 suffer from more low-lying fog than is usual for the area.
The route then heads uphill through the edge of Priorslee, before meeting the A5 at Limekiln Bank Roundabout, which also marks the top of the hill. This is just a simple roundabout junction, after which the route drops back down, meeting another roundabout that was constructed in 2008 to allow for access to a currently unconstructed housing estate. Only northbound traffic must use the roundabout, whilst southbound traffic has a lane that avoids the roundabout on the original line of the road at this point.
Dropping further downhill, there is a grade-separated junction that allows for access to another housing estate before we meet the B4373 at yet another large roundabout.
Along the next stretch, there are several half-completed stub junctions that were constructed to allow for access to never-built New Town housing estates. These stubs include (unlit) street lighting and paint, though access to them is prevented by earth banks.
Finally, the route re-enters the urban area between Donnington and Muxton, terminating at the Clock Tower Roundabout, where it meets the A518 which leads towards Newport and Stafford beyond.
Half-patched sign showing former number
What today is the A4640 was planned as one of Telford's Secondary Distributor network, which were to be dual-carriageways whose junctions were to be mostly flat roundabouts. This legacy has meant that the A4640 has wide side reservations to enable widening to the planned dual carriageways, and also the vast majority of the bridges on the route are sufficiently wide to allow for that dualling.
The route was originally numbered B5060, and was renumbered in 2008.