|Length:||2.4 miles (3.9 km)|
|Now part of:||A40|
|Route outline (key)|
Originally the A40 ran on the left bank of the River Towy, running south of Llandovery through Llangadog. The A482 ran along the right bank to Llanwrda where it turned right at its current starting point and the A4080 began. The road headed downstream for a couple of miles, passing no places of importance and with hardly a road junction on its route. Presently it reached Ashfield where the A40 came in from the east and the A4080 ended.
In 1935 the road was renumbered as part of an extension of the A483, freeing up the A4080 number for use elsewhere. Then after World War II the A40 was given its current route, taking on the whole of the ex-A4080.