The A812, less than a mile and a half long, acts as a western bypass route for Dumbarton town centre, connecting the A814 to the A82.
Commencing at a junction with the A814 near to Dalreoch Station on the west side of Dumbarton, the A812 heads north as Renton Road, immediately crossing the railway line to Helensburgh. The road itself then follows the Alexandria branch line north through open countryside.
After about three quarters of a mile, a slip road from the westbound A82 joins from the right, and after passing under the trunk A82 itself the A812 reaches an end-on junction with the B857 which is the northward continuation of Renton Road. The road to the right at this point is a slip to and from the eastbound A82 (there is no access here to the westbound A82).
The original A812
The original route of the A812 is Bank Street (now mostly the B857) in Alexandria. In 1935 the A82 was rerouted via Alexandria, moving the A812 onto that road's vacated route south to Dumbarton. Further improvements to the A82 have truncated the A812 to its current route; the northern section into Alexandria is now numbered B857.
For more information on the history of the A812, see the A82/Great Western Road page, as the two routes have been inextricably linked.