Before the opening of the Plympton bypass in 1971, sections of today's B3416 were part of the main route of the A38 into Plymouth from the east.
The route leaves the present A38 at a parclo junction at Deep Lane, first heading north towards the industrial estates of Langage before turning left to descend the Glen Road valley, bypassing the north side of Plympton town centre.
From the site of the former Plympton railway station near the foot of Plympton Ridgeway the route continues along the former line of the A38 before meeting the western end of the Plympton bypass and the A374 at Marsh Mills. About 1 km of this latter part of the route is a D2/D2+3 formation with the carriageways running either side of the channelized Tory Brook.
