A421 road
The A421 is an important road for east/west journeys across south central England. Together with the A428, the A43 and A34, it forms the route from Cambridge through Milton Keynes to Oxford. The section between the A1 near St Neots and the A5 in Milton Keynes is a national primary route.
Route
The road begins at the A1, just south of St Neots (and the junction with the A428 from Cambridge), at the Black Cat Roundabout. The road bypasses both Great Barford and Bedford to the south to reach the M1 at junction 13. From there, it swings up through the southern part of Milton Keynes, doubling as the local grid road H8 Standing Way. During this time it crosses the A5 (and connects to it via a short spur which is part of the V6 Grafton Street).
Continuing westwards as the route approaches Buckingham the road passes close by to the 14th century Thornborough Bridge, the only surviving mediaeval bridge in Buckinghamshire which was bypassed by the new bridge in 1974. Close to here, it then forms the Buckingham by-pass before joining the A43 (Northampton — M40 junction 10) near Brackley. (On crossing the A43, the route due westward becomes the B4031 through Croughton, Aynho and Deddington to join the A361 to Chipping Norton).
