The Chiltern Main Line railway bridge over the A4421 Bicester bypass
The A4421 is a short road in Oxfordshire. It partly follows the former route of the A421 before that road was rerouted onto what had been the B4031 to reach the A43.
The route starts, at a roundabout junction with the A41, as the Bicester eastern bypass and runs along a brief section of dual carriageway, before dropping to single. The bypass has several different names along this section. After a couple of roundabouts near Launton, the road turns right close to Bicester Airfield – with the bypass continuing as the A4095 – and picks up the original A421 alignment.
The A4421 then follows the line of the Oxford – Towcester Roman road and has a speed limit of 50 mph. It passes through the hamlet of Newton Morrell and the village of Newton Purcell where the limit falls to 40 mph.
The route ends at a roundabout on the Finmere bypass near the old aerodrome, where it meets the current line of the A421.