The road measures 44.07 miles long and would take a car obeying speed limits 52 minutes to travel its length.
The A421 is a A Road and is located in the Zone 4 Highways Region.
This is a true long-distance route, journeying through numerous towns like Evenley, Finmere, Tingewick, BUCKINGHAM, Bourton, Thornborough, Singleborough, Great Horwood, Little Horwood, Whaddon, Snelshall West, Tattenhoe, Emerson Valley, Furzton, Bletchley, Redmoor, Beanhill, Coffee Hall, Eaglestone, Netherfield, Peartree Bridge, Tinkers Bridge, Woughton Park, Woughton On The Green, Monkston Park, Monkston, Kents Hill, Kingston, Brinklow, Wavendon, Glebe Farm, Magna Park, Eagle Farm South, Hulcote, Brogborough, Marston Moretaine, Wootton, Kempston Hardwick, Kempston, Elstow, BEDFORD, Harrowden, Cardington, Renhold, Roxton, and Chawston.
The road passes through several counties, including Northamptonshire, Oxfordshire, Buckinghamshire, and Bedfordshire.