From the Port of Felixstowe the road heads west, bypassing Ipswich to the south via the Orwell Bridge and to Stowmarket, Bury St Edmunds, Newmarket and Cambridge where it meets the M11.
There are three at-grade junctions: with the B663 at Bythorn in Cambridgeshire (junction 15); at the Leighton Bromswold turn a few miles to the east (junction 17); and at the Dockspur Roundabout at the edge of Felixstowe (junction 60).