The first roundabout is the terminus point of the A1198, a Royston to Huntingdon road which is in a perfect straight line, and serves part of the London - Lincoln Roman Road, Ermine Street. This road was also previously numbered the A14. Ermine Street now joins the A1 and the A607 where it enters Lincoln. Unfortunately, the road is not all joined up, and there is very little trace south of Royston. The site of this Roundabout, or near Royston, may have been a junction for Ermine Street and Icknield Way. The previous dual carriageway may also be part of the ancient Icknield Way. If you were to continue along the A505 towards Cambridge, you would still be using the Icknield Way. The road may not just be Roman, with many fossils found along this path. After the Junction with the A1198, is a large cutting to form the A505, then is a roundabout with the A10, with northbound going to Cambridge via the popular SheprethWildlife Park and Trumpington Park and Ride. Southbound on the A10 will take you into Royston towards London. The A505 continues northbound, leaves Hertfordshire and enters Cambridgeshire. ;Cambridgeshire - Royston to A11 After the Sawston junction, the road continues forward and joins the A11 Northbound ONLY. The left lane is to access Cambridge, Haverhill and Linton on the A1307, and the right lane for A11 routes to Norwich and Thetford and A14 routes EAST to Newmarket, Bury St Edmunds, Ipswich and Felixstowe. After the A1307 to the Six Mile Bottom Junction is part of the Icknield Way continued from the Chesterfords and the A505 before.
Bypasses
For part of its route between Leighton Buzzard and Dunstable, the road uses the former route of the Leighton Buzzard to Luton railway, as far as Dunstable. It also shares its route with the A5 near Dunstable and the A1081 near Luton Airport. The section between Letchworth and Royston follows the Icknield Way, with the deviations of modern bypasses at Baldock and Royston. The £43 million Baldock bypass includes the Weston Hills Tunnel.
Earlier routes
Originally the route started in Dunstable and ended in Luton. The rest of the route was originally designated the A601 to the A11, but was extended west to Wing Hill, near Linslade, when the Leighton Buzzard bypass was built. However, the western Leighton Buzzard bypass has since been built and designated the A4146. As a result, the section from Billington Road to Wing Hill has also been designated the A4146.