Bignell's Corner is a large three-level roundabout interchange providing full access between the M25, A1(M), A1081, South Mimms services and local roads. It is junction 1 of the A1(M), and junction 23 of the M25. The A1(M) passes underneath the roundabout in a north-south direction at the lowest level, with the M25 passing over the roundabout at the highest level in an east-west direction. The junction marks the point where the A1 heading north out of