This section of the M1 broadly follows the route of the A5 north-west. It started at the Watford Bypass (A41), which runs south-east to meet the A1 at Apex corner, and ended on the A5 at Crick. The M10 spur motorway connected the M1 to the North Orbital Road (A405/A414, a precursor of the M25) where it also met the A5 (now renumbered here as the A5183) and, to the east via the A414, the A6, which subsequently became part of the M25.