[2] At the time, the M1's southern terminus was at junction 5 at Berrygrove, with the main route from there to the A1 in London being via the A41 Watford Bypass.

Since the capacity of the A roads was much less than that of the motorway, a distributing spur was required to split up the traffic and reduce congestion at Berrygrove.

The M10 was thus built to distribute southbound traffic on the M1[3] onto the A5 (now A5183) and, as an alternative, via the North Orbital Road and the A6 to the A1 Barnet Bypass.

[5] As traffic could now travel between Hemel Hempstead and Park Street Roundabout without having to access the M1, there was no need to keep the M10 as a motorway.

This also had the added bonus of allowing lorries to park when waiting for access to a proposed rail freight depot.