Motorway naming

[VB75]

The M6 was built before the M1. Why wasnt the first one built called M1, then M2 etc?

[New Judge]

Because, generally, they follow routes taken by the same numbered "A" road.

The M6 follows (roughly) the route of the A6, the M1 that of the A1, the M4 that of the A4 etc.

There are exceptions, but that's generally the idea.

[Clayhead]

Because the A1, A2, A3 etc. radiate from London in a clockwise manner and as the motorways were built to ease congestion on these roads they were named after these A-roads. Thus the M6 travels to the North-West, as does the A6..

[Androcles]

The first full Motorway was the M1, although the first motorway class road was the Preston Bypass which was incorporated into the M6, built before the M1

See: http://www.cbrd.co.uk/motorway/

[Clayhead]

Sorry, New Judge, we overlapped.