The M45 is a spur from the M1 in Northamptonshire, westward towards Coventry. Today it just provides access to part of Coventry from one direction on the M1, but its historical significance is much greater.
There's almost no evidence of Liverpool's 1960's plans for an inner ring road on the ground - but the motorway that never materialised would have been astonishing. The full details on the route, and the missing part the M62, are here.