1923 and all that
In order to see just how revolutionary the Northern and Western Motorway might have been, we need to look at the general transport situation in 1923.
The first Government attempt to create a central roads authority came in 1910, with the creation of the Road Board. The Board was funded from taxes on motor vehicles and on petrol, which was ringfenced for the purpose. However, the Board was relatively ineffective (though World War I hardly helped the situation), and in 1919 the Ministry of Transport was created, meaning that it was only four years old when the Northern and Western Motorway came along.
By 1923, the only road improvements that had been opened were a few small bypasses, with an improvement to the A2 Watling Street between Dartford and Strood being a notable exception. Even the first new-build inter-city highway, the A4123 Wolverhampton - Birmingham New Road (opened 1927) hadn't started construction, and the A580 Liverpool - East Lancashire Road (opened 1934) was just a line on a map.
Even road numbering itself was brand new, with the first allocations being in 1922; whilst Trunk Roads (those roads looked after by central government) would not be created until 1936. At this time, all roads were looked after by the relevant local authorities.
Railways, on the other hand, had just gone through the Railways Act 1921, which consolidated the previous companies into four companies, that split the country up between them. As a result, the railways were in a much stronger position than they would have been a few years earlier, and, of course, in these days when Dr. Beeching was still forty years away, the railways ruled the roost as far as long distance travel was concerned. If the motorway was to prosper, then it would have to attract traffic from the railways...
Outside Great Britain, the first motorways in Europe got the go-ahead in 1923 - the Italian Autostrade network; with the first construction near Milan starting in 1924.