"JNugent" writes:

(b) due to increases in traffic (especially during the prosperous 1980s),
the congestion would have been even worse had it not been for the
(relatively small) expansion of the high-quality road network (meaning that
not enough expansion has taken place).

Have you ever considered that building new roads might influence more
people to get into their cars? Many towns are now made up of large
segregated areas of industrial "parks", shopping "parks" and vast
residential suburbs without even a corner store within walking
distance. The only practical way to get between these places is to
drive. If the road network had not been expanded to accomodate such
"urban planning", a more sensible mix would have been found that did
not involve everyone driving everywhere.