I have increasingly come round to the point of view that building extra road infrastructure (especially motorways) just increases road usage (the old "build it and they will come") as people then think that they can live further away and commute.
The exceptions are safety and very obvious road arteries.
So, for example, the route between Glasgow and Edinburgh - which, believe it or not was only fully turned to motorway in 2017, with the "missing link" of the M8
- made absolute sense economically and on safety grounds (given the accidents due to the lack of a hard shoulder).
Ditto with some bypasses, to stop heavy traffic going through the centre of towns and villages.
But more needs to be done at the design stage to discourage very short trips on them.
And it should be done alongside upgrades in public transport. And to stop making it cheaper to go by car (even just petrol costs - as most people see the cost of the car as a "sunk" cost so don't take depreciation into account) even if there is only one person in the car 
But that would require an integrated transport strategy 