"One day of course when the oil runs out (probably in the near future) the motorways will sit silent and neglected - another short term folly."

Dammit. That was going to be my punchline!
Next year, the world will produce it's maximum amount of oil. Thereafter, it'll fall forever, and any we do get will be progressively harder to produce so the price will rocket. The road will relieve congestion for a single generation, maximum.