Hill of Tara 40
Image by CianMcLiam
Hill of Tara

M3 go-ahead

"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.

The motorway will simply get two lanes of traffic to the N3/M50 junction a bit quicker so that two lanes of people will now have to sit and wait to get on to the M50 motorway at the terrible junction there, which won't be changing much from what I understand).