No - lots of major roads in urban areas have 30mph limits - see the map in post 26
Except, that is, for the reality of journeys on the ground - in which pretty much every single road in the capital city is now 20mph. This includes nearly 100% of the roads everyone actually uses to get anywhere including nearly all of those that would be described as "main roads" by anyone not being deliberately obtuse.
Most of the roads remaining at 30mph are a few arterial routes, many of which were until recently 40mph urban dual carriageways engineered as such for much of their length.
The parochial windbags at the assembly have also managed to recently reduce the main route out of Cardiff to... pretty much the rest of the world... from 70mph to 50mph for most its 17+ mile extent from Gabalfa interchange to the M4 beyond the eastern edge of Newport. That'll be the single most economically and practically important route in the entire nation then - but no problem, nothing to see here.
The petition raised via the official Senedd Petition route re the asinine indiscriminate 20mph idiocy has so far garnered getting on for 500,000 signatures - unprecedented by a gigantic margin. That's approximately 1/3rd of the entire adult population of the nation. At least in the earlier stages of this petition's progress, sampling by reputable journalists confirmed that the signatories are predominantly genuine members of the Welsh electorate.
At least in Bristol, which has also developed a fetish for 20mph restrictions, they are so far largely applied in a nuanced manner on roads where it is less obviously preposterous.
Much as it pains me to agree with a Westminster Tory, Penny Mordaunt had it exactly right in describing the use of a 20mph
default as "absolutely insane" other than in missing out the profanity that belongs between the two words provided.
"Welcome to Wales - We Are Closed for Business."