I'm not sure narrow roads in old cities are due to lack of planning, they didn't have crystal balls

And some of the "planning" that was done to make our cities car friendly was absolutely horrific - look at what someone thought was a good idea for Edinburgh:

https://www.gcat.org.uk/blog/?p=682

Edit: thankfully never built!

See Glascow's M8 which did get built!

Narrow roads are not only found in old cities... They are everywhere.

But still for historical reasons, towns, villages, country lanes have been around far longer than cars

When most roads/streets are narrow it makes it acceptable to plan new ones narrow too. I live in a neighbourhood built in a green (farm) field in 1990s - residential street are wide enough for two compact cars to pass each other but nowadays half of the street used for parking (for lack of better places).

Narrow roads should be a sign of planning. They do a far better job of restricting vehicle speeds than a nice wide open straight road with a 25mph (or equivalent) speed limit sign. My US city would benefit from far more narrow roads. But even the “quaint and quiet” residential streets are so wide that cars feel comfortable flying through at double the speed limit. And I’m not talking about the occasional reckless driver. This is how the standard traffic flows because they have so much space and open sight lines. We have nothing in the way of traffic calming for pedestrian interactions. Posted speed limits are the only mechanism used to designate road speed. It doesn’t work.

All the more reason to reduce the number of cars on the road: prioritize active and public transport (so that people choose to use them where possible instead of driving a wasteful private vehicle).

Other measures should also be considered but our Tory government will never contemplate them.