There are certain reasons cars are needed: goods transport and people with disabilities for example. I wonder if you could do a general ban with enough exceptions to be okay.
There's be a fraud problem though, and it could make it difficult for disabled people in practice (they may not be able to easily get the right badge, or be believed when they do, they wouldn't be able to benefit from car infrastructure…)
I'm really fond of the areas I've been where the only cars allowed on many streets are things like delivery and service vehicles.
I would expect that that kind of environment is actually a net improvement to accessibility for people with disabilities. It's probably quite annoying for people who use wheelchairs to get around a lot of places without a car, simply because the sidewalks are so frequently blocked off by people who've parked their cars across the sidewalk. There's one man in my neighborhood who frequently has to go out in the street to get around those sorts of obstructions, and is then stuck out in the middle of the road until he can get to the next wheelchair ramp in order to get back on the sidewalk. Limiting private car usage would admittedly only remove a portion of the sources of obstruction, but it would get rid of essentially all of the safety hazard that he has to take on in order to get around them.
And, especially now that cars are going electric and getting quieter and quieter, I would guess that restricting unnecessary car usage could be a big boon for blind people who want to be able to leave the house without a chaperone. I had one acquaintance who would essentially Uber everywhere - at great expense to herself - because she just didn't feel safe even trying to cross the street.
(Heck, I'm sighted, and sometimes _I_ don't feel safe trying to cross the street, especially later in the evening when a sizable portion of drivers are intoxicated and really are not watching for pedestrians.)
A lot of university campuses are like this. Very limited car access on certain roads, but maintenance etc. gets free reign to drive on the walkways even during heavy foot traffic.
That's a non-argument. You could say that about any regulation. I assume regulating transport for disabled people isn't that hard cause we already have system in place that deals with disabilities.
Even for disabled people cars are not a strict requirement. You could build a smaller vehicle that goes walking speed specifically for transporting the disabled & severely disabled.
Able bodied people in wheelchairs are the easy case - just pave the roads with enough smooth transitions.
Many cities in Europe have successfully banned cars in core downtown areas. You can adapt curbs, street crossings, and buses to work for people with disabilities.
In the U.S. priority parking is already given to people with disabilities, so the exception already exists and would just need to be extended. People using grandmas hangtag does happen but it's not all that common (and cities could always issue huge tickets for violators to deter bad behavior).
There's be a fraud problem though, and it could make it difficult for disabled people in practice (they may not be able to easily get the right badge, or be believed when they do, they wouldn't be able to benefit from car infrastructure…)