Do people commute into Paris by car in relatively large numbers? Where on earth do they park?
Certainly in the UK cities I've known people who live in the core are much less likely to own cars, but people from outside rarely commute in by car to the core because it's just too slow.
Medieval city plans just don't suit cars, even where the walls were demolished to make a ring road. I used to joke that there was no way to fix Cambridge's traffic problem without demolishing a college, then someone showed me a 1960s plan that involved taking a corner off St John's.
> someone showed me a 1960s plan that involved taking a corner off St John's.
That's to be expected if you get someone from Trinity to draw up the plan!
Cambridge is becoming an incredibly hostile place to get to and around in if you don't live in the city. Partly it's a function of the population growth, but it is pushing people like me to spend more in towns like Bury St Edmunds rather than deal with Cambridge.
Paris is a bit special, it's not a city which kept a lot of its medieval layout heritage thanks to Napoleon III and Hausmann. You have a lot of Boulevard which are quite large and decently arranged.
As for commuting, it depends also. Basically, the subway is exceptionally dense within Paris (keep in mind that Paris, as an administrative entity is actually very small and dense, roughly 10km in diameter, and you have a station every 500 meters or so in any direction within it).
As for the Paris area, the regional trains (RER) are roughly in a star pattern, with the crossing point between the lines in the center of Paris (Chatelet).
All that means that if you live withing Paris, you can easily go anywhere in Paris, but also in most of the Paris area in roughly 1 hour max.
If you are in the suburbs and work within Paris, it's pretty much the same.
However, if you are in the suburbs, and work in the suburbs, then, it tends to suck, because if you are unlucky, you have to go from your home "suburb" to Paris and then from Paris to your "work" suburb which can be a huge detour.
As an example, I used to live southeast of Paris (Evry), and work in the southwest of Paris (Clamart), in that configuration using a car was the only viable option, and the few times I didn't have my car, taking the transports meant 4 to 5 hours commuting every day. Typically, I drove around 25000km per year in these years.
Then I moved within Paris, and my car became far less useful, I went for 25000km a year to 3000km a year because the public transports became a viable option.
And lately my job got closer to Paris, so I finally sold my car without replacing it.
As for traffic, the roads are not that bad, and there are quite a lot of rings/partial rings, (Peripherique near Paris, in place of the old city walls from the XIXth century, A86 about 10/15km from the center, and the A104/n104/n118 20/30km away from the center, and quite a few highways radiating from the Peripherique (A13, A6, A1, etc). But it's not enough and there are a lot of traffic jams. As an example, the 40km commute when I lived in the suburbs was taking me ~30 minutes without traffic jams, but typically it was taking me ~1 hour and in some cases, with an accident for example, even 2 hours.
Also, a lot of people tend to live in the east of Paris, where housing is a bit cheaper (like almost every European city in fact, the dominant winds pushing smokes and bad smells west to east). But you have more activities in the West, the biggest being La Defense (business district just west of Paris). Which means a lot of long commutes for these people.
So it really depends on your situation.
On last point that is interesting to note: I grew-up outside of Paris, passing your driving license between 18 and 20 years old is considered normal in such cases. When I started studying in Paris, I was a bit surprised to learn that a good portion of the students native from Paris don't even learn how to drive, or do so much, much, much later.
It seems like it should theoretically be viable to add some commuter rail lines following the same rings as the current peripherical roads, and improve the suburb-to-suburb transit experience.
Certainly in the UK cities I've known people who live in the core are much less likely to own cars, but people from outside rarely commute in by car to the core because it's just too slow.
Medieval city plans just don't suit cars, even where the walls were demolished to make a ring road. I used to joke that there was no way to fix Cambridge's traffic problem without demolishing a college, then someone showed me a 1960s plan that involved taking a corner off St John's.