I would be hesitant to draw that correlation. IMO cars give you more access to third places, not less. With a car one can cover far more ground in a given 30 min drive after rush hour died down probably in every city in the world, than what one can cover in 30 mins walk and transit ride (especially when transit schedules might favor a commute into the central part of town vs some off peak trip to a random corner of town).

Say what you will about the ills of the car, but it takes a lot of specific context for them to emerge as the worst option of transport from an individual perspective. Really most of the cars ills are from their collective harms, something most can't appreciate as a tragedy of the commons sort of failing.

There's no shortage of third places in the American suburbs, you just have to drive to them. I'm sympathetic to the argument that walkable third places are better third places because I lived car-free in New York City for a decade and enjoyed many of them. But living in the suburbs or exurbs doesn't inherently mean you don't have access to shared communal spaces.

If I believed there is a crisis of isolation in the United States and degradation of community, I would first focus on more recent technologies, say ones introduced around 2007, than on technologies introduced in the early 1900s.

If anything, the golden age of third places coincided with the golden age of suburbanization, which was obviously heavily car dependent. Their death almost certainly has more to do with financialization making it harder for small businesses to stay afloat, a drop in demand due to competition for attention, and decreasing work-life balance eroding people's ability to socialize.

In my grandfather's day, one income was enough to support a household, and there was less free work being done on the job, which meant fewer hours and being less drained at the end of the day. And yes, people spent less time commuting, meaning they had more time and energy for socializing after work. But communities were also more decentralized, and population centers had fewer people in general. A big part of the problem is that modern cities can be massive, and invariably funnel people to a handful of work districts, which just doesn't scale. When you double the distance to the CBD, you quadruple the number of people coming in (give or take, it's not exact because we tend to increase density close to the CBD as a response to this). Take it from someone who's lived in a place where cars aren't really necessary, the logistics of urbanization are still a crap experience when you're crammed into a train carriage during rush hour. It's common for people to commute for 90 minutes on public transport in Asian megacities, for example.