Regardless of what the density numbers show (which I suspect depends much more on what we choose to define as "the city" than on any reality), anecdotally it's impossible to get around comfortably in SF without a car.

Being able to live without a car is the defining characteristic of a real city as opposed to a sprawled-out suburb, in my mind.

I do know people who live in SF without owning a car but they use a lot of Uber/Zipcar/other rentals/car sharing etc. (as well as cycling and using delivery services). Personally, in their position, I'd probably own a car.

That said, there are very few US cities where you could live without a car without it being a hassle, especially if you want to leave your core urban area on a regular basis.

New York.

Maybe New York is the only real world-class city in the US. It's not a hard argument to support...

I'm less convinced that world class city inherently means "not owning a car is the norm and isn't really a compromise." That seems to give a lot of weight to what's ultimately your personal preference.

But, yes, if that's the definition, only New York (Manhattan in particular) really qualifies in the US. You can get away with it in other US cities but it tends to depend on stage in life, income, specific situation with respect to job etc., recreational activities, and how much hassle you're willing to put up with.

That said, living in Manhattan is a very specific lifestyle choice that isn't for everyone. I like visiting it now and then but the summer I worked there was enough.

Can you name many other world-class cities where one needs a car to comfortably survive? I've been to many such as Hong Kong, Tokyo, Paris, and London, and most people don't own cars in any of those.

"There are 2.6m cars registered in London. 54 per cent of London households have at least one car." -- http://content.tfl.gov.uk/technical-note-12-how-many-cars-ar...

"Tokyo has the lowest number in the nation–0.46 cars per household" -- http://blogs.wsj.com/japanrealtime/2014/08/18/number-of-cars...

I can't find cars per household for Paris, but cars per adult appears to be around 0.5, (https://halshs.archives-ouvertes.fr/hal-01069997/document), so cars per household can't be lower than that.

Hong Kong appears to be truly virtually carless.

Re: HK, not sure if this is cause or effect but the taxis there are much more plentiful and much cheaper than the US. The current conversion looks to be 10HKD = $1.29 USD. A 3-mile cab ride in HK is 60HKD, or about $7.74 ( http://www.numbeo.com/taxi-fare/city_result.jsp?country=Hong... )

In SF it's almost $12: http://yellowcabsf.com/service/cab-fares/

If we scale that to a 10-mile trip, assuming no waiting or traffic, which with SF is $33/hr extra, and in HK it's no charge (just by mileage) IIRC (having them wait is ~$12.38/hr):

SF: ~$31.05 HK: 150HKD=$19.35

This combined with their seriously great subway system ( https://en.m.wikipedia.org/wiki/MTR ) make it very practical to not own a car. You take the subway for short and medium trips, and hop in a cab at the end to get out to a relative's house in the middle of nowhere.

In much of Asia generally, income disparity is such that middle class-ish people can and do hire staff for a lot of things that they couldn't do to the same degree in the US or Western Europe. Thus things like taxis are cheaper.

And Hong Kong is relatively expensive. My experience in southeast Asia is that, in some places, you can hire a car and driver for the day for maybe $50 or so. So--combined with how horrible driving in the big cities there are--many people just have drivers.

Cities in general could be much denser. Those 7k people/km could be 27k people.

We know this because there are currently places that are 27k.

Those place in NYC that are 10k could ALSO be much more dense if the NIMBY didn't stop them from being so.

And yes, it could be done quickly. Just stop preventing developers from development. The market would LOVE to make tons of money by massively expanding.