San Francisco is the second-densest large city in the United States (after NYC). It is denser than the Tokyo Metropolis (which, note, is not the Tokyo Metropolitan Area, which is less dense yet).
(NYC density: 10,831 people/km^2. SF density: 7,152 people/km^2. Tokyo density: 6,200 people/km^2)
Adding enough additional units to the city to make major changes to its affordability is not just a quick change to zoning laws. It's not just that there are height restrictions. If you made a quick change to height restrictions, you'd still find high density projects are expensive to build and prone to being blocked by the various other obstacles to building that a high-regulation city like SF has. And also, creating and funding big building projects takes time -- and there's a lot of pent-up demand for SF.
AND, if you did add tens of thousands of new dwelling units in SF in the traditionally less-dense areas of the city, you'd totally overwhelm the already struggling transport infrastructure of the city in those areas (and I have no idea about other infrastructure. Could the sewers handle this?).
Should we still lower the restrictions on infill development in SF? Yes. The restrictions are well past the reasonable. Will that in a short period of time make a major change to the affordability of the city? Not unless you hand-wave away the entire reality of SF.
Population density in "Tokyo" is much higher than you describe at 15k/km2 on average with many wards of 300-500k persons that are OVER 20k/km2. The Tokyo Metropolis includes Yokohama which is 30km away (it's like including all of Marin/San Mateo/Oakland), while the Met Area you describe would be like the whole Bay Area down to San Jose and halfway to Sacramento.
https://en.wikipedia.org/wiki/Special_wards_of_Tokyo
Seoul, HK, Beijing are similar and I think India has much higher densities still. Population densities in many parts of the world are much higher than SF. I could take a picture out of my window right now of a block of ~200x30story apartment blocks right next to each other standing like soldiers. It's not rare.
Do I want that for SF? No, but the density isn't that extreme... unless you're talking about total $ borrowing power of the individuals involved.
Tokyo's built-up area has population density near 150 (in persons/hectare, the SI unit of population density). It's nearly the same in the central wards and in the outer suburbs. Tokyo achieves that density with almost no one living in buildings over five stories high and the vast majority in free-standing single family homes under four stories.
San Francisco County, not including any suburbs, averages around 90, excluding big open spaces like the Presidio. The Bay Area is closer to 30, just in built-up areas, not including parks and open space.
Manhattan is about 500 and Paris 300.
Gp, of course, has fallen into the trap of including open space in his calculations. Most metro statistical aggregates include a lot of surrounding farmland, ocean, and parks and don't reflect density experienced by residents or development intensity on available land.
I agree... most of Tokyo is only ~3 stories high and it has quite a few parks... there are wards as dense as Manhattan, but only of a few 100k, and it has truly spectacular subways, like Paris, and Manhattan.
There are portions of Shanghai, Beijing, Seoul, HK, Shenzhen that are at incredible densities. Having 6 neighboring blocks of 20-30 30+ story apt buildings isn't rare. I don't now how many people live per floor, but 15-30 seems very reasonable (they aren't empty). Each block has it's own schools and police/fire supporting 10k people in an area the size of a city block with Malls on the lower floors. Those neighboring blocks (still much less than 1km sq) are close to 100k/km2!?
Yes, there seem to be a common misconception that it's density as such that matters. Successful big cities are not based on density, but the fact that they go on and on (making some areas very dense indeed), while San Francisco quite quickly becomes suburbs. Everyone always comes dragig with examples of cities that developed over decades. A more apt, but still unlikely, comparison would be something like Vancouver. Personally I think that the ship sailed when the tech companies built campuses instead of towers.
But in fact the financial district is not all of NYC. And there are plenty of places in SF that have higher than its overall average of 7,100/km^2.
The point is, the meme in HN is that San Francisco is some weird spread out suburb like, I don't know, Houston (1,414 people/km^2). It's not. It's already quite dense. Could it be denser? Obviously yes. Could it QUICKLY become SO MUCH denser that it radically changes the affordability of the city? Only in the fairy land where you ignore every part of reality that's inconvenient.
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.
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.
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... )
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.
(NYC density: 10,831 people/km^2. SF density: 7,152 people/km^2. Tokyo density: 6,200 people/km^2)
Adding enough additional units to the city to make major changes to its affordability is not just a quick change to zoning laws. It's not just that there are height restrictions. If you made a quick change to height restrictions, you'd still find high density projects are expensive to build and prone to being blocked by the various other obstacles to building that a high-regulation city like SF has. And also, creating and funding big building projects takes time -- and there's a lot of pent-up demand for SF.
AND, if you did add tens of thousands of new dwelling units in SF in the traditionally less-dense areas of the city, you'd totally overwhelm the already struggling transport infrastructure of the city in those areas (and I have no idea about other infrastructure. Could the sewers handle this?).
Should we still lower the restrictions on infill development in SF? Yes. The restrictions are well past the reasonable. Will that in a short period of time make a major change to the affordability of the city? Not unless you hand-wave away the entire reality of SF.