Chicken and egg. Subways enable density. Right now if you greatly increased the density of many SF neighborhoods, you'd overwhelm the transportation infrastructure. (Obviously there are neighborhoods with transit that could already support increased density).
Hilariously, I wrote my highschool senior thesis on this exact topic. It was a case study on Seattle, Houston, and New York and how density changed before/after transit was added. You can see the pattern pretty clearly, transit leads to density and not the other way around. Which makes sense, right? Because density can be increased one building at a time, but generally subways need a huge investment to put in an entire line at once and benefit from having an extensive network.
Is it really a Chicken and egg situation?
SF prices in the last years have skyrocketed, through out the city. The financial incentive to build is there. But there isn't massive building of new housing. That isn't because of the lack of subways. It's because of zoning laws and building regulations.
Thousands of new homes/condos are being built every year in SF, for the last few years. There is a massive amount of building going on, precisely because prices have skyrocketed.
However, more housing would be built, if the zoning laws and building regulations were less onerous.
I went to a private school. It was pretty non-traditional in many respects, and it wouldn't surprise me if writing a thesis wasn't common at other schools.
San Francisco[0] proper has a higher density than London[1], and slightly lower density than Paris[2] — two cities that have thriving subway + commuter rail systems.
I think you mixed up imperial and metric systems --- San Francisco has 18,451 people/sq mi. Paris has 55,000 people/sq mi. It's almost three times as much.
There's got to be a more useful metric than average city density; the 2010 US Census [0] places the 5 densest cities in the US as having a population under 70,000 (yes, I'm quoting Wikipedia). City planners must have a unit more like person-acres or something to get an idea of the actual spread of the density.
Standard density quotes for cities can be pretty misleading as it often reflects fairly arbitrary divisions. For example while Paris is indeed reasonably dense the oft quoted number is for a fairly small parcel of central Paris.
Moraga/Lafayette/Orinda is my favorite example of this in the Bay Area. I sympathize with the complaint that they aren't building enough, but I think the SFBARF/Lafayette lawsuit is stupid. Building more in those places wouldn't help us, because the transit capacity doesn't exist. Have you taken BART, or the Bay Bridge, or the Caldecott tunnel at rush hour? If 20,000 people move from the city to Lafayette, how do they get here for work?
But you can even find this in the city. Yeah, it'd be great to increase density in the Sunset. But have you actually commuted from the Sunset to downtown? It's a disaster. Muni is at capacity, and driving isn't an answer. You can cycle to work (I used to from 48th Ave), but that's a 7+ mile ride with a few hundred feet of elevation: it's not an easy casual ride for most people.
The idea that SF doesn't have the density to justify this stuff is... it's just not true.
San Francisco has a population density of 18,451/sq mi (7,124/km2)[1]. In the Unites States, That is denser than just about any place other than Manhattan. At peak times, busses are crowded and traffic sucks. Personally speaking as an SF resident, having more efficient public transit options would be awesome. I'll let others crunch the numbers of the feasibility of building & paying for it.
> In the Unites States, That is denser than just about any place other than Manhattan.
I think that depends on your definition of "just about." Every borough in NYC aside from Staten Island is much denser than San Francisco. Additionally, many parts of where I'm from – northern NJ – are even more so: Hoboken, West New York, Union City (the densest city in the country), Guttenberg (the densest township in the country), and more.
If you're talking about cities larger than a certain size, then perhaps, but even then, I personally think it's a bit misleading to single out just Manhattan.
It is not a matter of feasibility. Infrastructure transit produces tremendous returns in productivity. Even insanely overbudget projects like the Big Dig in Boston are already breaking even after only a decade, because of how much room for growth they produce.
This is why having fast rail, uncongested highways, and always expanding to meet demand are always worth the cost. Unless you can accurately forecast a downturn in regional economic growth irrespective of whether or not you meet transit demands, it is never rational from the perspective of long term city planning for maximum economic throughput to not grow the system and increase density.
Even as someone who lived on the periphery of Boston for much of the Big Dig, it's good that it was done--in spite of all the well-publicized problems. Of course, the fact that Tip O'Neill managed to funnel $10 billion or so of federal money to the city for the project doesn't hurt.
NYC has subways that extend out to less dense / borderline suburban neighborhoods. Though ridership to these terminals is much lower than in manhattan and northern brooklyn and queens, they're still an important way for some people to get to work.
I agree, however, that SF needs to build at a higher density (outside of FiDi and downtown) regardless of future subway infrastructure.
SF is the second highest density city in the US. I agree that as long as the NIMBYs prevent building housing, then SF won't really reap the benefits of improved transportation, but SF has pathetically bad public transport for the existing density. I live in much lower density Oakland/Berkeley, and I can get around by BART better than most city dwellers.
City-to-city comparisons suffer from all sorts of problems, not the least of which is that cities are defined according to their own historical, arbitrary borders that are practically meaningless when talking about actual issues.
Consider that NYC covers 302.6 sq/mi to SF's 46.69, which means that NYC isn't merely double the density, it's double the density over a much, much larger area.
This is why most serious comparisons are conducted at the level of the MSA (which would fold every one of the cities you're putting ahead of SF in density into a larger metro). Often, when laypeople compare cities, they're thinking about the MSA while quoting numbers they've found for cities-proper. That's why nobody in this conversation is thinking about Guttenberg, NY (and why mentioning it is almost a non sequitur).
I totally agree with you re: meaningless comparisons. However, I think the MSA comparison is pretty flawed as well.
For example, the Los Angeles metro area has a higher density than both NYC's and SF's (which is higher than NYC's), but it's obvious – to me at least – that in reality, considering only areas that most people would agree are remotely close to being in/near "the city," the density order of these three would be more like: 1) NYC 2) SF 3) LA.
But yeah, at the end of the day, I'm mostly being pedantic :)
Now guess which ones are central cities in their respective MSAs. Excluding those, guess which ones aren't part of the NYC or LA areas. Let's do ourselves a favor and exclude Poplar Hills, Kentucky (362). There's one city left, it's part of the Boston area (which is the next densest large city after SF), and you guessed it, Somerville has a subway with a separate light rail extension under construction. The only outlier is Sunny Isles Beach, FL (20,832), in the Miami area. And Miami? It's just after Philly, all known dense cities.
So yea, it's NYC, then SF, minus a couple pockets of LA. And these are all dense places that need subways. It takes a special sort of something to claim, as the top comment did, that SF is not dense enough to warrant a subway, let alone massive large-scale investment in all modes of mass transit as NYC has.
Hilariously, I wrote my highschool senior thesis on this exact topic. It was a case study on Seattle, Houston, and New York and how density changed before/after transit was added. You can see the pattern pretty clearly, transit leads to density and not the other way around. Which makes sense, right? Because density can be increased one building at a time, but generally subways need a huge investment to put in an entire line at once and benefit from having an extensive network.