I live in a neighborhood south of 280 near a bart station. Historically, it was a middle income neighborhood, and it is zoned SFH. The houses almost all have a small front and back yard. The front setback for many of the houses is the length of a car, with a driveway in the middle and a small garden to each side. The ground floor was almost always originally an extended garage with perhaps a storage room.
I think you can see it all falling apart. The proximity of this neighborhood to the peninsula, downtown SF and south of market, and the location near Bart and several muni rail lines, along with the general housing crunch in SF, has simply rendered this land too valuable for SFH residences. SF is trying, and failing, to suppress the alternate use of this land that the market is increasingly demanding.
Now, I'm not arguing that land use regulations are inherently bad, and I believe that SF is bad at governing. But here's what's happened.
The bottom floor, what was once a garage and storage room, has almost always been converted to a ground floor apartment or flat. Some people have gone so far as to replace the garage door with a wall and a front door. With the garage space gone, people have paved over the front setbacks next to their driveway, in order to park three cars in front of the house. Although curb cuts are technically allowed only to access the driveway and garage, these residents do of course keep the curb cut as a reserved parking spot in front of their house.
I'm not sure what to make of it. But one thought I've had is that what we're seeing here is an attempt to convert an old SFH neighborhood in to multi unit dwellings, and it has actually been a bit of a disaster. Curb cuts are no longer used to provide access to a garage, but they do break street into small sections, all too small to legally park a car, so total parking is a wash (though it does provide residents with a reserved spot). The illegal but largely unenforced pave overs have led to higher volumes of water going into the combined storm and sewage system (an archaic but energy efficient gravity based system used in SF, possible because it's a hilly place), and the excess water, mixed with sewage, floods the lower level spots where the pipes bottleneck, severely damaging properties and subjecting residents to severe health and safety risks.
Fascinatingly, San Francisco remains very strict and expensive where it comes to permits, but there's a level of permit violation that SF seems to just not bother with. In other words, you can do an un-permitted remodel of your downstairs, add drains, pave over the soil filter, create a massive sewage flooding problem, and sf will do... nothing. But if you were to try to tear down a house and replace it with a properly engineered multi unit dwelling... are you kidding me? SF will charge you upwards of 20k inspection and permit fees just to remodel the downstairs within the existing footprint of the house, if you do it legally. Anything beyond that is a massive delay with massive fees, and in most places, converting to official Muti unit dwellings is a non-starter.
The result is lots of illegal in-laws, with dodgy electrical and plumbing, in an area that is likely to flood due to illegal pave overs. During one of the heavy rain episodes, someone's dog was electrocuted and died. Really, I'd give it even odds that someone is going to die from this situation before long.
When I look around, I see something that just isn't working anymore. And while I bought into a SFH neighborhood, I do see something deeply immoral about restricting development in an urban neighborhood with excellent public transportation options close to job centers, in a world where low income janitors and fast food workers engage in soul and family destroying commutes for hours from exurb sprawl. It's nearly inconceivable that a city that considers itself "green"[1] and environmentalist would consider this OK.
The one thing I disagree about is the notion that SFH owners are protecting an investment. Personally, I believe that while my house itself would lose value with relaxed building restrictions, the land would be worth a ton if it were legal to build a multi unit dwelling so close to the urban core and multiple public transportation lines. Nah, the SFH associations are fighting for something other than the optimization of their asset. I'm a lifelong San Franciscan in my late 40s, and I know these people. They have a powerful attachment to their neighborhood character, they never plan to leave, they are largely indifferent to the value of their house, and the want things to stay "the same". I just don't think that's possible. Things can either grow properly, or we can try to put it into a container that will eventually burst at the seams - and this is what I think I'm observing in my own neighborhood, a place that is trying to grow, in ways that are harmful but don't have to be, because we haven't allowed the kind of growth that could actually benefit the city instead.
[1] when I replaced my old single pane windows with energy efficient windows, I got a tax credit from, get this, the Bush administration. Ironically, that incentive was almost exactly the same dollar value of SF's permit fees to replace my windows. Gavin Newsome's "Green" San Francisco pretty much confiscated the environmental incentive to reduce greenhouse gases created by the Bush admin. I mean, wow.