Most American streets are far too wide, which uses up valuable urban space, is dangerous for pedestrians, and actually makes traffic worse. That's why many cities are trying to hand over more street space to transit, biking and walking. But what if we took the lanes devoted to cars and turned it into housing? It sounds crazy, but this idea actually makes a lot of sense.
In a single tweet that was posted by Vox, Steve Dombek sketched out his very simple concept which uses his own San Francisco block as an example of how an extra-wide street (McAllister) could easily accommodate 4180 square metres of housing. The concept, called Narrow Streets SF, would put a row of housing down the center two lanes, leaving smaller streets on either side.
Dombek calls these two new roadways European-style streets, but to be honest they're not much different than the streets you'd seen in older cities like Boston or New York. The big difference, however, is the idea that these are shared streets (woonerf in Dutch), where cars, bikes, and walkers can all travel in the same area -- they just need to do it at slower speeds that make each mode aware of the others.
There are so many great examples of where this idea would work perfectly. Some cities are already implementing "road diets" to add bike lanes and wider footpaths, or closing streets completely to make public plazas -- in other words, we have the space. I can think of plenty of roadway candidates here in LA since so many of our streets were built extra-wide to accommodate our trolley system over a century ago.
This obviously would not be an option for every single wide street in a city, but maybe you could do an every-other-street model -- one for cars, one for housing. And there are plenty of things you'd need to make sure were already in place, like exceptional public transport so people would be able to ditch their cars (and parking spaces).
I have only one question: Why stop at three-storey apartments? The new generation of superskinny supertalls are only about 18m wide. I'm sure a 12m wide skyscraper would be possible. Now that would be adding some true urban density.