Steve Dombek is an activist with an unusual cause. He wants US cities in general — and San Francisco in particular — to adopt narrower streets, along the lines of what you'll often see in cities that were built before the 19th century.

Retrofit one block of San Francisco sidewalks into Euro-style narrow streets = space for 45,000 sq ft of new housing pic.twitter.com/hRa4aKSa4n — Steve Dombek (@SteveDombek) May 1, 2015

His point is that doing so could open up lots of space for the creation of much-needed additional housing in places like San Francisco, where thriving local economies are being strangled by an inability for more people to be able to move to the city.

Narrower streets could create tons of new housing

Right now, the public right of way on a typical San Francisco residential street like McAllister is 68 feet and 9 inches, enough room for 30 feet worth of pedestrian space and then almost 40 additional feet dedicated to automobiles.

That's great if you're an incumbent San Francisco homeowner who also owns a car and who is interested in storing and driving that car without fully bearing the costs associated with taking up scarce urban space.

But in a city like San Francisco where housing is very scarce and expensive, shouldn't some of that space be reused for something more valuable? Like people?

In the revised version of the street, you can still drive a car, but you'll have to do it slowly in a space that's shared respectfully with pedestrians rather than optimized for high-speed cruising. And there's no space dedicated to parking. That's not to say that nobody can park a vehicle. But to do so you're going to have to pay for parking in the private market, the same as someone looking for a place to sleep is going to have to pay for space. The government isn't going to create special zones set aside for vehicle storage.

What you gain is thousands of feet of new square footage for housing.

A good idea that's unlikely to happen

Dombek's idea has a lot of merit. Conventional urban policies set aside too much land for cars and not enough land for houses. That gives many cities a perverse mix of ubiquitous cheap parking and extremely expensive housing. Shifting the balance — especially in places like San Francisco — makes sense.

But the politics of this idea are very challenging. The problem is that it takes something (parking, specifically) away from people who already live on McAllister Street in order to benefit hypothetical occupants of new homes who, by definition, don't live there. That would be good for San Francisco, good for California, good for America, and good for the world. But it's not good for the people currently living on the block — and those are the people the city council is going to respond to.