Belltown P-Patch, photo by studio-d

No, I’m not drunk blogging or April Fool’s day blogging or anything. I have a point! Stick with me.

Many people say the way to solve congestion is to build more roads. I assure you this is not the case, and I can try to illustrate it by comparing roads to p-patches. If you aren’t familiar with them, p-patches are little neighborhood community gardens, where gardeners can rent a plot of land on an annual basis for a small fee and grow crops or flowers or whatever they like. There are dozens of sites spread across the city currently, and the fees for the gardens are fairly low, between $34 and $67 per year for between 100 and 400 square feet of gardening space.

A lot of people want to use P-Patches, but the supply is fairly low. The fee is far below the “market clearing” price for that amount of gardening space: the price would need to be much higher for the number of people willing to pay the fee to be equal to the amount of p-patch places available. Because of this, the wait for p-patches can be several years, especially in dense neighborhoods like Belltown or Capitol Hill. If a private business or individual were running p-patches, the price of a plot of land might be several hundred or even thousand dollars per year (rent for a 400 sq ft apartment is several hundred dollars a month), or there might be strict restrictions on what sort of gardening can be done by whom. A quick glance at the community gardens available in San Francisco shows that private gardens have often short waiting lists but very high fees ($3000 a year), have strict residency requirements (you must live in Alice Griffith Housing Development), or other restrictions. San Francisco’s public gardens generally have extraordinary wait times (2-3 years) or are located far away from population centers (Fort Mason). Basically, if something’s price is much lower than the demand, there are still ways to make you pay, in the case of Seattle’s p-patches you pay with your time.

Roads work much the same way. The SR 520 bridge is free to drive across, but a lot of people would like to drive across it at 8 in the morning. Because the supply of road capacity is lower than the demand for the road capacity, commuters are made to pay with their time to drive across the bridge. Now, you could decide to add more bridge-lanes, much like you’d want to add more P-Patches. But often if you add a new p-patch, new people might decide they want one. There are no patches at all on First Hill; if you put a p-patch there, some people living in that neighborhood would likely decide they want to use it. If you put a new patch next to an existing one in another neighborhood, new people would want to use it, possibly because they think the new waits are shorter or because they are shorter (‘I might not live here in three years, but I will live here next year’) and possibly just because it’s there. This is called “induced demand”. If you built a new bridge across Lake Washington, new people would drive across it in addition to the people driving cross the existing 520 bridge. Partly because wait times seem or are in fact lower, and partly because now you can’t live where you want to or work where you want to (‘I’d never have taken that job at the UW but now there’s an easy way to get there from Juanita so…’). You’d really need a lot of p-patches before wait times went away, maybe several times what is currently available. Similarly you’d need a lot of highway capacity before you’d have no congestion on the bridge, at least several times what is currently there.

There are, of course, obvious differences between p-patches and roads. You need transportation of some sort to get to work and make money. You don’t need p-patches at all, really. Few people move to be near p-patches, but a lot of people might move to be near transportation options. But ultimately, the two are alike in the fact that neither has a price that matches what people are actually willing to pay, and so users are charged with their time. Also, there’s no money to expand either enough to make wait times go away by increasing supply. And so we wait.