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The coming robocar apocalypse

May 18, 2012

How will driverless cars affect the built environment? A lot of the discussion lately has focused on whether driverless cars will affect the demand for rail. Michael Lind thinks they will make rail obsolete. Alex Block, sensibly noting that a change in technology won’t change the relevant geometries, disagrees.

Matt Yglesias (responding to a Randal O’Toole post that has been taken down) foresees a parking bubble:

[R]ight now every metropolitan area in the United States contains many, many more parking spaces than automobiles. When you’re at work, the space allocated for your vehicle at home sits there empty. When you’re at home, the space allocated for your vehicle at the office sits empty. Malls build parking to accommodate demand during peak hours, and the spaces mostly sit empty off-peak. But if the cars could drive around without a human pilot, there’d be no need for such lavish supplies of vehicle storage. In principle, a metro area could get by with fewer than one parking space per car since even at minimum-demand times a nonzero quantity of vehicles would be in use. That’s probably extreme, but right now depending on how you count we have somewhere between three and eight parking spaces per car. If the cars don’t need to sit idly waiting for you until you want to leave (imagine a world of cheap, ubiquitous taxis) that number is going to become totally ridiculous. After exploding for about 60 years, the torrent of parking construction is going to halt very suddenly and then start shifting into reverse. That should even make some rail lines more useful. Commuter rail stations, for example, will no longer need to choose between park-and-ride and transit-oriented development models. Every station will be a little TOD neighborhood, and people from further away will get dropped off and picked up at the station without needing to worry about storing a car there.

I agree with Matt that if robocars become ubiquitous, then we will see a reduction in demand for parking. But we will not see a reduction in demand for vehicle storage.  Vehicles will continue to exist, to occupy space, whether someone is behind the wheel or not. Driverless cars will simply encourage a shift from static vehicle storage (a/k/a “parking lots”) to dynamic vehicle storage (a/k/a “streets”).

Donald Shoup has harped (pdf) on the phenomenon of “cruising for parking.” It is one of the hidden costs of underpriced street parking. Underpricing street parking causes every spot to be filled, which, in turn, causes drivers to circle the block, searching for an open spot or waiting for one to open up. Shoup surveyed a number of studies which found that, on average, 30 percent of the traffic flow consisted of drivers cruising for parking.  Underpriced parking, counterintitively, means congested streets.

There is a built-in check on cruising for parking, though: every driver eventually wants to stop and get out of the car. Drivers aren’t cruising for fun; they are cruising in the sunny hope of finding a place to store their vehicles and get on with their business. If a particular part of town gets a bad parking rep, then a lot of drivers won’t even bother going there. The fact that, today, drivers must tether themselves to their vehicles while in motion limits the amount of congestion from cruising.

With robocars, though, we’ll witness a new phenomenon: cruising in lieu of parking. Rather than cruise Congress Avenue for fifteen minutes looking for a spot so I can get a taco at Chipotle’s, I’ll simply have my car drop me off at the door and command it to spend the next 30 minutes getting in everyone else’s way while I eat. It’s a pretty simple cost-benefit calculation: add the cost of parking to the cost of the anticipated time it will take to find a parking spot; if that cost is higher than the cost of gasoline, then just order the car to cruise.

It won’t take a lot of people engaging in this practice to congest the streets. Just imagine, say, an extra 200 cars continuously cruising up and down Congress during the middle of the day. What’s worst is that the people who will benefit from the practice will incur none of the costs. On the contrary, the more gridlocked the traffic, the less gasoline their cruising cars will burn.

In fact, this perfectly rational practice will probably be so harmful, so patently selfish, so despised that it will be necessary to outlaw it. Which means everyone will still have to find a spot for his car, driverless or not. Which means that, despite the title of this post, we might not see a robocar apocalypse after all, or a parking bubble, either (other than the existing bubble that local governments have created with underpriced street parking and mandatory parking minimums.)

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