Self-driving cars might be "a coming congestion disaster"

In most of TreeHugger's discussions about the future of our cities in the era of the self-driving car, I have taken the position that "The autonomous car will likely be shared, smaller, lighter, slower, and there will likely be about a tenth as many of them." That's because our current cars are parked 90 percent of the time, which is unnecessary with a self-driving car, it can just to serve someone else. However transit expert Jarrett Walker sees the opposite happening in his post Self-Driving Cars: A Coming Congestion Disaster?

He doesn't think they will necessarily be shared, because "The ownership model is closer to the status quo, and the status quo always has enormous power." He also thinks that these cars will be very busy indeed, and will not just be sitting around parked 90 percent of the time like our current cars are. He describes a nightmare scenario posited by the University of Washington's Mark Hollenbeck:

A suburban father rides his driverless car to work, maybe dropping his daughter off a at school. But rather than park the car downtown, he simply tells it to drive back home to his house in the suburbs. During the day, it runs some other errands for his family. At 3 pm, it goes to the school to bring his daughter home or chauffeur her to after-school activities. Then it's time for it to drive back into the city to pick up Dad from work. But then, on a lark, Dad decides to go shopping at a downtown department store after work, so he tells his car to just circle the block for an hour while he shops, before finally hailing it to go home.

And of course this is perfectly logical- why pay for downtown parking when you can just send the car home- meaning there are twice as many trips.

miles traveled© KPMG

Walker also mentions a KPMG report that predicts that a lot more people might be on the road, including the older ones who otherwise might have given up the keys, or the younger ones who cannot yet drive. The numbers are huge; According to KPMG:

These increases in personal miles traveled (PMT) can ripple into even larger fluctuations in vehicle miles traveled (VMT) as vehicle occupancy rates change. For example, if more people started to select new self-driving options in the future—then we could see twice as much demand. And if we moved into a scenario occupancy rates fell below one person per car—for example, many self-driving cars without passengers—then the increase could be a staggering three to four trillion additional miles by 2050.

Unfortunately, Walker makes total sense here, calling this "really easy and obvious behavior for a driverless car owner," especially when roads are essentially free, why would anyone pay for parking? Why own two cars when you can send one back and forth to get the kids?

self-driving carTom Vanderbilt/via

I used to think that the self-driving car might make our cities better and greener. Then Allison Arieff convinced me that they will lead to massive urban sprawl: "If you can read your iPad, enjoy a cocktail or play a video game while commuting, time spent in the car becomes leisure time, something desirable." Now Jarrett Walker points out that they won't lead to wide empty open roads but will actually increase congestion. Time to get back on the bike.

Tags: Cities | Self-driving car | Urban Life

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