CC image from the Museum of American History.

To date, most of the writing about driverless cars seems to focus on technology’s potential to make driving safer by eliminating collisions between vehicles. The thinking is similar to other auto safety improvements such as air bags or anti-lock brakes. These technological advances (endorsed by the US DOT)  incrementally improve the safety of those driving – assuming that you are using a narrowly focused definition of ‘safety.’ However, an auto-centric definition of safety only works in auto-centric environments; in urban environments where cars and bikes and pedestrians are all sharing the same space, the definition of safety cannot solely focus on eliminating collisions between high-tech cars (more on this later).

Other articles predict that driverless cars mean the end of transit – an unlikely scenario that ignores the basic geometry of car-based systems and the capacity advantages of transit (imagine shutting down New York’s transit system and trying to fill that role with nothing but taxis – good luck). Furthermore, if driverless cars make vehicle automation easy, then it should also help drive down the costs for automating transit itself (among other potential uses) and unlock the benefits of automated transit.

Ownership:

The far more interesting scenario is one where autonomous vehicles completely upset the benefits of owning your own car. In the Atlantic Cities, Eric Jaffe questions the assumptions of car ownership in a world of driverless cars:

But we’re not so far away from this future that it’s too early to start considering what it might look like. As Matt Yglesias wrote at Slate in August, Google, the leaders in autonomous car technology, must have had some vision in mind to shell out $258 million for the car-slash-ridesharing service Uber: “ubiquitous taxis — summoned via smartphone or weird glasses — that are so cheap they make car ownership obsolete.”

Think about this world of shared autonomous vehicles for a moment. You wake up and get ready for work, and a few minutes before it’s time to leave you press a button and order an SAV [Shared Autonomous Vehicle]. The car has been strategically positioned to wait in high-demand areas, so you don’t have to wait long. You might share the ride with a couple travelers just as you share an elevator, or perhaps pay a premium to ride alone. Either way, you clear your inbox or read the paper during the commute, which is safer and more reliable than it used to be.

So, basically Robo-Uber. Or Auto-Car2go. Or Johnny Cab. This kind of behavior seems to be a far more likely outcome of the technology than the continued paradigm of each individual owning a car for personal use. Just as transit consultant Jarrett Walker talks about the importance of frequent transit service in providing freedom for users, the on-demand nature of the personal car is similarly freeing – but it required a) ownership of the car to ensure on-demand use, and b) the owner to actually do the driving.

Travel Behavior:

But what kind of changes in behavior can we expect from this shift away from car ownership? Writing at Greater Greater Washington, Nat Bottigheimer notes that planners haven’t even begun to address the issue. Jaffe’s article, however, cites some preliminary research from Austin on the impact of robotaxis.

Civil engineer Kara M. Kockelman of the University of Texas at Austin recently modeled the potential ownership change with grad student Daniel Fagnant…

The results offer an enticing glimpse of a world without car-ownership. Each SAV in the Austin model replaced about 11 conventional household vehicles. The roughly 20,000 people who made up this shared network, formerly owners of roughly as many cars, were now served by a mere 1,700 SAVs. Travelers waited an average of only 20 seconds for their ride to arrive, and you could literally count the number who waited more than 10 minutes on one hand (three). That’s to say nothing of personal savings in terms of cost (insurance, parking, gas) and time.

“Even when we doubled or quadrupled or halved or quartered that trip-making, we didn’t have big changes in our key variables,” says Kockelman. “This replacement rate, this eleven-to-one, those things were very stable.”

Kockelman is quick to point out the caveats. The biggest is that for all the savings in private car-ownership, vehicle-miles traveled doesn’t go down in the Austin model. In fact, it goes up about 10 percent. That’s because not only are SAVs making all the trips people used to make on their own, but they’re repositioning themselves in between trips to reduce wait times (see below). The additional wear also means manufacturers produce about the same number of cars, too, though each new fleet is no doubt a bit smaller and cleaner than the last.

So, a huge decrease in the total number of cars (presumably, with a corresponding decrease in parking demand, making the already-questionable logic behind zoning code parking requirements even more dubious) but an increase in the total vehicle miles traveled indicates that such technology won’t be a magic cure for congestion. It won’t spell the end of public transit in our cities. If the safety benefits accrue mostly to highway travel, it won’t change the need for safer streets where pedestrians, bikes, and cars mix.

The next question is on the impacts of driverless cars on cities and city planning.