Automated vehicles, transit, and physical space

Let’s put the brakes on this one before it gets driven out of control: driverless cars are not the panacea for traffic woes as imagined by some technologists and futurists.

I agree with public transit consultant Jarrett Walker’s assertion that a “completely imagined future” of driverless vehicles is neither realistic nor desirable, given that there will be problems in the intermediary stages, such as how driverless vehicles and human-driven vehicles will appropriately interact with each other, and who will hold legal liability in the event of collisions. However, I am surprised that Walker did not argue the “geometry” angle for why mass adoption of driverless vehicles (particularly Personal Rapid Transit) is untenable – this is one of his significant themes.

In the series on which Walker’s post is based, author Richard Gilbert argues that

Travelling in an AT [autonomous taxicab] will be incomparably better than travelling by bus or even streetcar. As a consequence, ATs will replace much transit as we know it.

No, they won’t. There is the simple issue of the amount of space personal vehicles occupy on the road compared to transit vehicles, whether driven by a human or a computer. Technology, though wonderful, cannot overcome such a physical limitation.

A typical single-occupancy vehicle occupies far more space than a bus, streetcar or train. Even accounting for carpooling (which is not common in North America), public transit vehicles make far more effective use of limited road space than automobiles, reducing congestion and gridlock. While driverless, automated cars are no doubt more spatially efficient than human-driven vehicles and (four times as much, according to Gilbert) and require less space for parking, they still fall well short of the number of people that can be moved in a given physical space using public transit. The alternative, in car-dominated cities, is gridlock, visible and well-documented.

In his defence, Gilbert concedes that heavy rail transit, such as subways and commuter rail, will still be necessary. Transit will actually be necessary on most bus and train lines also, per the geometry issue above. However, driverless cars may be competitive in rural and suburban areas, which are only effectively traveled by car.

More jarring though, are Gilbert’s arguments about comfort and convenience. While “door to door” convenience may be necessary in the suburbs, medium and high-density areas can be very effectively served by public transit, easily reachable by nearly all pedestrians living nearby. There seems to be an underlying connotation of traditional public transit being for everyone else, given that our underlying individualism demands personal space, shielded from the sensory intrusions of strangers. What a sad comment on our post-modern society then.

I’ve used numerous public transit systems – Toronto’s (where Gilbert is based) is reasonably clean, comfortable, and efficient, though the best transit systems in other cities eclipse it. The same cannot always be said about taxis, which driverless cars are primed to compete with.


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