Autonomous Vehicles and Human Factors

Over in VC-land, we are told that autonomy will change traffic in cities from circuit switched to packet switched and from TDMA to CDMA. We will take this to mean that (a) riders may use several vehicles over the course of a trip and (b) several riders and several uses (passenger, freight) may use a vehicle for portions of a trip as the vehicle travels between two points. The alternative interpretation, that different portions of vehicles will be sent via different routes and different vehicles will simultaneously occupy the same space on the road, would be a bit too fantastical.

Astute readers have no doubt noted that we already have packet-switched CDMA transportation in cities: fixed-route transit service, where people board and alight at many points along the vehicle’s route, and users may be forced to transfer one or more times between different vehicles to reach their destination.

Looking past the annoyance of everything being turned into tech jargon, this is worrying because it is nothing more than a tech industry reframing of the mistaken “water through a pipe” philosophy of early traffic engineers. The idea that human users can be routed through a transportation network like packets of data across a communications network is akin to the idea that drivers move through a transportation network like water through a pipe. Understanding the human factor is one of the hardest learned lessons of traffic engineering, indeed, something many engineers still struggle to do.

People do not act like water in a pipe or packets of information on a network. Transfer penalties are real and vary with the person, the weather, the trip purpose, and other factors. Many people are not willing to share a ride with one anonymous person – note that the practice of “slugging” arose where HOV restrictions required three people rather than just two.

It is also not certain that ride sharing will replace single occupancy vehicles as autonomous vehicles become more prevalent. None other than Randal O’Toole provides some reasons why: people like having their own car with their own stuff in it, people don’t like the idea of a stranger using their personal property, and if autonomous vehicles reduce the cost and annoyance of car ownership, more people may choose to own. You’d be crazy to pay to keep a car in Manhattan & drive it around, but what if you could have the car drive you around and then go park itself in New Jersey when you don’t need it?

Another example of ignoring human factors is some presentations of automated intersections. For this to work, if pedestrians and bikes are to be permitted at all, they would have to behave in a perfectly predictable manner. Of course, we don’t – we stop to take out our phones, we stop to look at things, bike chains slip off gears. If full automation and vehicle-to-infrastructure communication are achieved, these intersections could prove useful for junctions of limited access facilities, but they won’t be popping up in cities. (And they will likely be more conservative than presented in these simulations, due to the need to allow for mechanical failures, unexpected pavement conditions, and so on, but that’s another issue.)

I don’t mean to suggest that autonomous cars won’t have any impact on cities. The improvements to safety alone from eliminating human error, inattention, and bad behavior will be well worth it. But if you’re waiting for the paradigm shift of changes being hyped in some of the press, I wouldn’t hold my breath.


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