While autonomous vehicle enthusiasts may be enamoured by rapidly evolving and exciting new technology, it is important to be reminded of the geometrical limitations of cars, limitations which cannot be overcome by technology. The image below illustrates this simply and clearly; cars operated by drivers, ride-sharing programs, and autonomous vehicles all take up the same amount of space as each other and can only hold so many occupants. The original photo was commissioned by Australia's Cycling Promotion Fund in 2013; this one has been modified to emphasize the space that cars take up. As transit consultant Jarret Walker writes, “technology never changes facts of geometry. However successful driverless cars become, transit will remain crucial for dense cities because cities are defined by a shortage of space per person. Mass transit, where densities are high enough to support it, is an immensely efficient use of space.”
Although autonomous vehicles could make driving safer by giving the freedom to passengers to occupy themselves with activities other than driving, they will not be efficient at moving massive amounts of people in urban spaces; they are simply limited by the space they take up. Anoush Darabi, contributor to the public servant peer-to-peer group Apolitical, writes, “driverless cars still face a critical challenge: capacity. Mass public transit is able to move far more people in any given time than individual cars, even when those operate in fleets. While cities’ buses or rails can move 10,000-20,000 people an hour, private motor vehicles move just 600-1600.”
In terms of efficiency, autonomous vehicles cannot compete with public transit in urban areas. On the other hand, there will arise a density that autonomous vehicles will do well in. Zak Accuardi, Senior Program Associate at TransitCenter, an urban mobility foundation based in New York City, posits; “In lower density settings, more suburban, more rural, I can imagine autonomous vehicles playing a bigger role, and certainly the safety benefits of driverless cars are the biggest promise.” With more and more of the global population moving to urban areas; from 30% in 1950 to 54% in 2015 as well as estimates up to 66% in the next 15-30 years (Bret Boyd, 2018), the feasibility of autonomous vehicles completely revolutionizing how we get around in urban areas is unlikely, while they will likely have a larger impact in suburban and rural areas.
In closing, I’ll end with a quote from Jarret Walker, whose clarity and eloquence in thinking and discussion are much needed a world full of technological hype. “When you drive alone (or take Uber alone) in a gridlocked street or freeway, you are taking more than your fair share of the limited space. When stuck in traffic, you are blocking others from moving freely. If cities want to move people faster than walking while allowing them to take up only their fair share of space, two options arise. One is to use a vehicle that’s not much bigger than the human body, such as bicycles and scooters. Those tools work well for certain people in particular circumstances, but not for everyone. The other option is to share the ride in a vehicle. If space is really scarce, that vehicle will have to carry lots of people. In most cases, riders will have to share a vehicle with strangers, people who are not traveling for the same purposes or even to the same places. That’s what public transit is.”