From “Marc“. Links added by me.
It seems that Jevons Paradox is always in force: as single-occupancy travel has become cheaper and easier over the centuries (first by foot, then by horse/carriage, then by bike, then by car/taxi, then perhaps by autonomous car), all we’ve done is induce more travel.
This is hardly “bad” – who wants to be stuck in the village they were born in for their whole life like most people were in the 18th century on the eve of the Industrial Revolution? – but I think it merely means we can’t yet argue that autonomous cars will overcome the timeless congestion-caused-by-induced-travel phenomenon, and that if congestion therefore remains in populated areas, so too will remain the pressure to get around it via fixed-route transit, on dedicated lanes, viaducts, and tunnels wherever possible.
All we’ve been doing in the great project called civilization is swapping out the mode of congestion – the old 1930s Garden City documentary “The City” showed sidewalks oppressively crammed with people, then with horses and carriages and bikes, then finally with cars. Ironically and against what we would ever have expected, the postwar trend towards dispersed settlements has only increased congestion exponentially – why do Atlanta and LA and Houston build 10-lane highways in a desperate effort to outrun congestion, only to find they have to widen them a couple years later?
Amazingly, dilution in living patterns induced by ever-cheaper/easier transportation has not led to congestion relief, but exacerbated it tremendously due to the ever-increasing need to travel for *more and more basic functions that previously required less or no travel.*
Why is there any reason to believe that autonomous cars will overcome this ancient dilemma? I can imagine a world where autonomous cars are eventually organized as efficient rideshares to minimize a lot of initial wasteful, capacity-gobbling deadheading and idle cruising, but I think when the initial wasteful excesses are wrung out, the resulting available capacity will be swallowed by increased travel induced by efficiency. Again, this is hardly “bad,” I think it merely means that we probably won’t escape congestion and therefore there will be perpetual pressure for space-efficient workarounds for congestion (transit).
Finally, while I can imagine eventual vehicular throughput gains on urban/suburban streets induced by cheap mass ridesharing (i.e. fewer single-occupancy vehicles, which will always be inherently space-inefficient regardless of who/what’s piloting them), I’m finding it hard to imagine increased throughput under the “faster and closer bumper-to-bumper travel” assumption. On most urban and suburban surface streets, bumper-to-bumper travel at low to moderate speeds is already the norm, so can we really push the cars closer together? If you’re already two feet behind the guy in front of you, can the autonomous vehicle get any closer? At such close distances, aren’t human reaction times irrelevant because physics are still in force: you’ll still need a minimum distance for a vehicle of a given weight to safely accelerate/decelerate/stop regardless of who/how it’s being piloted.
Moreover, low urban speeds are caused by the *basic structure of the urban fabric itself* – small blocks and frequent conflicts. Autonomous cars can overcome this if we enlarge blocks and limit conflicts (as we already do for limited-access highways) by introducing “smart intersections” and various other traffic control tactics that will attempt to allow strings of autonomous vehicles to speed unimpeded through urban and suburban blocks. But will it be a Pyrrhic victory like the first attempt was?
I love it when someone who can think historically wades into this debate. Commenter “MaxO” replied:
Here’s a good discussion of the potential for self-driving cars to reduce (or even eliminate) road congestion and increase road capacity: http://www.templetons.com/brad/robocars/congestion.html
I also think you’re misrepresenting Jevon’s Paradox. It doesn’t mean that if supply is increased, demand will always increase to consume all of that additional supply. If it did, all roads would always be at capacity. It just means that an increase in supply is likely to induce some increase in demand.
To which Marc replied:
Max, I like the author’s thorough musings, but I think he still seems to be falling exactly into the trap I described: He described various *efficiencies* that will only increase capacity, thereby inducing more travel to fill the capacity.
I’m not arguing that induced travel will cause us to hit capacity *everywhere*, but in any economically dynamic region any transportation efficiencies always seem to be gradually eaten away by induced travel. Autonomous vehicles might not overwhelm Boise or Cleveland – unless they become economic dynamos (again) – but they could Houston or LA.
None of the efficiencies the author described are novel – in fact, we’ve been undertaking most of the improvements he cited for centuries already – lighter and smaller cars, better traffic control devices with optimized timing, better parking management, and so on – and we’ll continue to do so. But again, in regions with dynamic economies, these efficiencies will free up capacity that will be eaten up by induced travel.
It *would* be possible to overcome the historical noose of congestion if the spatial efficiencies autonomous cars introduced unfolded extremely rapidly – in less than a decade. That is, the road space they’d free up would increase so quickly that it’d take us years to dilute ourselves further enough to fill up that road space.
However, as I’m sure the author would concede, these tremendous spatial efficiences – the “1000%” increase in road capacity he pondered or even something more modest like 100% – wouldn’t occur overnight, but over a period of decades. It takes a considerable amount of time for enough of the improvements he described to happen at large enough scales for us to see the capacity increases. It takes time to replace traffic lights on a large enough scale to see large-scale improvements, for enough people to progressively purchase lighter and lighter autonomous cars, for new maintenance and operational practices (“convoys” etc.) to replicate themselves at scales large enough to reap the purported capacity increases.
That is, I think that because these improvements and their resulting capacity increases will occur *gradually,* precisely because they’ll occur gradually any modest, gradual, incremental increases in capacity will be eaten away in tandem by modest, gradual, incremental increases in induced travel. Isn’t this already the history of road transportation: from, say, 1880 to 1980 didn’t we increase roadway capacity by many thousands of percent through incremental roadway construction/enlargement and gradual improvement in vehicular and traffic management technologies? Yet in regions with dynamic economies, incremental induced travel kept pace with incremental increases in capacity. Had that increased capacity caused by efficiency flooded those regions in, say, 5 or 10 years, then maybe we would have thought we “out-teched” congestion. But it always catches up with us – at least in any area where even modestly large groups of people congregate!
(Marc and MaxO, if you want to be linked to here, please contact me.)