Autonomous Cars and Induced Demand: a Historical Perspective (Comment of the Month)

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.

Congestion in Philadelphia, c. 1900. From, ironically, Professor Eric Morris’s article “How the Motor Car Saved the City, ”

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:

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.)

9 Responses to Autonomous Cars and Induced Demand: a Historical Perspective (Comment of the Month)

  1. Ian October 29, 2016 at 7:26 pm #

    Don’t get me wrong, I’m very skeptical of autonomous vehicles reducing congestion, and I understand the principles of induced demand.

    However, there must be a heretofore unseen upper limit on induced demand, right? If we’re talking about similar lifestyles to today’s (working, studying, sleeping, etc) then there’s only so much of the day’s time that can be taken up with traveling. Do we have some idea of what that is? Are the proponents of autonomous vehicles suggesting that we’ll hit that?

    • Henry October 29, 2016 at 10:04 pm #

      The data says roughly an hour of commute time each way, give or take. Assuming autonomous cars are supposed to speed traffic flow, maybe the sprawl of small and mid-size cities stretches out even further, but I believe it’s safe to say that in the sprawliest regions the process is over.

      Induced demand doesn’t necessarily have to take the form of sprawl, either. Since automated cars will be making parking lots useless in some versions of this future, all of a sudden there’s this underutilized real estate. Parking lots get redeveloped with much denser land uses, but not necessarily in walkable or transit-friendly fashion. Now you have a lot more travel demand to and from these places that may not be easily accessible by car, and you need transit to solve this problem since you got rid of all the parking lot frontage you could’ve expanded the roads onto.

      • el_slapper October 31, 2016 at 2:46 am #

        That’s an average, depending on the city. When I was in Paris(12M with suburbs), it was more than one hour for most of my colleagues. Now that I live in much smaller Montpellier(450k with suburbs), most colleagues are here in less than one hour. Be it by transit, bike, or car.

        Those cities seem to be better equipped in mass transit than most US cities, yet the global average seems to be one hour, here in France, too, to my experience. My cousins in Sao Paulo, don’t hope ever to find any job less than 90 minutes away from home. The more attractive the town is, the more people are ready to accept long commuting times, it seems. With the average of one hour you stated.

    • Mike Robinson October 30, 2016 at 8:18 am #

      In the UK, the average time spent travelling is about 360 hours per year or about an hour per day and it has remained at this figure for the 40 years since the National Travel Survey started.

      The miles travelled increased from 4,500 miles a year in the 1970s to peak at 7,000 miles per year in the mid 1990s and since then there has been a slight decline of this figure.

      The increase in miles travelled while the time spent travelling remained the same means that people travelled faster as a result of public transport improvements and increased car ownership.

  2. Neil Lewis October 30, 2016 at 4:30 am #

    I’ve thought for a long time that the whole idea of increasing transport capacity (whether personal or mass transport) is analagous to treating a symptom while ignoring the underlying problem.

    Congestion is primarily a result of commuting, not people’s desire to travel per she. People mainly commute to avoid living in areas of dense population, where most of the best jobs are located.

    Remove the desire or need to commute and congestion disappears.

    If anything like the sums spent on increasing the capacity of transport infrastructure were instead spent on encouraging remote working, there would be no need for new roads or railways. The existing infrastructure is more than sufficient for off peak needs.

    Of course remote working is not pracyical fir everyone, but for the majority of city jobs where the working day is mostly spent at a terminal, it should be applicable. It’s not even necessary for those jobs to be 100% remote. If 50% of commuters worked remotely 50% of the time, peak transport needs would drop 25% at a stroke. People could still have face to face meetings 2 or 3 days a week, but wotk and indeed meet virtually the rest of the time.

    The technology exists right now. It would reduce travel, pollution, stress, wasted time, costs. Why are we still putting billions into new roads and railways and complaining about their problems?

    • Eric October 31, 2016 at 5:38 am #

      This is much-discussed by people with more business experience than you or me. Managers are afraid that working remotely will lead to goofing off or being distracted by kids. Workers are afraid that they will miss out on the office camaraderie, the manager’s attention, and eventual better tasks and promotions. In many cases, there are no simple solutions to these problems.

  3. Kenny Easwaran October 31, 2016 at 7:52 am #

    Minor point, but is it really true, as Marc says, that “On most urban and suburban surface streets, bumper-to-bumper travel at low to moderate speeds is already the norm”? There are a moderate number of streets on which this is true at peak periods, but a smaller number of streets on which this is true outside of peak periods. But I doubt that there is any city in the United States where this is true on a majority of the streets, and very few streets where this is true for more than 12 hours a day. (Note that cars within a few feet of each other must be either stopped, or traveling at less than 10 mph or so.)

  4. Ming Iu November 1, 2016 at 1:01 pm #

    Oddly enough, the link that “MaxO” provides showing how robocars will reduce congestion, actually also says that robocars will increase congestion and we’ll need to use toll roads and congestion pricing to keep things under control. With autonomous cars, owners can send their cars to drive around without any passengers in them. The cars can be sent to park themselves, to drive around the block while waiting for the owner to go shopping, or to pick up things in other cities during the day, etc. Since owners won’t actually be in the cars, they won’t care about sending out their cars for errands in the middle of rush hour even if the cars have to sit around in traffic for multiple hours due to induced congestion.

    The current limitation on congestion is people’s tolerance for sitting in traffic for long periods of time. With autonomous cars, this limitation is gone, so congestion can potentially get much worse unless a new limitation (e.g. cost) is imposed.

    • Novacek November 4, 2016 at 6:05 am #

      Heck, a bunch of teenagers can just get together and have their cars circle the main drag over and over, just to screw with people.

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