Sorry for the flashy headline, but I genuinely feel this might be the best idea I ever had.

After the invention of the horseless carriage, it supposedly took people years to realize that without reins to hold, the driver could now sit inside the cabin. Change of the core technology allowed a rethink of the entire product (the vehicle) but that rethink was hard.

With autonomous cars, we already have a rethink. Autonomous vehicles can be called to a person who needs it, so they should not be owned (and sit idle while the owner doesn't need to move) but should be taxis. Lots of people, including Elon Musk, agree that's the way to go. And it is indeed an improvement over the current car ownership model. But it doesn't go far enough.

The robotaxi concept retains an outdated assumption: that a single product, a single vehicle needs to do both the moving and the accommodation of the user.

Get rid of that assumption and imagine instead a system made from two very different parts that can (automatically) couple and uncouple:

  • A driving unit (tug) with the motor, driving and communication systems. This is usually rented not owned.
  • An accommodation unit (wagon) for the human(s) and their stuff. This is usually owned not rented.

How is this better than robotaxis? Lots of reasons!

  • Your personal wagon can have a bed in it, or your valuables, or spare underwear. You can use it as a movable locker, as you do every time you use a personal car to get groceries from multiple shops. You can sleep in it.
  • Your personal wagon gives you full control over the space you occupy while traveling. A robotaxi requires you to take out your stuff every time you leave and check whether the previous user did every time you enter. And what if the previous occupant used a perfume you're allergic to?
  • The tug doesn't need seats, windows or air conditioning. It doesn't need to haul all that mass every time it is called to a new user. A lot of complexity is removed from production, so these are much cheaper to build than robotaxis.
  • Renting out these tugs is much less hassle than renting out robotaxis because they need much less maintenance. They can be pretty thoroughly protected from interference by users. Charging infrastructure for tugs needs much less space than charging infrastructure for robotaxis.
  • Your personal wagon can be in a huge variety of designs and sizes! Human-piloted cars, and robotaxis, are very hard to build and only make economic sense in huge numbers, forcing standard designs that are suboptimal at specialized tasks. Unpowered wagons are much easier to build, so small production runs make sense. A small-ish company could build specialized wagon types like the self-driving office, the mobile hairdresser's salon or the Sparkly Unicorn Car that takes your kid to school.

Now that I thought of it, I can't unsee it. It seems blindingly obvious this kind of system is much better than robotaxis.

And the technical side wouldn't be that hard to do. You need a standard interface between the two, the wagon needs to give the tug reliable info about its physical properties and maybe it's worth thinking about whether one of the two can make do without a battery. No doubt I'm missing some details, but trains have separated locomotives from wagons for a long time, it can't be that hard.

There's a bit of a chicken and egg problem where you need to be sure the other part of the system will exist before you start producing your own side. But that seems solvable with sufficient clout. If Tesla can indeed demonstrate functioning robotaxis, then Elon Musk saying they're going to build tugs (with an open source coupling interface) should be enough for lots of players to start designing wagons.

So I think it's very doable. And the aforementioned advantages over robotaxis would help get rid of gasoline cars even faster than robotaxis would. And that would help with global warming. So we should all want this.

Am I wrong?

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35 comments, sorted by Click to highlight new comments since: Today at 8:06 PM

It's not either/or.

I no longer own a car, just use a ride share like car2go when I need to get somewhere. Also, I hate owning things. Renting what I need for when I need it and letting someone else deal with the nitty-gritty of maintenance frees my time and my mind. And I am not alone. Most corporate compute is rented. Most commercial space is rented. Most offices are rented. That most houses (in the US) are owned is an artifact of the way thing came to be. If land had no intrinsic value, and renting was a universally more economical option, then real estate ownership would drop dramatically over time.

that a single product, a single vehicle needs to do both the moving and the accommodation of the user

That's a good point. Short trips only need moving, and longer travel needs to include accommodation, though not necessarily of a house-type kind. So, there is some room for what you propose, but probably not for the daily commute, where splitting the tug from the cabin is not necessarily economical. Still, I can see that standardized tugs might be economically viable in some niche cases.

Home ownership is common in part because it has large tax advantages.

You combine some of the advantages of both approaches, but also some disadvantages:

  • you need a parking spot
  • you need to wait for the engine
  • you need to be where your wagon is (or else have it delivered)
  • you can be identified both through your wagon and your regular interaction with a centralized service

You don't need a parking spot - the system can still be used as a robotaxi, it just has additional uses.

You don't need to be where your wagon is, you can send it places. Because of that, you could even rent out your wagon (say you offer a rental sound system or a mobile massage parlor).

...but you could put a bed in your wagon? And you could rent out your bed to massage parlors? I think this system is going to have some hygiene issues with most people...

In a way that Airbnb does not?

Wait how can you use as robotaxi without a wagon? They provide standard wagons?

Upvoted for thinking beyond the obvious, but I don't think this will be popular or common. Accommodation and travel are different enough in character that trying to use the same container for both is going to be an ugly compromise. I travel because I _want_ to move to a different, shared, accommodation than my permanent too-large-to-move home.

Making housing pleasant and efficient, and making travel pleasant and efficient can both be done much more completely by not trying to combine them.

Similar sentiment re: "I don't think this particular prediction will bear out, but I think it's a good use of LessWrong to make concrete predictions and explorations of possible futures".

I think I made a mistake using the word "accommodation". (English isn't my first language.) What I meant is basically "where the people and cargo are stored safely and comfortably". That can be something big to live in, but it could also be a single seat cabin for a commute.

The point is you can have several different types for different purposes, because you don't need to buy an expensive motor and computer with each of them.

You may be right, but I read this more as an argument that we'll keep personal cars, not that we're rent out half of them. If we're sticking with personal wagons, isn't it easier to just own your own engine too? Electric engines are cheap and battery prices are going down.

If you're a first world citizen and able to spend $35k+ on a car, sure. Most of the cars that need replacing are way cheaper, and their replacement needs to be way cheaper too.

According to Kelly Blue Book, the average new light vehicle in the US was $37,185 in May 2019. Replacement pretty much has to happen as a substitution for new car sales, then flowing into the pre-owned markets.

Isn't that just the price of an electric car right now? Won't they be vastly cheaper in the future?

Add to that that the "outdated assumption" says "a single vehicle needs to do both the moving and the accommodation of the user". Perhaps a personal car can be said to "accommodate" people, but if you only want the engine, there's already e-scooters. The whole point of robotaxi is to reduce the number of vehicles needed by making their utilization more efficient (by sharing them). Why should we have those inefficient personal wagons lying around? Why not have houses for "accommodation" and robotaxis for "moving" the people?

It's possible that autonomy changes everything, but things somewhat like this have existed or been talked about:

  • "Modular cars" have been attempted
  • There have been various attempts at swapping the *battery* of an electric vehicle, including by Tesla. (As I understand it, obstacles include: the design advantages of making the battery a structural part of the car chassis; sophisticated battery management that involves "plumbing" the battery into the car's HVAC system). Swapping the battery seems a major move in this direction because the battery is a large amount of the *value* of an electric vehicle. (Conversely: while the vehicle is parked, connect the battery to the electrical grid, and the battery can earn money by arbitraging Watt-hours over time)
  • Obviously, such things as RVs and Winnebagos and caravans exist
  • Cargo containers (and truck/tractors/semitrailers) are something a bit like this, but for cargo

In my view, one big disadvantage of a privately-owned car is that that car's shape has to work for journeys in town, long road trips, vacations, etc, where actually you might prefer something small or shared in town (like a microcar, bicycle, or transit bus) and something roomier for a long journey (or bigger still if you're travelling with friends & family).

Good points.

Agree about the battery swaps, but swapping a tug would be easier.

Cargo containers are definitely like this, but they're big because it is more economical to spread the cost of the driver over a large amount of cargo. Cargo wagons/modules could be in a wide range of sizes, including small/fast ones that are more like courier service than like bulk transport.

  • I'm guessing robotaxis will come first, just because it's easier and requires less coordination between multiple parties, and then the demand for movable lockers will probably be satisfied by, well, movable containers that can go inside the robotaxis and use "AI" to follow people around when outside of the taxis, or maybe initially just containers that people can push around.
  • If "take out your stuff every time you leave and check whether the previous user did every time you enter" turns out to be a big issue (don't people already do this all the time in regular taxis?) the robotaxis could have a narrow AI to scan and detect items that have been left behind, and remind you before you leave.
  • "interference by users" can be handled the same way.
  • Allergy to perfumes seems too rare to matter much, and could be handled by building a HEPA filter into the robotaxis.
  • "A lot of complexity is removed from production, so these are much cheaper to build than robotaxis." But this is actually a "con" for the tugs/wagons model because this saving is more than made up for by the additional wagons that would have to be built.
  • All in all it doesn't seem like your model offers enough additional value on top of the default scenario to overcome the additional coordination and other costs.

Maybe a bit off topic, but to me a future filled with robo-taxis, automated cashiers, drone delivery and other such things would feel kind of scary and alien. I've always lived in cities where you need constant human interaction to get by, and for myself I'd like things to stay that way or even more so.

Customer service human interactions don't feel especially valuable to me, compared to intentional human interactions or even seeing other people walking down the street.


There are plenty (maybe even a majority) of people who would pay a premium for avoiding social interaction with strangers. In fact, early adoption of these automated technologies might be driven by exactly this reason. I think this satire puts it pretty concisely.

My other comment was mostly critical but I just want to add that I really enjoy this kind of post. Any conversation about economics of future technology is fun imo.

Great thinking! However, the trouble is that this doesn't exclude non-autonomous motive sources. For example, why can't you just rent a tug driven by a person for your personal wagon? Additionally, there is a dichotomy of configurability vs availability of motion. You would seemingly have to wait on a tug to go anywhere. Cool thoughts though!

"There's a bit of a chicken and egg problem where you need to be sure the other part of the system will exist before you start producing your own side. But that seems solvable with sufficient clout."

I don't think clout is strictly needed (though it would definitely help)? You start with selling rich people 1 tug plus a bunch of different cabins for different purposes. Overnight trip? Mobile office? Date night? Pick up kids from school? Moderately well-off people follow suit but would like ownership to be less costly. Someone starts an uber-equivalent service. Some tug owners buy an extra and more generic cabin they don't use and use that as a taxi. The system gets entrenched enough that people can have their own cabins and trust a tug-on-demand will be available.

The biggest problems with cars are traffic congestion and parking space. I assume your wagons can be stacked on top of each other? If so, the human world would essentially become a giant warehouse where trucks move human-containers from one stack to another? Doesn't sound so much better than cities with robotaxis.

I'll add a link:

And a quote from there: the future of urban mobility is transit, cycling, and walking, not autonomobiles driven by humans or artificial intelligence. Self-driving cars will never be a mass mobility option, and people shouldn’t be given false assurances to the contrary.

How does either robotaxi or "personal wagon" solve the mobility problem?

Well, here are some ways robotaxis *could* contribute to solving urban mobility:

  • One limiting factor of cars? Congestion. Robot cars, communicating with each other, don't need the safe headways for slow human reaction times, and can - potentially - co-ordinate themselves around gridlock.
  • Trying to travel around on a bicycle? Dumb meatbag drivers may run into you; will robots be better at that? We certainly *hope* so. Same for walking. Also...
  • Parking space! Robotaxis don't have to park right next to the destination - so robotaxis are at least somewhat compatible with high density development, more so than private cars
  • If single-occupant cars aren't providing adequate density, there's nothing to stop the use of adequate-sized buses - something between the size of a minibus and a transit bus - at least out of downtown to "railheads" (the "last mile" concept alluded to).

How feasible is any of this? Hard to tell, too many hypotheticals. The "radical urbanist" article is only interested in scenarios in which robotaxis are completely ineffective (don't work, too expensive) or completely disastrous (cause ultimate gridlock, which no government is capable of doing anything about).

Modern cars have a swish, aerodynamic shape. Would a system composed of two coupled pieces get as good aerodynamics? I agree that there are some advantages to the proposed system, but there are also potential disadvantages.

You need to demonstrate that the cost of division {developing the coupling system, the extra materials for building with the coupling system, and having the two parts be unable to share physical mechanisms} will be less than the benefits of having smaller/cheaper tugs for the few people who really have a use for tugs.

And I think most people don't really have enough of a use for tugs to overcome economics of scale for the near term. The majority of trips will take place with non-custom cabins:

  • The ordinary rider does not need custom cabins. Consider the amount of energy people put into meaningfully customising their homes/apartments in practice (not that much), then scale it down by 20x to account for the fact that people spend a lot less time in transit than they do at home. That's how much people will care most of the time. I should examine some of the usecases though
    • unmanned delivery services only want tugs
    • people who use a wheelchair want a custom cabin they can just roll into
    • People who want to do morning routine stuff during commute want a cabin that supports that stuff? But wouldn't the road movement interfere too much? I mean, have you ever stood in a bus? Imagine having to stay upright through all the shifting and jolting while showering, putting on pants, or eating a meal. If this were a thing, enough people would want it that they could just build a custom car entirely though.
    • Big visiting service station things?
      • Probably bad example: "mobile libraries". A lot of these thingies seem less practical than just having a fixed building provide the service and moving people or goods between them.
      • Hm visiting remote-operated surgery theatres? That could be pretty badass
  • Storing your very own personal cabin, once arrived at your destination, will be an inconvenience. It would mean either sending it to a parking locker (which, if it's in the urban center, you will have to pay a non-negligible amount to reside in), or all the way home again, to then have to wait for it to come out again when they're ready to commute back. I think most people would stop bothering.

Hmm I was gonna say the tugs wouldn't be that much cheaper than common single-occupant cars because they'd need to have enough mass to gain traction on the road, but it occurs to me, if you could have the tug go under the cabin to some extent, then jack it up a bit, it could use the weight of the cabin for traction, so assuming sufficiently dense batteries and motors (can we assume?) it could be pretty small. The heavier the cabin, the more traction it needs, but also the more traction it gets. That's pretty neat.

For completeness, I should link a previous post about the economics of autonomous cars I did (which has comments, and links in turn to another post I did)

Here are more use cases.

  • A specialized cabin for your kid to drive to/from school alone, or for your toddler to drive to/from kindergarten alone. Robotaxis will definitely be used for this because it is super valuable to parents. But a small specialized cabin would be more economical than a standard (typical car size) cabin fitted with child seats.
  • Visiting dialysis station.
  • Specialized delivery cabins for particular types of cargo: refrigerated, extra suspension, stuff for transporting animals. We do this with trucks, but trucks are big because they're optimized to need less human drivers per mass of cargo, and once that restriction is gone the disadvantages of big trucks should incentivize a move to smaller cargo vehicles.

I think these three are major enough that even if we stay with single vehicles, these use cases would merit development of specialized robotaxis to cover them, sooner or later. But a tug and cabin system gets there sooner.

Specialized cabins seem like they would hurt this idea – where would people store all of their cabins?

In a car park? But they will be way more densely packed than cars in car parks, because no humans need access. The cabins get placed there and retrieved from there by autonomous engines.

Good answer!

I was thinking about people living in detached homes in residential neighborhoods, i.e. places where I would expect local politics to prevent car parks ('parking lots' in my colloquialisms) from being built at all.

Sounds good! I think many people would forego the luxury (parking spaces are expensive in cities & for a lot of people the transportation itself is enough), but I can imagine some part of the market being like this

Not wrong I think, as most others do as well it appears. But I think it better seen (as others note) as a good insight that has a place in the large mix rather than as some complete alternative to the current thoughts.

That seems to be a fairly normal trajectory for innovations -- they need to work at the edges. So the autonomous vehicles get started in places like mining where it's a more controlled and limited setting or factory floors. Slowly they can move to broader application, truck fleets (while I've not heard of them I would think something like patrol boats for customs would be something of a no brainer) and then into things like moving people via taxis.

I think the idea of separating the engine for the compartment just works into that a bit more slowly as the applications (an standards for coupling) get worked out. I would think the coupling aspect might be the area to start working on as that doesn't seem like it's on anyone's radar (though perhaps research in mining and rail yard areas might show something) but might dovetail well with existing plans - such as taxis. For instance, with urban travel (and perhaps even more so in suburban, not sure) it is likely that trips originating at one location, or even along a common path, could be more efficiently services even when the end destinations are vastly different with one taxi engine for part of the trip then one of more of the passenger containers disconnected at some point to where another taxi picks it up for the next led. Probably good logistic support could be found with rail management tools for starting points.