The rise of the small and narrow vehicle


Many of the more interesting consequences of a robotic taxi "mobility on demand" service is the ability to open up all sorts of new areas of car design. When you are just summoning a vehicle for one trip, you can be sent a vehicle that is well matched to that trip. Today we almost all drive in 5 passenger sedans or larger, whether we are alone, with a single passenger or in a group. Many always travel in an SUV or Minivan on trips that have no need of that.

The ability to use small, light vehicles means the ability to make transportation much more efficient. While electric cars are a good start (at least in places without coal-based electricity) the reality is today's electric cars are still sedans and in fact are heavy due to their batteries. As such they use 250 to 350 watt-hours/mile. That's good, but not great. At the national grid average, 300 wh/mile is around 3000 BTUs/mile or the equivalent of 37mpg. Good, and cleaner if from natural gas, but we can do a lot more.

Half-width vehicles have another benefit -- they don't take up much room on the road, or in parking/waiting. Two half-width vehicles that find one another on the road can pair up to take only one lane space. A road that's heavy with half-width vehicles (as many are in the developing world) can handle a lot more traffic. Rich folks don't tend to buy these vehicles, but they would accept one as a taxi if they are alone. Indeed, a half-width face-to-face vehicle should be very nice for 2 people.

The problem with half-width vehicles (about 1.5m or 4.5 feet if you're going to fit two in a 12' lane using robotic precision) is that a narrow stance just isn't that stable, not at decent speeds. You like a wide stance to corner. One answer to that is the ability to bank, which two-wheeled vehicles do well, but which requires special independent suspension to do with 3 or 4 wheels. 2 wheels is great for some purposes, but 3 and 4 have a better grip on the road, particularly if a wet or slippery patch is encountered.

There are quite a number of 3 and 4 wheelers with independently adjustable wheels made. Consider the recent concept I-road by Toyota which exemplifies this well. There are however a number of vehicles that are not concepts, and this (rather long) Gizmag video provides a summary of a variety of real and concept vehicles in this space, as well as enclosed motorcycles and scooters, including the Nissan Landglider, the VW 1L, the Twizzy, the Tango, the Lumeno Smera and many others. Skip to about 13 minutes to see many of the 3-wheelers. Another vehicle I like is the Quadro -- Watch this video of the 4 wheel version. These vehicles are aimed more at the motorcycle market and are open, while I suspect the single person robocar will be an enclosed vehicle.

I also wrote earlier about efforts on two wheels, like the concept vehicle the Twill. Other recent efforts have included the gyro-stabilized Lit Motors C-1 which can be fully enclosed on two wheels because you don't have to stick your legs out.

I suspect the 4 wheeled bankable vehicles are the ideal solution, and the technology is surprisingly far along. Many companies prefer to make 3 wheeled vehicles because those currently get classed as motorcycles and require far less work to meet regulations. These exemptions are reportedly ending soon, and so the effort can shift to 4 wheels which should have the most stability.

The ability to bank is important not just to stay stable with a narrow stance. Banking also means you can tilt the passenger to make turns more comfortable in that the force vector will be mostly up and down, rather than side to side. In a turn it feels more like getting heavy and light rather than being shifted. Some people, however, will have trouble with motion sickness if they are not themselves looking out the window and feeling part of the banking move. Being able to tilt forward and back can have value so that starts and stops also produce more up and down force vectors rather than forward and back. While this is not yet demonstrated, it may be possible to make vehicles which provide minimal discomfort to many passengers when doing things like turns, stops and the roundabout. Roundabouts seem like a great idea for robocars in many ways, since you don't need to have stop signs or lights, and robocars should be able to insert themselves into gaps in traffic with precision and confidence. Frequent roundabouts, however, would be disconcerting with all the turning and speed changes, to the point that many would prefer just a straight road with timed traffic lights, so that a clever car that knows the timing never hits a red.

Another entry in the narrow vehicle field that got a lot of attention is the autonomous driving Hitachi Ropits. The Ropits -- here is a video -- is a narrow vehicle with small wheels, and is able to be autonomous because it is super-slow -- it only goes 3.7mph -- you can keep up to it with a brisk walk -- and is meant to go on sidewalks and pedestrian lanes, more of a mobility for the aged than a robocar. However, it is a new entry in the autonomous vehicle pantheon from a new player.

The big question that remains about these vehicles is crash safety. As motorcycles they are not receiving the same sort of testing. In a world that is mostly robocars, one could argue that you don't need the same levels of crash safety, but we aren't there yet. All is not lost, however. Recently I sat in a prototype of the Edison2 Very Light Car. The VLC is a 4-seater with a narrow body but a wide stance, for handling. This vehicle has been crash tested with good results, and it could be made with independent suspension and banking and a narrower stance if the market wanted that.

Small vehicles, just 4.5 feet wide and 10-12 feet long can make a huge difference. First of all, they are inherently (except the Tango) going to be light, and light is the most important thing in making them efficient. But they will also take up less space on the road, able to go 2 to a lane (or even lane split in some places.) They will also take up much less space parking. The combination of their small size (about 1/3 of a typical car) and their ability to pack close together "valet style" as robocars means you will be able to fit 4 or 5 of them in the same amount of parking lot area that today fits a single car in a non-valet lot. As noted, while many robocars will not be parking at all because they will be taxis that head off to get their next fare, those that do wish to park will be able to do it at vastly greater densities than we have today, and the consequences of that are big.

There are a few other options for increased stability with normally narrow stance. These might include:

  • Low center of gravity -- this is what the Tango does, filling the very bottom with lead-acid batteries. Passengers might sit lower -- some vehicle designs involve lowering after the passenger gets in.
  • Variable stance: a possible ability to widen the stance with an extendable axle so the vehicle takes a whole lane when in places that need that cornering ability and stability.
  • Extra wheel: The ability to temporarily deploy an extra wheel (probably not a drive wheel) to one side or both to temporarily increase stability. This wheel might take all the weight on that side, or balance with the others. Vehicles side-by-side could even coordinate to still fit in a lane but that sounds risky.
  • Just go slow: Narrow stance vehicles might just be used in lower speed urban routes, and take corners fairly slow.
  • Gyroscopes, under robotic control.

It's important to consider that the risk of instability in a narrow vehicle is mostly one for human drivers, who are used to wide stances and may make errors on the physics. A robocar, with full knowledge of the vehicle's characteristics and the shape of the road simply won't try any turn that would tip it, and it won't pick routes that have turns that would require the vehicle go so slowly as to impede traffic. Knowledge of road traction can complete this sort of analysis.


These types of vehicles will be very important to drive down the cost of the shared driverless fleets. I think it is about 70% of all trips are 1 person, and 90% with 2 or less. Therefore about 70% of vehicles could be made for 1 person. The tandem seating or face to face seating, slim profile seems the obvious way to go. Once these are developed even the masses in poor regions will be able to afford this technology.

Yes, I think the face to face vehicle will be a likely choice. That vehicle is not that inefficient for a solo rider, and offers the option of forward or back facing. Most people prefer forward but back facing is slightly safer. If two people sharing just want to work they may prefer tandem. Reconfiguration is also possible but takes a bit more room. F2F with a table between, or a dual-sided monitor/wall that flips down from the roof could also be good.

I should have pointed out that in many parts of the world, half-width vehicles -- known as scooters -- are the norm already. These vehicles can actually be more efficient than scooters, particularly at higher speed, due to the fairing which reduces drag.

And in time, these small vehicles will also be cheaper to make than sedans.

As you point out, the issue is crash safety. There are any number of really awesome things you could do with small, light vehicles, but they're all deathtraps in a collision.

What we have learned over the years is that in an automobile crash, what saves you from serious injury is distance between you and the impact. There are various tricks you can play with airbags and deformable structures to increase the effective distance, but ultimately you need X number of inches for Y degree of reduction in crash energy, and these minicars are not going to have that.

The other option is to reduce the crash energy, which implies some kind of national speed limit enforced by mandatory governor installation. And that will be...difficult, we'll say, to sell.

Although, maybe not as difficult as we might think. "Automobile hobbyists" can set up an autocross association that rents governor-free, track-only cars to its members (and the truly rich/dedicated can buy their own.)

Well, that's what the Edison2 team is claiming is not true, they think they can make a small and light car that's crash safe, and that they have done it. Admittedly their vehicle has the wheels out to the side for a wider stance, and this does assist in the crash safety. You can put the wheels out more to the front (longer wheelbase) to get forward and rear crash safety, and that is indeed the most important kind, but I agree that side crash safety in a narrow stance vehicle is more challenging.

That doesn't mean we can't work out methods for such safety. If we can't, it does change the equation a bit, at least until the accident rates drop enough that we can afford less side crash safety. Before then, we might just not use the narrow vehicles on highways and limit them to the city.

But I think there's a lot of unexplored territory here, especially when you consider that the robocar will not be surprised by a crash. It's sensors will see an impact coming well ahead of time (for a computer) and if it can't be avoided, will be able to do things pre-crash that have never been done before, like extending out a bumper to the side or front that then collapses back in on impact.

It will also be interesting to see the geometry of lots of side impacts and figure out if a smarter car could avoid a lot of them with clever braking or electric-motor 0.9g acceleration, given a second's advance warning.

For most errands, an autonomous "errand car" will be much smaller and use less energy. Why use a 4000-lb SUV to pick up a Quarter-pounder? Worse is seeing lines of cars at Starbucks, picking up lattes. That's a huge waste of human time, vehicle overkill, and wasted fuel, to get some hot flavored milk. Driverless vehicles, about six years away, will yield to autonomous driverless vehicles that will be really small and run all our errands.

I have much more to say about the evolution of vehicles and transportation of goods, but I'm filing a provisional patent application with the USPTO soon, on a much more advanced concept.

85% of car trips involve a single-passenger/driver. One-person enclosed vehicles should dominate the roadways.

What I like to call the deliverbot was actually the goal of the first Darpa grand challenge. I have several articles about them, and they would tend to mostly be quite small. No need to provide safety for their cargo -- still need safety for those outside. No real hurry for most of them, either. Small robots for single packages. Larger ones with shelves that open for the recipient (who is never visited unless they are there and ready to receive) for multi-item deliveries. Heated ones, cold ones made for food of all sorts. And a few big ones for the big items, but those are rare.

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