Yesterday, Volvo got some good buzz for a concept car which included a bed for sleeping and asking the question "why fly when you can be driven?". I've written about sleeper cars before, as well as the full robo-RV, but let's put all the issues together.

Obviously, if you can sleep while you travel, it's magic, because you can make the travel take no time at all. Those who sleep easily on planes (not me) actually view red-eyes as their preferred flights. There is the potential for the sleeper car to be the cheapest and most efficient vehicle on the highway, and create a whole new style of travel.

• Compared to a plane (and even a train) space can be at less of a premium.
• If you have a car which is only a sleeping car, you can actually make it super low to the ground, which can give it much less drag, for more efficiency. In fact, the solo sleeper car should be the most efficient passenger vehicle on the highway.
• If the passenger wants a full night's sleep, the car can prefer to go at a slower speed (as long as that doesn't impede traffic) for even more efficiency.
• Like all robocars, with no need to have the driver "feel the road" one can use a dynamic, super-soft suspension to make the ride more comfortable, though perhaps not as smooth as a plane with no turbulence or a high quality rail line.
• The problem of seatbelts and airbags for a sleeping passenger may be more challenging than for a sitting one. While accidents are more rare, they will happen.
• For overnight trips, a place to change clothes and do morning ablutions is also needed.

There are a few situations where people might like to sleep:

1. Overnight trip to city 250 to 500 miles distant
2. Family trip to vacation home. Load family Friday night, arrive Saturday morning. Load family again Sunday night -- more total wake-time at destination than day-driving.
3. Commuter with long commute sleeps less at home, completes sleep on the way in. Possibly also naps on return.
4. "Nap" car -- for those who get drowsy on any trip.

The latter two choices are easier in a car that converts -- ie. a seat reclines to a bed. They can also be done in a dedicated sleeper car if, once you waken, the car pulls over to meet up with a normal robotaxi with upright sitting. A family sleeper needs a toilet, which makes it a fair bit bigger. Large family and group sleepers could have two levels of bunks.

The morning commuter car, good for 1-2 hours of sleep, is the easiest. It doesn't need a toilet or place to change. By making 2 hour commutes tolerable, it would increase sprawl and exurb development, and waste energy. Group commuter cars, which bunk 4-8 or even more people and use single person pods to bring solo passengers to and from them, could provide an efficient option. Pity the person who decides after boarding that they can't sleep.

Sleeping on the morning commute is an obvious thing. It's a little more difficult on the return for most. Employers don't want you in "needing to sleep" mode in the last few hours of work. However, the natural human sleep cycle actually is an early rise and a post-lunch siesta nap. It might be possible to adjust this to the commute regimen.

Of course, it's always possible to make vehicles like the Volvo, which convert and have both nice seating and a bed, and enough space and height for a toilet or working -- like fancy first class seats on overseas planes. But this comes at a serious cost, both in the price of the vehicle and the energy use.

Why the focus on efficiency?

In spite of what Volvo says, trips of 400 miles in group vehicles, like planes or trains (or buses as I'll describe) are more efficient than a solo trip in a larger and heavier vehicle like their concept. However, it's right on the line, and so if the vehicle can be low-slung or slow, it's going to beat the plane. And it's always better to use less energy.

This is even easier if the vehicle is electric. While having a 500 mile battery (which weighs a lot) may not be the right choice, if the drive takes less than 8 hours, a sleeper car can pull off (using very gentle and planned stops) at charging stations designed for a recharge during the night. An electric sleeper will beat the airplane for energy use.

The low-slung solo/couple sleeper might be the cheapest highway-capable car there is. In the electric design, it would feature just a base, 4 wheels, suspension, a battery pack with mattress on top, roll-bars and crumple structures, airbags and restraints and a simple fiberglass dome roof that hinges on one side to lift up. Perhaps a small window for comfort but possibly not even that. No big screen, big speakers, buttons or knobs or adjustments. Charging for your devices, small speakers and a small screen and an emergency exit and that's about it. Even the ICE version is simple with a small engine (no need for fast acceleration or power unless it's doing the mountain routes.) With no chair and no need for things to occupy you, it's the cheapest vehicle on the road. And if it's just 3' wide (solo) or 5' wide (couple) and slung low, it's also the lowest drag vehicle on the road. Adding an aisle and some height to bet to the toilet makes it bigger and more expensive. Making it an RV probably makes it 4x to 5x more expensive. Which means the solo ride costs that much more too.

Follow-up on efficiency of solo transport

I write a follow up article on the surprising efficiency of solo transport when it comes to sleepers. It provides more comment on this and other issues.

The toilet

For overnight trips, the need for a toilet provides all sorts of challenges. That's not practical in a low-slung bed-only car. While some (men in particular) can use a bottle lying in bed, it's nobody's preference. Those who always go the whole night without need to pee could handle a car with no toilet (or a bottle for rare urgent needs.)

Around 55% of people don't routinely wake up during the night to pee, but the rest do it 1 or more times per night.

Of course, our highways today are full of rest stops because regular road-trippers regularly need the toilet, and so your sleeper car can pull over, though again, having to go outside for the joys of a public toilet is rarely a first choice. And nobody would like waking up with the need to go, and then learning it's 10 minutes to the rest stop. You can't go back to sleep with that pressure so your sleep is more disrupted. Those with a predictable pattern can program the car to stop and wake them when it's almost time, which can solve this problem.

Family and group sleeper cars also will run into trouble, because people have needs at different times, and parents don't want kids going out on their own to public toilets in the middle of the night.

An on-board toilet and small sink can of course be done, and the car can travel after the trip to a depot for draining and cleaning. The main issue is it costs a lot of space and height -- you have to be able to get out of bed, get to it and then sit or kneel as need be. Suddenly the vehicle needs an aisle, and more height -- it's a large cost to get this, but many people will insist on it.

For those willing to pay -- which might be many because I think having an on-board toilet might double the cost of the ride -- the roadside rest-stops could be high-end, where the electric car actually drives into the bathroom and a garage door closes behind you to allow you a private visit.

A toilet bot?

One could also imagine a vehicle whose only function is to be a roving toilet. They would not go fast or far, but when you indicated the need for one, it should probably be able to meet you along the shoulder (in a safe section, possibly added for this.) Your car and it would dock touching one another, so you just step out of bed right into it. Every so often, they would head off for draining and cleaning and return to the popular late night routes. If sleeper cars were standardized enough, they could even "dock" in an enclosed way, so you don't have to get exposed to the cold too much. These would even be popular with daytime drivers and human drivers. They would be only for urine. For #2 use a regular rest stop.

Slow cars

For a family car to a vacation home 4 hours away, you want the car to go as slow as possible. In fact, you would be so slow that this would annoy other people who are in a hurry. Of course, with a vacation home, the early arriving car can park and people can wake up whenever they like, even after a full night of sleep.

Slow cars on the road would be polite -- always pulling over if somebody comes up behind, and possibly sticking to minor roads, though they will prefer not to have lots of stops which disturb their passengers.

One radical idea is that, late at night, cars could pull over to the left, which is to say into the oncoming traffic, to allow a fast car behind them to pass. With a map of the geometry of the road, and the ability to detect oncoming headlights at a long distance, slow cars could know when it was safe to do so. They would even slow a bit while doing this. The fast car would pass quickly. The sleeper car could even flash a signal to the fast car that it is going to do this, allowing the fast car to zoom through as if the slow car wasn't even there. At night, traffic is light enough that this should work. On the highway, sleeper cars would of course keep to the slow lane.

Group sleeper vehicles

One very efficient vehicle would be the group sleeper -- effectively a bus full of bunks. Everybody wants to go overnight, and adding a shared bathroom, and even an aisle is not as much of a burden. (It should be noted, though, that otherwise a vehicle can have no aisle because people can have doors to the outside for their bunks.)

In fact, this already exists -- the group sleeper is efficient enough that the cost of the driver is not as big an issue. A service called Cabin drives between SF and LA with bunks and even a small kitchen. When it gets to its destination, it sits in the parking lot for 2 hours for those who wish to complete 8 hours of sleep. (Update: Cabin went out of business.)

This practice is also common in some places on trains, and on the Baltic in ships. It's particularly popular to travel from Helsinki and Tallinn to Stockholm on these ships. The price is attractive if it saves you a night in a hotel room, and they also offer meals, gambling, duty free and some sightseeing for the tourists.

At the same time, it is important to understand the vast difference between a solo sleeper and a group one in convenience. A solo sleeper can take you from your driveway to your staging destination on your sleep schedule. When you get tired you would do everything you normally do to get ready for bed, put on your PJs and instead of going to the bed, walk to the driveway and climb into bed there. If you are one of the lucky people who falls asleep quickly, next thing you know your vehicle is parked inside your staging destination (a place where you can shower and change.)

With a group sleeper, you must fit your night to their schedule. You must travel (presumably not in a bed) to the departure point, and get there with enough margin to be sure you make it. All of this is probably done awake. You could easily see the group sleeper involving 10 to 100 times as much awake travel as the private one, and only awake travel time counts for this type of customer.

Compared to the airline

It's early for Cabin, but I don't think it's a big threat to the airlines. Volvo points out the nightmare that short-haul flights have become, with 3 hours of travel with only 1 hour of flying. The "teleport" aspect of sleeping can be attractive then, except for two things.

1. While you might want to be there in the morning, the teleport illusion only works if you also want to stay until late in the night as well.
2. The airline nightmare is fixable, if we have the will -- we have done this to ourselves. If the airlines started facing real competition from overnight sleepers, they will adapt, because they have to.

Vehicle design

As noted, the single person sleeper, just 3' wide and 8' long and 4' high, could be the cheapest and most efficient vehicle on the highway. Here are some possible layouts:

• Couple's car, 5' wide bed
• Family car with 5' wide bed, and transverse berths (only 5' long) for children under 4'10" in height
• Family or group car with 2 levels of adult berths for 4, 8 or more passengers.
• Wider solo car with diagonal bed for more safety and two triangular cargo spaces.

However, in need of more research are the best designs for safety. While the best aerodynamics are higher at the front and coming to a point at the back (teardrop shape) it's probably not good to be riding headfirst, at least in forward impacts which are the worst of all.

It's also hard to figure how to restrain people lying feet forward. No matter what direction, one idea might be a webbing which can descend from the ceiling after bedding down, and then tighten hard before an accident.

Transverse bunks are probably much better for restraints in forward and rear accidents. Side impacts are not very likely on the highway. However, for adults, that requires a car almost 7' wide which is bulky on the road and low efficiency. It does make having toilet space easier. Cars could actually come in different sizes and you would get one with bunks big enough for you (or larger.) Robocars can handle being 7' wide as they will remain reliably centered in their lanes -- it's just a question of drag. Airbags also will work better with a passenger perpendicular to the direction of travel.

To get more advanced, a bed (particularly a transverse one) could be on actuators which could quickly tilt the mattress almost vertically. You would then deal with the impact by being slammed hard into the mattress, spreading the shock over your whole body and deep into the mattress. The mattress might be extra thick. Combined with crumple zones the severity of impact could be much less.

Question for readers

An unscientific survey: If taking an overnight sleeper ride, would you insist on a comfortable toilet/urinal, if that ride cost twice as much as a car with only a bunk and an emergency bottle? Indicate if you are male or female.

Answer this question via this poll page. Not in the comments unless you wish to add more thoughts.