No, the car sharing aspect of robocars isn't as exciting as people hope

Submitted by brad on Wed, 2013-08-14 14:03

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Frequently, in reporting on robocars, it is often cited that one of their key benefits will be the way they enable car sharing, greatly reducing the number of cars that need to exist to serve the population. It is sometimes predicted that we'll need to make fewer cars, which is good for the environment.

It is indeed true -- robotaxi service, with cars that deliver themselves and drop you off, does greatly enable car sharing. But from the standpoint of modern car sharing, it may enable it too well, and we may end up having to manufacture more cars, not fewer.

Today's car sharing companies report statistics that they replace around 13 privately owned cars for every car in the carsharing fleet. Some suggest it's even as high as 20.

This number is impossible for average drivers, however. The average car is driven 12,000 miles/year. To replace 13 average cars would require a vehicle that was actively driving, not just signed out, 11 hours/day and each vehicle would wear out in 1-2 years.

Three things are happening.

Carsharing is replacing the more marginal, less used vehicles. A household replaces a 2nd or 3rd car. Carsharing is almost always used by people who do not commute by car.
Carsharing is often considerably less convenient than a private car. It discourages driving, pushing its users into other modes of transport, or selecting for customers who can do that.
Related to that, carsharing shows the true cost of car ownership and makes it incremental. That cost is around $20/hour, and people rethink trips when they see the full cost laid out per mile or per hour. With private cars, they ignore most of the cost and focus only on the gasoline, if that.

The "problem" with robocars is that they're not going to be worse than having a private car. In many ways they will be better. So they will do very little of the discouragement of car use caused by present day carshare models. The "dark secret" of carsharing is that it succeeds so well at replacing cars because of its flaws, not just its virtues.

Robotic taxis can be priced incrementally, with per-mile or per-hour costs, and these costs will initially be similar to the mostly unperceived per-mile or per-hour costs of private car ownership, though they will get cheaper in the future. This revelation of the price will discourage some driving, though robotaxi companies, hoping to encourage more business, will likely create pricing models which match the way people pay for cars (such as monthly lease fees with only gasoline costs during use) to get people to use more of the product.

There is an even stronger factor when it comes to robotaxis. A hard-working robotaxi will indeed serve many people, and as such it will put on a lot of miles every year. It will thus wear out much faster, and be taken out of service within 4-5 years. This is the case with today's human driven taxicabs, which travel about 60,000 miles/year in places like New York.

The lifetime of a robotaxi will be measured almost exclusively in miles or engine-hours, not years. The more miles people travel, the more vehicles will need to be built. It doesn't matter how much people are sharing them.

The core formula is simple.

Cars made = Vehicle Miles Travelled (VMT) / Car lifetime in miles

The amount of sharing of vehicles is not a factor in this equation, other than when it affects VMT.

Today the average car lasts 200,000 miles in California. To be clear, if you have 8,000 customers and they will travel two billion miles in 20 years (that's the average) then they are going to need 8,000 cars over those years. It almost doesn't matter if you serve them with their own private car, and it lasts all 20 years, or if you get 2,000 cars and they serve 4 people each on average and wear out after 5 years.

There is some improvement over today's cars, but less than you expect. Today's cars also mostly wear out by miles. Some things, like those exposed to the sun, wear out by the year, but not too many. You can store and garage a car that is not being driven and it will stay in great shape for decades with very minor maintenance.

One thing that does wear out with time in today's cars is the technology. Thanks to computers and other tech advances, newer cars have more features than old cars, and so are more valued even then low-mileage old cars. This is a boon for robocars, which will be very technology dependent. We'll be glad they are wearing out in 5 years.

The smaller differences

I said it almost doesn't matter. There are some gains to be had by sharing. They are not trivial but they are not the huge win that people hope.

There is less capital investment to buy 2,000 cars every 5 years than to buy 8,000 and hold them for 20 years. Right now, capital is cheap, so the total interest cost is just a few percent of the total costs.
As noted, your cars have newer technology as the years past -- a vital element for many.
You only need to store 2,000 cars, so you need a lot less waiting space (what used to be parking spaces) and very few parking lots and garages. That benefit was already coming from robocars that can park themselves more densely in available space some distance away from the target location, but this makes it even stronger.
Thanks to recycling, the total amount of steel and certain other materials tied up in vehicles goes down.

These advantages pair off with some of the disadvantages of car sharing:

Potentially longer wait times, and rare situations with particularly long waits at peak times.
Hard to keep your "stuff" in the car.
Harder to personalize your style using your car, as people like to do.
Less ability to make your car be just what you want it to be without increasing wait time.
Logistics of billing, management, damage/soiling.
Wasted energy and pollution from empty car moves, which increase the VMT.

There is one factor that may alter these numbers. Today cars are built to last 200,000 miles and 19 years. Future robocars will be engineered with different lifecycle goals. Many of today's cars often last much longer than 200,000 miles with more attentive maintenance. Cars designed to reliably last 300,000 or 400,000 miles (but just 5-10 years) might make a lot of sense. Make cars last 400,000 miles and you only need half as many cars, and that's a huge saving, worth paying a fair bit extra for in the cost of the car and its maintenance.

The lifetime of today's cars is a complex beast. One sector of the market sells their car when it is 4 years old. They always want a late model car and will pay for it. Those unwilling or unable to spend that on a car buy used cars and make use of the latter years of a car's life. Some people, regardless of income, are happy to buy one car and wear it out directly.

Often that "wearing out" point comes when the car needs a repair, and this repair clearly costs more than its worth doing on such an old car. Cars engineered for a different lifecycle could be designed to make this happen smoothly and extract more life per dollar from the cars.

A car's interior also wears out as people sit in it. Dirt and damage accumulate, the leather or plastic wears out or cracks. A car with 250,000 miles on it does not have a nice, shiny new interior the way people like. To last this long, cars must be designed with planned maintenance to the interior as well as the moving parts. A car's finish in part ages with years but also with driving. With luck the robocars will face fewer scratches, but they'll still get dinged by stones on the road.

Sharing a ride

Another factor which could reduce the total VMT is to get people to share rides, not just vehicles. There are many companies out there trying to make that happen with regular cars, but success is modest. There is much more potential with robocars for serendipitous ride sharing that minimizes inconvenience. Here, the system would notice two people who literally are travelling the same stretch of road at almost exactly the same time, and arrange a share. This is highly efficient. Unlike other approaches to ride-share, this can work because individual cars can take some of the sharers on the disjoint parts of their route. So you get in a small taxi that takes you to a parking spot somewhere, where a multi-person car has just pulled up. You get in, share the ride until your paths diverge, and then the car pauses beside another single person car that takes you (or one of the others) along their quick path. Everybody travels almost exactly on their optimal route, and inconvenience is minimized.

Such a system could increase average occupancy. That in turn would drop total vehicle miles travelled, and reduce the total amount of cars needed to be made.

There are many other robocar factors that might change VMT, which changes now many cars must be made:

Robocars may encourage longer commutes and sprawl. They might also encourage tighter neighbourhoods too.
Deliverbots will eliminate many shopping trips. They will be much simpler and cheaper than passenger cars.
People will switch many trips from transit to cars
Personal taxi service (parent taking the kids to soccer practice) might be reduced, cutting miles for such trips in half. On the other hand, children may travel more where today they must beg a parent.
Some really long trips (like sleeper cars) might arise.

Summary

At least with today's car designs, robocars will not reduce the number of cars made as long as people travel the same number of miles. They might even travel more miles, and require empty vehicle moves, meaning that more cars are made per year, though only modestly more. Car sharing of vehicles that are designed to survive many more miles than today's cars would reduce the number of vehicles manufactured each year.

A side note: You will note I have often referred to a car's life in engine-hours. We almost universally use miles to calculate wear and tear on cars, but I think hours would be much better, and cars actually do record this in their internal computers. Highway driving at 70mph racks on the miles but is fairly low-stress, and even lower in accidents. Lower speed city driving with starts and stops puts more wear per mile on a car. Hours are not perfect, but they are better.

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