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

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.  read more »