Does your robocar come home after it takes you to work?
This week we've looked at two issues regarding robocars in the city:
- How to handle the "pick up rush" when thousands want to leave a place (like work, movies, schools, stadia or airports) at the same time
- How we should manage the street parking and free parking in a city
Now let's consider another common question. Will owners of private robocars send their car home after the commute to park, or serve other members of the family, particularly as an alternative to having 2 cars?
Yes, some people will continue to own cars, even when it's much more expensive
I see a lot of debate over whether people will own private robocars at all. Many people imagine the robotaxi proposition -- Uber style service at a price that matches or beats the overall cost of private car ownership -- is so compelling that they can't fathom why anybody would own a car still.
The proposition is compelling. Eventually use of robotaxis will be superior in almost every way, from a purely rational business. At the same time, some forces will push some people into ownership
- Living or working in an area (such as rural areas) where fast robotaxi service is not available
- Ability to keep a variety of things in the car, not just between stops, but always. (I admit to doing this myself.)
- A guarantee that the car you like will always be available to you on short notice. No long waits, no surge pricing.
- Ability to show off your wealth and status.
- The private car may also offer manual driving and perhaps be sporty when you want it.
- Particular tastes not served by the robotaxi market
- Inertia and stubbornness -- ownership is how we've always done it. And many other irrational reasons.
Yes, private ownership will eventually cost thousands of dollars more per year than robotaxi use -- but even so, some will choose it and can afford to.
It does not matter that you don't think these reasons are compelling. There are others who do. So there will be private cars, even at higher cost.
Households with 2 or more driving age people will choose between having 2 private cars, having 1 private car and having none. Even for the car owner, the middle case may be the most compelling mix of the two worlds.
If both people commute, and there is only one car, they will have to choose who gets to use it in the commute. There are arguments in favour of either person. Whose commute is longer? Who needs a private car more often while at work? What does it cost to park near the workplace and how close can you park? Are the commutes at the same time? And how does this match with the kids' commute to school?
If only one person commutes, there can still be a choice about them using the car or not. Many one car families have the commuter use transit or carpool if they are convenient, to keep the family car at home for the person who does not commute, and for the kids' commute.
Let's consider a family, Taylor and Jordan, where Taylor has a traditional commute to a business district, and Jordan either has a commute at very different times, or does not commute at all, but does other trips and errands during the day. There may also be kids needing transport to and from school.
Does it make sense for Taylor to commute in the private car, then send it back for Jordan and the kids? I'm still looking to get a good handle on the incremental cost of extra vacant miles in a vehicle, but a decent rule of thumb is it's probably about half the total cost, which is the mature robotaxi price. So, for example, 50 cents/mile for robotaxi, and 25 cents/mile for incremental mile in owned car.
If Taylor gets free parking at the workplace, the answer is to not send the car back. If Jordan's use is fewer miles than Taylor's commute, it's cheaper to use a local robotaxi rather than send the car back. If Jordan's use is greater, it flips -- but then it makes sense to just have Taylor commute by robotaxi and have Jordan keep the car, because that's cheaper. In fact, a simple way to see it is that the cost of Taylor just using a robotaxi at 50 cents a mile is equal to the cost of Taylor using the private car at 25 cents/mile but doubling the miles due to the return trip, with the downside to Jordan of need to use robotaxi during those round trips.
It gets even cheaper if Taylor has the option of robotransit which provides a trip similar in duration and comfort to a private ride, but at a much lower cost. In fact, if that's available, it's the clear choice for the commute, unless Taylor has regular need for the car while at work.
The vast majority of commuters actually get free parking at their workplace, and the ability of robocars to densely park "valet" style in 1/3rd the space means more probably will. It's also quite likely that employers, rather than provide parking, will subsidize employee commute rides.
Pay to park at work
The need to pay for parking at work will alter the equation. I estimate a cost for dense-packed robocar parking on a monthly basis of around $4/day in typical CBD regions, less in less-dense zones. Now, just looking at the cost, it can make sense to send the car back if Taylor's driving does not exceed Jordan's by 16 miles. The complete formula for the difference in cost between keeping the car at work minus the cost of sending it home is: J/4 + P - T/4 and thus to make it work sending the car home you need: T - J < 4P
This can get more complex because Taylor doesn't have to send the car all the way home. If it is send just one mile to where parking is $2, effectively the cost of P is now just $2.50, and now the margin must be within 10 miles. But it also moves the needle to where it again makes sense to have Taylor commute in the robotaxi (and pay no parking.)
Different vehicles, and hiring out
Indeed, vehicle type plays a role in this math as well. Buying and operating larger vehicles will cost twice as much as single person commuter vehicles. Few families today buy a single-person commuter car, but this is the most efficient and economical choice for a solo commute and should be a common robotaxi offering.
It may very well be that the commute can be done in a 30 cent/mile robotaxi meant for one person, leaving the more expensive 4-seat private car at home. While the private car's incremental cost is less than the robotaxi, it's not much less, and the robotaxi continues to be the winning choice.
Another entrant in this equation is hiring out the commute car as a robotaxi while at work. This eliminates some or all of the parking cost, and possibly brings in some income on the vehicle. While doing this, Taylor may not be able to use that car for an unexpected ride, but a robotaxi would be available.
It should be noted that sending a car home is probably not a very convenient style of use. It means Taylor can't use it during the day and must use robotaxis. It means the car is not available to Jordan until 9:30 or 10am, and not after 4:30pm. Thus it may not be available for dropping kids at school, though it might do pick-up.
Once again, the decision may be based on factors other than the math, like those listed above. If Taylor has a very short commute, then there is not that much inconvenience to Jordan, and even though that short commute is no more expensive in a robotaxi (due to the round trip) the desire to have one's own car may win out.
The deeper question will be about the social consequences of these decisions. If it's an economic wash, it's not a social one. The empty round trips add some congestion to the roads -- though it is mostly, but not entirely in the reverse commute direction. (Some places have high demand in both directions.) The empty round trip also creates emissions from its energy use, whose externalities are not priced into the energy cost. And while it is priced into those per-mile prices, the extra driving creates extra risk of accidents. If the choice is to not create the risk at a slightly higher cost, or have the accidents and use the money to fix them, it's obvious what choice we want.
The only reason this question even comes up is that when people buy a car, their ownership of it consists of 3 components:
- The time-based depreciation of the car, based on its age in months, as well as other non-usage based costs such as licence fees, interest etc. These happen if you drive or not.
- The usage-based costs of the car, based on miles or operating hours.
A robotaxi company also has all these costs (with less parking cost because they spend more time in circulation, working) but has to bill customers strictly by usage for their share of those time-based costs. The car owner, paying the monthly costs no matter how much they drive, is wasting their resource if they don't drive, and thus looks at the lower incremental cost in doing their math. This pushes them to do vacant car moves which would be wasteful with a taxi.
It could be that governments will wish to nudge this. One way they could do this is with road usage charges. As soon as there are road usage charges, they can discourage wasteful vacant operations, and bring the balance between use costs and ownership costs more in line with social goals.