Will Self-Driving Cars Solve Congestion?

Image from New York Times.

Conventional wisdom seems to be that self-driving cars will do a lot to alleviate congestion. They will be able to interact with each other and the environment so that they can space themselves closer together, detect and reroute around congestion, and not cause crashes (which accounts for about a quarter of the existing congestion). However, there are some factors that suggest that they may not completely solve the problem.

First a comment about the “rental vs. ownership” model. There are a lot of predictions that self-driving cars will act more like taxicabs, where you don’t own one, but punch a button on your smartphone and one shows up at your door.

Personally I’m skeptical.

1) There’s the whole “pride of ownership” thing, and being attached to your car. Of course maybe this will eventually die out with me and the rest of Gen-X.

2)What if the person that rode right before me has Ebola? Or a bad cold? And what’s that mystery stain?

3)What if I buy a couple of 50 pound bags of dog food and want to leave them in the trunk while I’m at work? Or if you just keep your bicycle in the back, as I do.

You can laugh at these scenarios, but people do think that way. There’s no strong rational reason for “rail bias” either, but it exists. There are already alternatives to owning your own car: taxis, ride-sharing, car-sharing, car rental, and transit. And there are drawbacks to each of these.  You’d think they’d be more popular if people really wanted to not own cars.

It’s also possible there might be a hybrid model, where a family owns the primary car but rents one as needed, or rents out their own car when they’re not using it.

But now lets look at the big reason why they might not fix congestion…

Self -Driving Cars will likely substantially increase Vehicular Miles Traveled.

People routinely mention that VMT is rising a lot slower in days gone by, or is even decreasing on a per capita basis. But that may not hold true in the future for a number of reasons. And with increased VMT (assuming highway expansion can’t keep up), comes increased congestion.

Here are some of the reasons:

1) Moving car storage around is going to add more miles

It seems a dream of urbanists to get rid of downtown parking garages. With self-driving cars, the cars could store themselves in an out-of-the-way location.

Fair enough, but that’s going to add miles traveled. And how close to downtown would massive car storage be palatable? They’re already trying to move the impound lot. Who’s going to want this facility in a developed area?

What’s more, suppose a downtown worker decides to send a car all the way back to Lake Elmo for a family member to use during the day? Or just because they doesn’t want to pay to park downtown? You’ve just doubled the miles traveled in a day.

It’s also possible you’d want to use your garage at home for a shop, rec room, or junk storage, and have your car park somewhere else.

2) People may choose to own more cars

Take a look at this 1950s Levittown ad. Space for one car. And then this typical Shakopee house. Notice how much more space for cars there is.

Levittown Ad
Typical Shakopee house

Right now in many cases we’ve reached a limit with one car per licensed driver. But what if you don’t need to be a licensed driver any more? Suppose Junior has a car to get to elementary school. Grandma has a car to get to her quilting club.

Alternatively, if the rental model comes to pass and people don’t own cars or own fewer cars, there’s still going to be  a lot of these extra trips, as well as driving from one fare to another.

3) People may increasingly choose longer commutes

I know “Millennials are choosing the city,” but not all of them are doing so. And not everyone moving into the area is a Millennial, and it’s possible preferences will change over time.

There’s been a desire for more space by people in the country ever since the resistance to the first anti-growth boundary, the Proclamation of 1763. The 1950s freeways and affordable houses just made possible what had been a long-standing desire (previously limited to streetcar suburbs). A couple of studies for one demographic group do not convince me things are going to to change in the long term. And it’s been decades since we’ve built a substantial number of affordable houses. The house in Shakopee above sells for more than triple what the Levittown house, in inflation adjusted dollars, cost.

The reasons for this suburban desire are complex, and might be worth their own post: zoning issues, builders figuring out they make more money building mansions and stack & packs, and consumers thinking they have to have granite because they saw it on TV, or thinking it’s child abuse for kids to share a bedroom.

But with no new supply of affordable houses, and lots of people wanting them, eventually the price of existing houses is going to rise to unaffordable levels, as it has in San Francisco and other places. For people that want houses, the choices would then be a long commute or settling for multi-family housing.

But what if you could take a nap or surf the internet during the commute?  A lot of us already spend several hours a day working at home, or on the computer, or on the phone. What if you could do that all during a commute?

The predicted 103,830 vehicles a day over the St. Croix Crossing in 2067 could actually happen. Maybe they even choose a school for their kids near work so they can have family time in the car. (Or what if even they choose a school a long ways away for their kids since it’s better and transportation is no longer an issue?)

4) There could be more delivery service

I think the idea is awesome that I could punch an order into my touchscreen in my car, and then pull up to Famous Dave’s and have food handed to me. (The kitchen would of course know when my car was due to arrive.) And then actually be able to eat something like ribs, even drinking a beer while in a car… it would be a welcome break from Taco Bell and Burger King.

But if driving is easier and cheaper, there may be more discretionary trips. Want a cheeseburger instead of ramen tonight? Order one, and the car will make a trip between Burger King and your house that you ordinary wouldn’t bother with.

5) The coming of Electric Cars

Even using gasoline, if energy costs remain the same or go up, with the above factors it’s likely VMT is going to go up. But something else is happening simultaneously…

Yes, the electric car. Right now a Leaf is impractical for anything but a second car for most families, and a Tesla is too expensive for most people.

But what if someday you could have an affordable car with a 200 mile range? I don’t know if it will happen or not, but there is a lot of motivation from different parties to try to make it happen. Electric cars are a lot cheaper than gasoline cars to operate, even more so that they don’t pay fuel taxes. Right now society has decided they’re fine with that. But at some point we’ll need to rethink transportation financing. And while we’re at it we might as well make users pay the full cost of the roads, most likely with a mileage based fee.

At $3 a gallon, a 30 mpg gasoline car costs 10 cents / mile in fuel costs, 1.6 cents of which is taxes. An electric car is typically 3.3 cents a mile, of which none is taxes. If you double the taxes to replace funding from general sources and add them to cost of an electric car, it’s still only 6.5 cents a mile, and the gasoline car goes to 11.6 cents. Going further, we could triple the tax and in turn eliminate the tab fees. This makes the heaviest users of the roads pay proportionately, but even then it’s only about 8 cents a mile. Probably still enough to induce a lot of extra travel  And to be fair,  we should have transit users pay the whole cost of their transportation choices too.

6) Shifting of Trips from Transit

But speaking of transit, remember the ridiculous proposal to just buy transit users cars? Well, that might not so ridiculous any more. Anyone that can physically ride in a bus can ride in a self-driving car. The energy cost would cheaper, so more people could afford it, or the cost or the government to provide it would be less. Or maybe, with a lot fewer reasons for people to take transit, we wouldn’t have to  provide services like the Gold Line. We could limit buses and trains to areas inside the beltway, by subsidizing the cost of renting or owing self-driving cars for the poor.

But wouldn’t that be just another form of transit? The lines get blurry!

It’s also interesting to think about what self-driving cars would  do to intercity transport. When I’m in Chicago I normally stay at a Holiday Inn Express in the northwestern suburbs. My house is in the southern suburbs here. To go by plane, I would drive to the airport, pay to park, then pay to rent a car in Chicago. What if I could leave at dusk, sleep, and then arrive in the morning with my own car? And with an electric car the cost being less? I might travel a lot more for pizza. But if I’m going to take regular trips of that distance I want something comfortable.

There May be a Focus on Comfort, Rather than Efficiency

We’ve all seen this cute Google Self-Driving car. You could fit a lot of those on I-94, right?

Well, you can buy a conventional car that looks like that today.

There seems to be a complete and utter lack of interest in the US. The Smart Fortwo sold 9264 in 2013, compared to 360,089 Honda Accords. You could make the case that if the rental model of self-driving cars comes to pass that people could take a Smart Fortwo to their job in the city, and use the Ford F-150 for towing the boat to the lake on the weekend. But right now there’s already that market for “2nd cars”. People could have a pickup for the weekends and one daily driver, and a city car for the second daily driver, but they don’t.

Instead, here’s another take on what a self-driving car could look like, the Mercedes concept:

Just a little bit bigger. If people increasingly choose two hour commutes to save on housing costs or to get more space, and no longer needed to drive, they’re going to want more space to be comfortable. So you might see recline-flat seats, big screen TVs, and maybe even RV-like amenities like lavatories and kitchenettes.

A car being too big for people to be comfortable driving is no longer going to be an issue. And the cars will undoubtedly be programmed to increase comfort by gentle acceleration and stops. Everyone who’s been behind a semi truck “gently accelerating” knows what it can do to traffic.

Ultimately I look forward to self-driving cars. I figure they’ll be ready for prime time when it’s about time for me to surrender my “manual car” license, and thus I won’t loose my freedom. But I don’t think they’ll won’t solve congestion. They’ll just make it matter less.

About Monte Castleman

Monte is a long time "roadgeek" who lives in Bloomington. He's interested in all aspects of roads and design, but particularly traffic signals, major bridges, and lighting. He works as an insurance adjuster, and likes to collect maps and traffic signals, travel, recreational bicycling, and visiting amusement parks.