Robocars will make traffic worse before it gets better


This blog, and many other sites, paint a very positive picture of the robocar future. And it is positive, but far from perfect. One problem I worry about in the short term is the way robocars are going to make traffic worse before they get a chance to make it better.

The goal of all robocars is to make car travel more pleasant and convenient, and eventually cheaper. You can't make something better and cheaper without increasing demand for it, and that means more traffic.

This is particularly true for the early-generation pre-robocar vehicles in the plans of many major automakers. One of the first products these companies have released is sometimes called the "traffic jam assist." This is a self-driving system that only works at low speed in a traffic jam.

Turns out that's easy to do, effectively a solved problem. Low speed is inherently easier, and the highway is a simple driving environment without pedestrians, cyclists, intersections or cars going the other way. When you are boxed in with other cars in a jam, all you have to do is go with the flow. The other cars tell you where you need to go. Sometimes it can be complex when you get to whatever is blocking the road to cause the jam, but handoff to a human at low speeds is also fairly doable.

These products will be widely available soon, and they will make traffic jams much more pleasant. Which means there might be more of them.

I don't have a 9 to 5 job, so I avoid travel in rush hour when I can. If somebody suggests we meet somewhere at 9am, I try to push it to 9:30 or 10. If I had a traffic jam assist car, I would be more willing to take the meeting at 9. When on the way, if I encountered a traffic jam, I would just think, "Ah, I can get some email done."

After the traffic jam assist systems come the highway systems which allow you to take your eyes off the road for an extended time. They arrive pretty soon, too. These will encourage slightly longer commutes. That means more traffic, and also changes to real estate values. The corporate-run commuter buses from Google, Yahoo and many other tech companies in the SF Bay Area have already done that, making people decide they want to live in San Francisco and work an hour's bus ride away in Silicon Valley. The buses don't make traffic worse, but those doing this in private cars will.

Is it all doom?

Fortunately, some factors will counter a general trend to worse traffic, particularly as full real robocars arrive, the ones that can come unmanned to pick you up and drop you off.

  • As robocars reduce accident levels, that will reduce one of the major causes of traffic congestion.
  • Robocars don't need to slow down and stare at accidents or other unusual things on the road, which also causes congestion.
  • Robocars won't overcompensate on "sags" (dips) in the road. This overcompensation on sags is the cause of almost half the traffic congestion on Japanese highways
  • Robocars look like they'll be mainly electric. That doesn't do much about traffic, but it does help with emissions.
  • Short-haul "last mile" robocars can actually make the use of trains, buses and carpools vastly more convenient.
  • Having only a few cars which drive more regularly, even something as simple as a good quality adaptive cruise control, actually does a lot to reduce congestion.
  • The rise of single person half-width vehicles promises a capacity increase, since when two find one another on the road, they can share the lane.
  • While it won't happen in the early days, eventually robocars will follow the car in front of them with a shorter gap if they have a faster reaction time. This increases highway capacity.
  • Early robocars won't generate a lot of carpooling, but it will pick up fairly soon (see below.)

What not to worry about

There are a few nightmare situations people have talked about that probably won't happen. Today, a lot of urban driving involves hunting for parking. If we do things right, robocars won't ever hunt for parking. They (and you) will be able to make an online query for available space at the best price and go directly do it. But they'll do that after they drop you off, and they don't need to park super close to your destination they way you need to. To incorporate city spaces into this market, a technology upgrade will be needed, and that may take some time, but private spaces can get in the game quickly.

What also won't happen is people telling their car to drive around rather than park, to save money. Operating a car today costs about $20/hour, which is vastly more than any hourly priced parking, so nobody is going to do that to save money unless there is literally no parking for many miles. (Yes, there are parking lots that cost more than $20, but that's because they sell you many hours or a whole day and don't want a lot of in and out traffic. Robocars will be the most polite parking customers around, hiding valet-style at the back of the lot and leaving when you tell them.)

Another common worry is that people will send their cars on long errands unmanned. That mom might take the car downtown, and send it all the way back for dad to do a later commute, then back to pickup the kids at school. While that's not impossible, it's actually not going to be the cheap or efficient thing to do. Thanks to robotaxis, we're going to start thinking of cars as devices that wear out by the mile, not by the year, and all their costs will be by the mile except parking and $2 of financing per day. All this unmanned operation will almost double the cost of the car, and the use of robotic taxi services (Robocar Uber) will be a much better deal.

There will be empty car moves, of course. But it should not amount to more than 15% of total miles. In New York, taxis are vacant of a passenger for 38% of miles, but that's because they cruise around all day looking for fares. When you only move when summoned, the rate is much better.

And then it gets better

After this "winter" of increased traffic congestion, the outlook gets better. Aside from the factors listed above, in the long term we get the potential for several big things to increase road capacity.

The earliest is dynamic carpooling, as you see with services like UberPool and LyftLines. After all, if you look at a rush-hour highway, you see that most of the seats going by are empty. Tools which can fill these seats can increase the capacity of the roads close to three times just with the cars that are moving today.

The next is advanced robocar transit. The ability to make an ad-hoc, on-demand transit system that combines vans and buses with last mile single person vehicles in theory allows almost arbitrary capacity on the roads. At peak hours, heavy use of vans and buses to carry people on the common segments of their routes could result in a 10-fold (or even more) increase in capacity, which is more than enough to handle our needs for decades to come.

Next after that is dynamic adaptation of roads. In a system where cities can change the direction of roads on demand, you can get more than a doubling of capacity when you combine it with repurposing of street parking. On key routes, street parking can be reserved only to robocars prior to rush hour, and then those cars can be told they must leave when rush hour begins. (Chances are they want to leave to serve passengers anyway.) Now your road has seriously increased capacity, and if it's also converted to one-way in the peak direction, you could almost quadruple it.

The final step does not directly involve robocars, since all cars must have a smartphone and participate for it to work. This is the use of smart, internet based road metering. With complete metering, you never get more cars trying to use a road segment than it has capacity to handle, and so you very rarely get traffic congestion. You also don't get induced demand that is greater than the capacity, solving the bane of transportation planners.


The manual version of last mile services feeding longer distance (still intra city) public transport works tolerably well in Jakarta, which has poor roading, little rail and of course chronic congestion.
It might make sense for a local body to fund a free robotaxi service for just this function as a means of reducing the need for roading investment. It would also have the advantage of steering robocar adoption towards the service model and away from private ownership.

It is very common for transit planners to think of robotaxis as a solution for their last mile problem. And they can be, but this is very narrow thinking constrained by the old way of doing things. And they will be "last 20 mile" solutions for long-haul travel by air, rail and possibly some day hyperloop.

But the broad mistake here is that large vehicle transportation (ie. rail and even bus) is not nearly as efficient as people imagine, and in order to get a large group to all travel together over a long distance you must have a route and a schedule, rather than letting people travel when they want. That means wait times and inconvenience. Smaller vehicle transportation (vans, full cars, minibus) offers travel without routes or schedules, according to real time demand from passengers.

Smaller vehicles are a little less efficient, but there are diminishing returns. Worse though, once the large vehicles are on a schedule, it means they run even when the load is low, making them quite inefficient. The packed train at rush hour is efficient, but the 1/3rd full one off-peak is quite wasteful. One answer is to use the large vehicles only at rush hour but that is also not efficient as you build a big system to only run a few hours a day.

This leaves one advantage for large vehicle transit, which is that you can justify dedicated right-of-way to get around traffic. But if we can fix traffic with metering, that advantage becomes a waste -- the train tracks have a train on them only every 30 minutes in many cases, while the roads can have a van every second.

I agree about the load factor issue with mass transit, though I expect that robotaxis will also suffer from this during peak times while we continue to have a large influx to the city in the morning and matching return exodus.
As for train tracks, I cannot see why we wouldn't concrete/tarseal around the tracks and allow robocars/robovans to share the corridor with trains.
Surely a signalling system can be created which would allow this.

Load factor should be excellent at rush hour -- easy to find people sharing a large segment of their journey. Are you referring to the potential of empty vehicles making return trips to bring more people in the commute direction? That's just an economic question -- is it more efficient to have empty vehicles do the return trip or just to have (and store) more vehicles in the overall fleet? This will depend on the length of the return leg to some extent. Of course vehicles in the anticommute direction do not cause much congestion, but they do use energy and put wear on the vehicle.

You're right I didn't express it clearly.
As you stated load factor will be great for the inward journey and poor for the return.
I think at rush hour at least the cars will make the return trip as it would be unlikely that the cost of the journey is higher than that of having spare capacity.

If you do the simplest form of the math. Let's say a vehicle can make 3 commute trips and 2 anti-commute trips per rush hour, over say, a 10 mile trip. So that's 40% empty miles or more. Let's say storage (parking) is $2/day and travel is 30 cents/mile and financing is $2/day (this is a low cost single person vehicle.)

So the roundtrip method makes 6 loaded trips, travels 100 miles, daily cost of $34 for six loaded trips or $5.66 per trip. The "extra vehicles" method does just 2 trips, 20 miles, daily cost of $10, or $5 per trip. Slightly cheaper.

In this version, it's close to a wash, and changes to the price of all factors can move it one way or another. The roundtrip car wears out 5x as fast, which is actually good, since it's going obsolete for technological reasons too. Financing cost will be fixed, though an efficient taxi that spends the day giving out rides may need less parking time. Parking is generally cheap as it is done at the cheapest available spot within short range -- see my articles on parking for details.

>>While it won't happen in the early days, eventually robocars will follow the car in front of them with a shorter gap if they have a faster reaction time. This increases highway capacity

When the vehicles at highway speeds are following closely enough to eliminate rear vortex drag, close-follow also increases fuel economy for every vehicle closely following, while also increasing the fuel efficiency of the lead vehicle. As more vehicles closely caravan, their fuel efficiency continues to increase for quite awhile.

The fuel savings are there, and yes, for the lead vehicle too, but not actually as much as people hope -- 10-20% is not uncommon, sometimes even less. As such the real benefit is increased highway capacity. However, there are costs. An increase in risk (particularly with longer convoys,) the blocking of the lane, the cars that try to push into the gaps not understanding what they are, and the stone chips that fly up from the forward vehicles, destroying the finish, windshields and even radiators of following cars.

"Operating a car today costs about $20/hour"

You know, you keep saying this, and it's never true, and it won't be. You're getting the wrong numbers and calculating them the wrong way.

Let's assume. So you're downtown pitching Juicero 2 to some VC bro whose phone still uses the default sound for texts. The pitch is an hour and the average speed is fifteen miles an hour, so your car will travel fifteen miles.

Insurance, if offered on a per-mile basis, is advertised as three to five cents per mile. So that's $0.65 for the cost of insurance.

"but, wait, what about the basic cost of the policy--" well, you'd pay that basic cost whether the car were driving around or sitting in a garage, wouldn't you? So it's not part of the calculation here.

The energy cost of driving an electric car is subject to vehicle efficiency and the cost you pay to charge it; rolling with 2 miles per kilowatt-hour (low efficiency) and $0.25 per kW/h (moderate cost) gives us twelve cents per mile, or $1.80 for fifteen miles.

Maintenance, on the other hand, can be calculated on an overall-lifetime per-mile cost. Assuming a 75k-mile cost of $1200, 30k-mile interval cost of $250, and 3k-mile interval cost of $50, and a service life of 150k miles, we get a total cost of $6150 and a per-mile cost of $.041, giving a cost for those fifteen miles of $.615.

So we put together maintenance, insurance, and energy costs and find that driving around for one hour at fifteen miles an hour costs...three dollars. Not twenty. If you want to complain that I've under-booked this or that, fine, double my number, triple it. You're still under ten dollars to have your car drive around the city for an hour. And if the car goes slower than fifteen miles an hour--driving fewer miles--then the cost goes down similarly.

"Oh, but you forgot the mortgage, the license, the registration--" again, you'd pay that anyway even if the car were in a garage. Those terms appear on both sides of the equation and drop out.

The industry tends to use cost per mile, so getting per hour figures is difficult. The real costs vary and depend on both. Cost per mile is clearly wrong -- at highway speed, your engine is revving smoothly and cool, gas mileage is superior, accident risk per mile is less. At city speed, there is constant rev up, braking and slow down, risk per mile is high. So while both miles and hours are a proxy, I think hours do better. If you wanted a better measure of car age, it might be total revolutions of the engine, with total brake force and many other things. In boats and planes, age is measured exclusively in hours.

As noted, electric cars are different. They actually can get better mileage at low speeds. But right now the biggest depreciation of an electric car when you drive it is battery wear. Though Tesla is showing that it may be possible to reduce battery wear a lot. But it's still much more than the cost of the electricity. The big killer for the electric car is that pointless driving costs range, and range is the most expensive part of an electric car. The cost is entirely dominated by how much range you want the car to have. Set it to drive for no reason and it's burning up its range just before you use it, unless you can time it to recharge just before you want it.

Insurance today is sold by the year, but that's also artificial, and the reality is it's very much mile or time based. Many want to change it to be that way. And for self-insured self-driving cars, there will be no illusion about where the real risk is and where the costs come from.

But whether you want to price it per mile or per hour, the cost of cruising still is vastly more than what the cost of parking will be. Today, parking's price is very artificial too, because there is very limited competition in parking. People must park close to their destination, they do not have another easy option. So they can't comparison shop 200,000 parking spots to see who is offering out the best prices right now. Their car can't switch spots for them if the price changes during the wait. And their cars don't auto valet park the back of the lot in the cheapest spot within miles. (To add to this, people who know what direction they are going when they leave can have the car park many miles away along that path, and if they need it on short notice, just hop in a cheap taxi that takes them to meet their owned car. The cheap taxi is only going to drive for a few minutes, its cost is much less than having the car cruise for hours.)

Parking will be pennies per hour, at least until most of the parking lots get torn down. Cruising will cost dollars per hour. It will also be antisocial of course, and if people still do it in spite of the waste, a policy solution may be applied.

"Parking will be pennies per hour"

uhhh, not in any city I've ever been in, and there's certainly no reason to expect that to change.

Heck, if you're suggesting that the demand in edge-of-city parking spaces will increase as robocars find them and park in them, then why would the cost to park there go down?

You might see the cost of in-town parking decrease, because (as you point out) the robocars of people who want to park will drive out of the city. But that won't be a change in the overall parking ecosystem, that'll just be spreading it out. It certainly won't be "pennies to park" level.

Also I like the way that you sniff about "low speeds are much less efficient for driving!" and then say "for electric cars, low speeds are more efficient". I don't even have to argue, I just have to stand here and watch a watermelon eat itself.

"right now the biggest depreciation of an electric car when you drive it is battery wear."

Do you have some numbers for actual battery wear across the deployed EV fleet? If you're going to make quantitative assertions then you need to bring in some quantities to back them up. If you're saying "it costs more to drive around than to park", that's a factual assertion based on a calculation. That needs numbers.

"the cost of cruising still is vastly more than what the cost of parking will be. "

Ah-heh. "I'm right, so long as a bunch of stuff changes to make me be right" isn't really a meaningful argument.

I outline this in The Incredible cheapness of being parked.

As for electric vehicle depreciation, this is something we are still learning about. Tesla is reporting some pretty good numbers, other vendors not as much. But nowhere have I seen numbers that are less than the 3 cents/mile price of the electricity in typical electric vehicles, and the <1 cent/mile price of the electricity in a small single-person electric vehicle.

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