My blue sky proposal in the Atlantic for replacing the subway trains with autonomous hoverboards lead to much debate and worse on the Internet.
Here are some responses to the more interesting questions and objections:
Is this Science Fiction or a Fantasy?
The Segway was unveiled in 2001. Hoverboards and electric scooters are everywhere. Google started testing their autonomous cars on roads in 2009. The iPhone, by comparison, appeared in public in 2007. These are all relatively old ideas.
What About Vehicle Width?
This is where we get big improvements. The track width is 12 feet and the airline seats are 18 inches wide. Some airlines are experimenting with 16.5 inch wide seats. Scooters and hoverboards aren’t very wide and they could ride three, four or maybe five abreast. They don’t need to ride in straight lines because different lanes could move at different speeds. Indeed, they would need to switch lanes when starting and stopping.
Turning one track into several lanes can dramatically improve performance when an accident blocks travel. It’s common for one stopped train to halt an entire line in one direction, creating backups that can take hours to clear. Thinner autonomous vehicles can zip around damage if the current track is split into multiple lanes. Of course every accident is different but stalling one lane doesn’t have to block all traffic.
The NYC Subway Isn’t Big Enough
Even though NYC is heavily populated and the tunnels seem small, there’s a surprisingly large amount of space in the system.
How much? There are about 1.76 billion rides on the system each year or an average of 4.76 million rides on an average day. There are 240 miles in the system and each car is about 10 feet wide. That’s about 12 million square feet in a rectangle that’s 10 feet by 240 miles. So if all 4.76 million riders jammed into the system at the same time-- and it often feels like they try-- everyone could all fit in one of these rectangles and get about 2.66 square feet a person, about what we’re lucky to get on rush hour in a modern subway car.
But the system has more room because there are tracks going in both directions and many of the major routes are four tracks wide with two used for express trains.
Thankfully everyone does not try to jam into the system at the same time and rush hour is spread out over 2 hours every morning and evening. If the commutes are about 30 minutes, then the density decreases by another factor of eight.
Of course many rides occur outside of rush hour. If 50% happen in the other 20 hours, that cuts the density in half again. This math doesn’t distinguish between the outer edges of the system and the center. It also treats weekends like weekdays. But it does give a rough idea about how much space there can be if we just spread out.
All of that adds up to at least 100 square foot of space per person during rush hour in the track real estate alone, about as much as some of the smallest houses on the market now. If that seems quite different from the amount of personal space you get on the train, it’s because the current system jams everyone into trains. The gaps between the trains can’t be used.
How Does This Translate Into Throughput?
Some like to measure how many people can move through a tunnel, an important statistic in a big city. The throughput depends upon how quickly the vehicles move and how many can fit into the track. The big advantage of competing fleets of autonomous vehicles is that they don’t need to be the same. Different vehicles of different sizes can travel together paying for time and space occupied in the tunnel.
But for simplicity, imagine identical hoverboards spaced with 10 feet between each other so a mile long line will have 528 vehicles. If the line moves at 15 mph, there will be 7290 people carried down the tunnel in one hour.
Slim vehicles like hoverboards or scooters can form thinner lines, allowing us to slice the tunnel into three, four or maybe five lanes. This would translate into 23760, 31680 or 39600 people per hour. Staggering the riders would increase the distance between vehicles.
A steady stream of autonomous SUVs like Google or Uber build could seat 4 passengers and take up the entire track. If they were spaced every 20 feet there would be 264 in a mile. If they ran at 30mph, they would also move 31680 people down the tunnel in an hour. If they could be made a bit thinner, there could be two lanes and that would double the throughput.
How Does This Compare?
R160a subway cars are said to hold a maximum of 200 people per car and there may be 10 cars in a train. If everything goes according to the official schedule, there are about 16 trains on the 1 track an hour during the morning commute. That translates into 32000 people per hour.
In practice, not every train has ten cars and delays can reduce the throughput. If it drops to ten trains per hour-- one every six minutes-- that’s about 20,000 passengers per hour. And then there are days that are really bad.
How is it possible that a steady stream of autonomous hoverboards going 15mph or autonomous SUVs going 30mph can carry the same amount as 16 trains? They don’t have to stop at each station.
What About the New Signalling Software
Many train fans love to talk about how new signalling software will make it possible to run 40 trains per hour, effectively bringing a new one into the station every 90 seconds. This doesn't make life easier for the passengers who need to move even faster, especially the handicapped, but it can increase the theoretical throughput. It's worth noting that this signalling software is essentially turning the trains into big autonomous vehicles.
Don’t Cars Take Up More Space?
Of course they do. Cars don’t pack people as densely as trains and that’s why it’s more comfortable to ride in a car seat than stand cheek to jowl in a train at rush hour.
A number of people have sent along a favorite image showing how a light rail train can pack together 200 people and take up less space than cars. It’s correct, but space is not throughput.
Even though cars are bigger, it doesn’t mean they are less efficient or have lower throughput. Trains must have large gaps between them when they stop at local stations and that’s why a steady stream of autonomous hoverboards or SUVs can move the same number of people through the tunnel as the 1 train.
It’s not enough to do the math and look at a static vehicle. You need to add in all of the space in between.
Why Do People Make This Claim?
The photo is very persuasive. I ran the three throughput scenarios abaove
So Autonomous Vehicles Won’t Reduce Capacity?
Why should they? They can move just as many people through the tunnel at 15mph as a subway train that constantly switches between very fast and a full stop. If we enhance protection, they can go even faster and carry even more.
Won’t Autonomous Cars Have Delays?
Of course. In an abstract sense, trains, cars and hoverboards are all just vehicles. The goal is to reduce the way that mishaps and problems affect others. Slicing the tunnel into multiple lanes adds options to fix problems. A blocked lane doesn’t have to halt the others.
Won’t Autonomous Vehicle Stop Too?
Yes, but we can reconfigure the stations with small side paths so they can pull out of the flow and decelerate.
Where will the vehicles be stored?
Many won’t be stored. They’ll just pick up another person and move on.
But the demand at rush hour means that some won’t be needed immediately. Perhaps these will be stored in the train yards. Perhaps on the platform waiting for the next customer. Perhaps in some of the corridors of the bigger stations. Perhaps they won’t stop but will travel without a rider, storing themselves in the traffic flow. Probably some combination of all of these.
I don’t think that big autonomous SUVs on the roads today will have much place in these tunnels. They take up too much space. But we could build nice, smaller two or four seat models that are just as comfortable and filled with real safety features like airbags.
Won’t the System Be Overrun at Rush Hour?
The current system doesn’t have a good way to adjust prices with demand. The DC Metro charges more at rush hour, but they only have two levels of prices. A sophisticated congestion pricing system could adjust prices according to demand in real time and this would almost certainly reward people who shift their work hours to save money.
What About the Other 20 Hours in the Day?
Continuous systems like autonomous vehicles can shine in the off-hours when trains are few and far between. It’s not uncommon to wait quite a few minutes late at night. Some lines have large gaps during rush hour. Autonomous vehicles can be ready immediately.
Congestion Prices Favors the Rich
Most of the people I know with tough jobs have to start early, return late or both. I think of congestion pricing as a tax on the bankers who want to work 9-5.
It’s common for people to call flat pricing “regressive” or “anti-progressive” because it takes a higher share of the income of those who are least able to pay it. In that sense, the one fare for all is anti-progressive or regressive pricing.
Aren’t Subways A Great Leveling Tool because Everyone Rides Them?
Forcing everyone to endure shared pain is not a fun model for civic organization. We’ve moved beyond the draft, for instance.The big advantage of having multiple service levels and shifting costs is that the formula can hide some cross subsidization. The people who want to travel at rush hour in fancier vehicles with better seats can be charged more than their fair share. The lowest grade service can be subsidized by the higher priced one. In most cases of differential pricing, the cheapest tiers are cheaper than they would be without the subsidy from the expensive tiers.
All but the most outrageously over-the-top cabs should still be in reach for most people who feel like splurging. Many of us enjoy so-called “affordable luxuries” like Starbucks coffee or iPhones occasionally. My cousins rented a limousine for my uncle’s funeral last month. It doesn’t mean they are rich. It’s just how they wanted to pay their respects. I believe it is a mistake to assume that only the rich will use the best vehicles and thus make it a rallying cry for class warfare. We all can benefit from choice.
Isn’t this Privatization?
I don’t use that word in the original article, although I understand how people made the connection given my affection for opening up the tunnels to multiple competing fleets. Consider Central Park. The city gives licenses to private vendors using a competitive process. It doesn’t mean that Central Park has been privatized.
Perhaps the city itself will run all of the different fleets. Or maybe just half. My infatuation is with the opportunity to nurture change, innovation and evolution. The ultimate ownership is not as important to me.
Don’t You Know All of the Details?
Some have mocked me for saying that I don’t know what shape or form the vehicles will take. It’s an easy joke and I’m happy to laugh along. But I believe this is a feature not a problem. We should be open to new opportunities and configurations that will come from many different corners of the the world. We don’t need to be limited to a standard gauge or a fixed schedule.
What about the Sexual Assault problems in well-packed subway cars?
Fans of subways often lionize subway lines in other cities where the trains run smoothly and the people don’t mind being squeezed in very tightly. While the engineering prowess is laudable, packed cars have downsides and occasionally some take advantage of it. Here’s one random snippet from the news. It’s easy to find others.
Sexual harassment cases in subway cars during commuting hours have risen by 26 percent over the past year, according to Seoul Metropolitan Police Agency. ...
Most of the offenders said they did it out of curiosity.
The Hoverboards Aren’t Fast Enough
The best subway cars can go 30 to 55 miles per hour-- until they have to stop and stop they often do. In practice, Google Maps estimates that it takes 30 minutes for the Number 1 train to cover the 6 miles from 96th Street to Chambers Street. That’s 12 mph-- on a good day. Google Maps also estimates 15 minutes to cover the 2.2 miles between Farragut North and Union Station in Washington, DC, about 8.8mph.
As they say in the ads, your mileage will vary because of people who jam the door, medical emergencies, over congestion, accidents and worse. In Washington DC, they sometimes switch to single tracks adding delays that can seem interminable.
The problem is that the subways run more efficiently in the off hours when the people don’t jam up the platforms or the doors. But the trains don’t run very often then and you’ll still need to factor in the amount of time you must wait for a train to arrive.
What About Express Trains?
The Express Train (#2) is supposed to take 20 minutes to get from 96th Street to Chambers Street according to Google Maps. That’s much faster, but it’s still only 18mph. Express trains only help the people who live and work near them. They are often less common, especially outside of rush hour, and some of the savings in ride time is wasted in waiting for them.
Speed Is Dangerous
We don’t know how fast the hoverboards will end up going, but they don’t need to go that fast to beat local trains. If you factor in the waiting time for a train to arrive in off hours, hoverboards often don’t need to go very fast at all.
Runners in track meets can go 15 mph over a mile and hit 20 miles per hour in sprints. Great marathon runners sustain 12mph. When the runners collide, they usually walk away. But accidents are unpredictable and people can crack their head if they fall the wrong way standing still.
This is not to say we should ignore the risk of collisions, only that a hoverboard moving at 15mph is very different from a train going at 40 to 55mph. The current trains are full of hard edges and there may not be a soft, padded surface anywhere. My grandmother spent several weeks in the hospital when her train on the Chicago Loop was hit from behind by another. She was slammed around and ended up under one of the seats.
The weight of a hefty train is responsible for the bulk of the kinetic energy that must go somewhere in a crash. If you get rid of much of the weight, you get rid of part of the problem.
If a slim protective frame and a bit of padding or air bags is added to a small autonomous vehicle that would be a big advance over the current trains where there are no seatbelts or much protection at all. The first generation of the Segway comes with a set of handles that offers some protection and stability but one of the newest is closer to a hoverboard.
Another option is to run fatter SUVs running at 30mph. The models on the road now have great airbags and crash protection. Not only would they get the riders to destination at 30mph instead of 12mph, they would offer dramatically safer rides than the trains. I think the best goal is something in between.
What About Other Advantages?
The autonomous vehicles don’t need to be limited to current tracks.The long networks of corridors in midtown are all fair game.
Nor do they need to be limited to the lowest levels. If the vehicles get fatter motors and better batteries, they can even carry the rider up to and down from street level.
The system can also add more entrances and exits. Big stores already have dedicated entrances and there’s no reason why the smaller ones or the apartment buildings can’t have their own too. More exits will speed time by getting rid of the walk from the subway entrance to your building.
What About the Streets?
Sure, they’re fair game too. Ideally, the hoverboards will zip up to street level and then travel the last few blocks to the destination.
The big advantage of starting with the subways is that it’s easy to limit the traffic to autonomous vehicles only. Everyone has a right to use the streets and that makes it much harder to program the cars.
What About those Who Are Less Mobile or Ride in Wheelchairs?
A scooter with a seat is like a wheel chair with a computer steering. The current subway system tries hard to accommodate those who don’t have the agility of youth, but there are limits to what the subway can provide, especially during rush hour. It’s hard to fit into the trains when they’re packed and the subway drivers are pushed to close the doors quickly to maintain throughput. Rush hour on the 4 train is no place for someone who needs a cane.
Allowing riders to board their own small vehicle at a more relaxed pace is one of the big advantages of this system.
What If You Just Called them Smaller, Thinner Subway Cars?
There are many Subway lovers out there and some of my biggest critics seems to work for the system itself. Instead of calling them autonomous hoverboards, let’s just call them tiny trains. Then we rip out the tracks and install four very thin gauge virtual tracks with lots of fast switches to make it easy to move around stalled “trains”. On these thin tracks would run very small, single person “subway cars”.
At some level of abstraction, subway cars and autonomous hoverboards are just vehicles, rectangles to be manipulated by some AI. The real key is finding a way to prevent a stalled vehicle from blocking every single vehicle behind it, something the subway cars tend to do. That’s why we make them thinner. Making them smaller and lighter saves energy and also makes it easier to deploy them on demand instead of making everyone wait.
Darkness
Many have pointed out that the subway tunnels would need some cleaning up. Certainly a bit of paint could really help. I originally thought that they should all be well-lighted, but now I’ve been thinking of the dark rides at Disneyworld and Universal Studios. When someone turns on the lights, they look very industrial and unaesthetic. They ask for a paint job. Maybe the right idea is to leave the tunnels dark and let each rider use a small light for reading. It works for Disney etc. Indeed Walt Disney designed the original People Mover to handle the job of subways.
And if you really want to dream, let’s rent the tunnels to Disney or Universal. They can put in amusement rides. They already charge $100++/day so people can wait 1-3 hours for a dark ride.(Voluntarily!) NYC could turn a profit if we mixed some entertainment in with the tunnels.
The point is to dream big about what we can do with this space, not cling to the old models.