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Comment by djsumdog | Hacker News Reader

Autonomous cars are a very difficult problem, more than I think most people anticipate. There's been a lot of tax breaks/money that goes into these programs too, and that's the tragic thing, since that funding should be going to known solutions: public transportation (trains, trams and express buses).

Even if you had a full-autonomous only Interstate where each car could be fully loaded and ride bumper-bumper at over 100kph, it wouldn't even begin reach the carrying capacity of currently existing fully autonomous subways systems like those in Singapore.

https://penguindreams.org/blog/self-driving-cars-will-not-so...

These driverless cars would be great in Europe where they can solve the last leg problems in countries that already have strong public transport infrastructure. In places like America, the existing infrastructure has a long way to go before autonomous cars won't lead to the same gridlock as normal cars .. and an even longer way to go before they're ready for mass consumption.

View on HN

Most of the money spent on autonomous autos is being spent on research, while most of the money spent on public transportation solves a select few routes. Solving auto driving essentially solves it everywhere. Here in Seattle we are spending over 50 billion to put in a couple of light rails, and it won't even be close to being enough public transportation. The money the government is putting in self driving pales in comparison to what is being put into public transportation. Even with public transportation, you still need self driving cars. Look at nyc or London, hey both have great subay systems and yet have some of the worst traffic. Not to mention self driving technologies can help public transportation, freight deliveries, as well as others.

Seattle's ST3 is a massive project and it will solve a lot of problems! The extension goes all the way to the Redmond tech center and the other extension will eventually make it to Everett, meaning there will finally be a train that runs all the time instead of just a few times per day M-F and for select sport events.

There are so many people who cannot afford housing anywhere near Seattle and they are the runs who run your Wal-greens and Starbucks. They have to sit in traffic on I-5 or wait for express buses. This will be a big step up and it's only a start. Seattle needed ST3 a decade ago, and it's going to have a way bigger impact that you think.

New York and London have okay subways. Tokyo has a great subway and incredibly light traffic.

I’d argue that Tokyo’s PT is so good that the last mile is mostly your feet if you’re able bodied. Autonomous cars is mostly something that makes sense in less densely populated places IMO. Which does include most of the US, but frankly I doubt car sharing will make a big impact there soon.

Everywhere and everyone is different, obviously, but I would love to see autonomous electric vehicles become our future. I really don't care for public transportation, I find it uncomfortable in many ways, and I don't see any way that it will ever not be about half the speed of a private point-to-point transport.

So a highway filled with self driving cars zipping along bumper to bumper may not technically be able to carry as much as a fully loaded subway train, but it's so much more useful. Take away the casualties and pollution, and it's as close to perfect as we are likely to get.

> and I don't see any way that it will ever not be about half the speed of a private point-to-point transport.

Subways / trains in Tokyo are faster than driving, same in London.

No stop lights, no intersections, no delays on the road.

Buses aren't faster, but once you go underground, the speed improves dramatically. Even if there is a 2 minute stop once every mile, that is still less time waiting than comparable stop lights in a car.

As far as I can tell, that's only true in fairly unique situations, though, in the super-cities. I live in a decently sized city (metro population of perhaps 3 million people, around 25th in the US I believe) with a transit system mostly regarded as 'pretty good' (but no subway, just light rail and buses) and it would be rare even at rush hour for a car not to be faster. Usually signficantly so.

I think what it comes down to is that if you have a subway system, that will probably beat cars, in the limited area it serves. Once you have to do transfers to buses, it gets much slower. In the places I've visited with subway systems (SF, DC primarily) this is definitely the case.

The US, even cities with “pretty good” transit by local standards, had appallingly bad transit and car-optimized cities.

Here's an interesting overview of US cities mass transit by an urban planner from Houston (an admittedly vary car centric place.) https://www.vox.com/the-goods/2018/12/7/18131132/public-tran...

US transit is heavily optimized for cars, even in places with pretty good mass transit. Don't let your personal experience with US metros color your expectations for what public transit can be.

> with a transit system mostly regarded as 'pretty good'

That's probably US bias, because as far as I can tell by reporting US public transport is generally very bad and far worse in big cities compared to much smaller cities elsewhere.

How about once you factor in time to walk to and from the station.

You have to count that against time spent at the gym, not against commute times. :)

Doing this in chicago winter sucks. I did that for many years and now I drive.

Still quicker in London, doubly so if you're including walking to and from the car park.

Can you explain to me how it's more useful than a train that carries more people with less energy?

Because, to me, it sounds like you just don't want to be uncomfortable, and that's fine, nobody does, but it doesn't make something more useful.

How do I get from my house to the train? Do I have to make transfers? How long will they take? What if I have to carry groceries, or take young children with me, or my elderly grandma?

If I have a car, I load everyone and everything up, and we go. We get to our destination and unload, ta-da! Is this not an order of magnitude more useful than taking a train?

Sometimes I think HN is filled with young people with uncomplicated lives :).

>Sometimes I think HN is filled with young people with uncomplicated lives :).

No, if these are big issues for you, you likely live in an American low density area where public transportation is scarce. In large metropolitan areas (which is after all, where most of the world already lives, and will live), getting on and off public transport is usually not a problem.

I have relocated to Tokyo for example about a year ago, and for me, a trip to the grocery store is usually done by foot (same is true for other appliances), and multiple forms of public transport are in walking distance.

I live in a city with about 700,000 residents inside the official limits, and 3,000,000 residents in the metro. The nearest bus stop is approximately a quarter mile away.

With all due respect, the number of people who live in cities as dense as Tokyo are the minority, most of us don't.

No offense but if you think walking a quarter mile is a hindrance to access public transport then the car culture has done even more damage than I thought.

On the contrary, I think a quarter mile is perfectly reasonable for a public transit stop in my city. Sorry to suggest otherwise.

However, when I think about loading up my young children with all of their stuff, loading me up with everything I need, etc, and then dragging that down the street a quarter mile, then waiting for the bus, boarding it, riding to the transit center, transferring, riding another bus to the light rail station, riding that downtown, and then doing it all again the other direction... well, I'm pretty confident in my original point that the car is a hell of a lot more useful. Sure, you can exist with only the public transport option, but I was not asserting otherwise. But a lot of people on HN seem to think that not only is it possible, but that it is the superior choice.

So, no offense taken, in fact I appreciate you affirming my original comment about so many folks on HN commenting from the viewpoint of someone with a young, uncomplicated life :-).

Many people with kids do what you describe in cities. It's far better for everyone, and even if it's not the superior choice for an individual (though I'd contend it is when you adjust your lifestyle), it is the superior choice for everyone together as it avoids pollution, traffic gridlock and huge fuel inefficiencies.

As it is those with cars push off these negative externalities onto those who choose not to have them, or can't afford them. So your comfort does have a cost, which you don't pay directly.

Perhaps I'm sheltered or naive, but it seems to me that in a well designed system you shouldn't really have to take two bus connections to get to your nearest light rail station. More like zero, or one max if you live on the outskirts. This is how it is in London, and while I realize that's not a typically sized city, it's not unusually dense either. I think that kind of system is possible anywhere, it just requires motivation.

¼ mi is a 5min walk. Often you need to walk as far or further to and from the parked car. I literally yesterday just took 2 kids, a toddler and a baby, on a multi connection trip, and it's easy, simple, and less stressful then driving.

Also, tour last paragraph just makes you sound pompous and liek you have no intention of having a discussion but instead only wanting to put others with a different point of view down.

I think you're making it more complicated than it is in many places. In many you'd need not get in a bus at all, because the rail stations are dense enough to always be a couple blocks away. That requires having more than just 1 train line though, which is only really true in NYC (and maybe Chicago? You have to squint really hard for but to be the case even in sf) if you're looking in the us.

Nailed it.

A quarter mile to the closest route typically means a far more complex combination of transfers, each with its own delays, to actually get to your destination of choice.

A quarter of a mile is a long distance for a bus stop in a city with good transport. But sounds like your city doesn’t have enough transport density. Tokyo is pretty dense but its still not abnormal.

> What if I have to carry groceries, or take young children with me,

I exclusively use public transport, and regularly do both of these without any problems.

Because trains don't go door to door. Obviously.

Except in lucky places with great underground railways you basically have awkward last-mile journeys where you have to take a taxi or hit a car or take a bus and that adds a lot of time to the journey.

It would be great if there were trains everywhere but frankly that's even harder than making a reliable driverless car.

Which is why driverless cars are great for bringing people from and to public transport. They are a great ingredient for improving public transport, but they don't replace it (at least as soon as road capacity becomes an issue).

I doubt that a train is significantly more energy efficient than an electric car with 3-4 people in it. Most people will probably use pool type autonomous cars which get you to your destination door to door much faster than trains.

Trains can fit far more people than cars.

Being more comfortable is useful to me.

Trains can be extremely comfortable, actually. You can have things like food/drink service on them, not to mention WiFi.

The lack of comfort people refer to usually involves the other passengers, not the amenities. But everyone knows you're not supposed to talk specifically about that aspect of public transportation.

Ha, I will! I once had a guy behind me on the train whip out his penis and pee on the floor. Looked right at me in the reflection of the window as he did it. He wasn't even crazy, either, as far as I could tell, just antisocial.

And yes, before you say it, that isn't an everyday occurrence. But jackasses refusing to take their bag off the seat so you can sit down is. As are people who can't be bothered to take a shower, or think that cologne will make up for it. The list goes on. Many people are just unpleasant to be around, and I don't see any problem with that observation.

For me, public transit comfort comes down to a couple things. First, the hard plastic seats make my butt hurt, and standing makes my left foot ache. Sorry, I'm getting old :). Second, the 2x time it takes to get anywhere means I'm on that terrible seat for even longer. And third, because yes, it's absolutely true, I find that perhaps one in ten people is unpleasant enough that I want to be out of visual and/or aromatic range.

> First, the hard plastic seats make my butt hurt,

Yeah, same for me. And I've heard that the ~80s crop of NYC subway cars were made in Japan. Except there, they have upholstered seats. But that wouldn't work out well in NYC, so they got hard plastic. But on the other hand, the oldest LIRR cars (refurbished for the 1966 World's Fair) had upholstered seats, and they were ~OK.

Some Finnish trains have play-areas for children on them. I was pleasantly surprised the last time I rode a train with my 1.5 year old child. He had a lot of fun going up and down the slide, sitting in the toy-train (on a train!) and reading books in the "library".

Never in my life have I experienced a puddle of urine in my personal vehicle. This happens about 5% of the time with my city’s public transport.

Similarly, never have I been given religious literature or panhandled. This happens about 90% of the time.

Sounds like you just have poor public transport. It doesn't have to be that way, and I've never experienced anything like it in Europe.

Yes,precisely. I found Vienna and Tokyo’s subway pretty immaculate. But London, Paris, Bilbao, Amsterdam all had some experiences similar to my other post. Much smaller sample so hard to say how frequently it occurs in any useful way.

Or maybe a dysfunctional society :(

5% is a staggering number! I rode the trains for four and a half years in NYC and just avoided the empty cars and never had too many issues.

Also people seem to focus exclusively on the negative interactions which is a very human thing to do, but this discounts the positive interactions.

It can be really nice seeing people offer their seats to the elderly, or kids meeting and playing, or the occasional furry companion in a cute bag.

But I enjoy people watching in general. It can be neat to try to imagine a persons world and how it looks.

I still think public transport is a net positive. But completely understand the allure of my own car. Or an Uber managed self driver where each rider rates the past.

My car has WiFi, and it is not even automated yet. And food & drink are perfectly feasible as well, remember we're talking about automated cars now. All kinds of options suddenly make sense when you don't have to worry about the chore of driving.

I admit that I'm only doing rough math in my head, but it seems to me that cars bumper to bumper at 100kpm is definitely going to have a greater carrying capacity than intermittent larger vehicles that stop a lot. (Or at least a similar magnitude)

I don't expect self-driving cars to drive much more densely than current cars, though, because all or almost all the same reasons we drive with separation still apply for self-driving cars. Where you might think you get some advantages, they will also have disadvantages, too, like being able to compute exactly how risky their behaviors are. People making the cars and writing the car software aren't going to want to stand in court and explain why their car crashed the 50-car dense train because their car software left no possibility of the brakes going out at that exact moment (i.e., no previous sign of brake failure), and caused a huge crash because none of the cars had any buffer for failure.

Personally I expect self-driving cars to drive a great deal more conservatively than humans as a result, and I think self-driving cars are going to end up demanding a lot more space and buffer on the freeways. And if they don't at first, one day you'll way up and they suddenly all will, because somebody won some lawsuit and a software update was pushed overnight to double the buffers.

The fundamental difference between human and automated drivers is that humans aren't going to get any better. Software based systems will get to human level then continue to improve to the limits of computing and physics, which is certainly better than humans.

And we haven't even considered networking. When the cars are all talking to each and routed together then it's fundamentally a single machine.

The laws and systems will evolve with capabilities rather than getting stuck on supporting the earliest generation of self driving vehicles and norms.

I tend to agree, I expect that as a practical matter autonomous cars will be conservatively driven, e.g. with large buffer zones, gentle acceleration, safety-above-all-else.

I think other drivers will adapt to this and start taking advantage. Think of what happens when you leave a legal following distance in front of you now, in traffic. Now imagine an autonomous car in the same situation. It would probably end up stopped.

I'm not sure this is a bad thing. Often times, traffic jams are caused by not enough spacing, or unobservant drivers resulting in sudden breaking, and a knock-on effect. Would need to simulate to confirm, but I suspect that more vehicles giving enough stopping distance, and accelerating smoothly would improve traffic flow, even with the addition of more defector (defective?) drivers.

Might as well imagine autonomous-only lanes while we're speculating.

The primary reason we drive with separation is our reaction time. Computers can react must faster. In addition they can actually talk to the cars around them. They could literally form a train. We won't switch to self driving cars until they can drive better than humans. If they have to leave a larger buffer, then the work isn't done.

I don't think it applies that easily.

There's still a chance an automated car encounters something that couldn't be spotted / reacted to. For example a deer/kangaroo/whatever jumping right in front of it. If the cars keep their distance, only the first one crashes. If they form a minimum-spacing train, the only message they can send to the following ones is "you're screwed now".

A deer would be unlikely to jump into a train of cars. They usually get caught by cars that have space in front of them. I know you are just giving a single example, but anything that applies to an actual train would apply to a virtual train as well. I don't understand why not having a physical latch between cars makes any real difference.

A deer doesn't affect a real train that much due to the mass difference. In case of cars though they cause serious damage. If the following cars don't keep a distance they end up immediately crashing into the first one, multiplying the damage.

I don't have much experience with deer behaviour, but kangaroos will happily jump right into anything moving. They will even hit the side of your car sometimes (which they should've obviously seen coming)

The major reason we drive with the space between cars that we do is human reaction time. That is at least an order of magnitude better in autonomous cars.

Cars driving bumper-to-bumper at 100km/h would be extraordinarily unsafe.

Anecdotally I commute to work because it's faster and much less stressful. Granted I do need to cover the first leg by car due to the public transport in my area, but the little bit of walking and the free time I get in the train are so much better than sitting alone in city traffic.

Sounds like a friend of mine who loves the time to read a book or work on his laptop.

I look out the window of the train, though, because otherwise I get motion sick. It's lost time to me.

> I don't see any way that it will ever not be about half the speed of a private point-to-point transport.

Private point-to-point loses out mostly for long-distance already, short-distance currently either allows last-mile, station overhead, and related concerns to big down shared transportation or suffers from sharing infrastructure optimized for private point-to-point.

Ubiquitous automated (on-demand, not personal cars actually make the station problem easier, since you need less parking at stations, making station footprints smaller, and reducing delay from arrival at station to boarding.

They could also merge with buses: instead of fixed routes and schedules, vehicle sizes and routing are demand driven for efficiency (perhaps allowing you to pay a premium to guarantee a dedicated vehicle for your party.)

I would be comfortable saying that subways and above (e.g. high speed rail, airplanes) are a special case of public transport that will always make sense and will nearly always beat out a car for transit time.

Aside from that, I agree with what appears to be your premise -- that we could invent public transport devices that mitigate and perhaps mostly erase the advantage of the car.

But then I'd ask ... why? Why are we supposed to hate cars? It's okay to like scooters and bikes, but nothing larger until we get to a bus? I imagine a future with all sorts of automated cars that never get into an accident and roll silently along emitting not a whiff of noxious fumes, while being big enough to carry just the right amount. If nobody needs to own their own car, then they can call a car that is sized for their exact needs. One passenger or ten. They efficiently get to exactly where they are going in the minimum time possible with minimum effort. What a dream!

> I agree with what appears to be your premise -- that we could invent public transport devices that mitigate and perhaps mostly erase the advantage of the car.

That's not quite my premise.

Rather, it is that shared self-driving automobiles (cars through vans through buses) with centralized automated dispatch are the missing element of the mix of public transport devices that, alongside existing options, does that.

> Why are we supposed to hate cars?

Recognizing that public transport has social benefits does not require hating privately owned cars, much less cars more generally.

> It's okay to like scooters and bikes, but nothing larger until we get to a bus?

Size has nothing to do with anything (well, it has to do.with efficiency for long-distance transport.)

Cars take up massive amounts of public space. Look at a car dependent suburb vs. a train dependent suburb.

> I would love to see autonomous electric vehicles become our future. I really don't care for public transportation, I find it uncomfortable in many ways

I imagine (edit: many) people who use public transportation would agree with you. You now, since they're usually using it out of necessity and not enjoyment.

For lots of people maybe but no way all. A lot of public transport is faster than driving and it avoids having to park.

Is that true for anything less than a subway/metro train? Light rail is slow, buses even worse, there are many benefits to public transit but speed is rarely one of them. And in the rare cases when it is faster, it's in a handful of extremely dense cities that only represent a fraction of the population, and only for specific use cases.

> I really don't care for public transportation

Right. We get that. It's very obvious that much of the hype around self-driving cars is premised around people who simply reject mass transit outright and therefore believe that somehow, somewhere, they'll get to ride around in a spacious, individual vehicle in the middle of a packed city and so will everyone else and somehow it will all work out because "technology".

> Even if you had a full-autonomous only Interstate where each car could be fully loaded and ride bumper-bumper at over 100kph, it wouldn't even begin reach the carrying capacity of currently existing fully autonomous subways systems like those in Singapore.

This is a poor comparison because cars on highways don't serve at all the same needs as subways in one of the densely populated areas in the world. I'm sure I could construct comparisons where airplanes fail, but a fleet of bicycles succeed(or vice versa), but that doesn't mean that humanity should pick one or the other as the optimal solution.

Autonomous subways are great for places like Singapore, but there are quite a lot of places where throughput is not an issue and where doubling the mass transit subsidies means hiring a second bus driver so the line can run every two hours instead of every four.

Someone mentioned in HN that a bus every four minutes is a very expensive subway train. I think I agree. I think this is the situation for most New York MTA buses at peak hour. These buses should be in a dedicated track on a subway, not sharing lanes with traffic.

> fully autonomous subways systems like those in Singapore

Nitpick, but in Singapore only three subway lines are fully autonomous (CC, DT, NE). The remaining two are not (EW, NS) because they were built with older technologies.

self driving (they dont even need to be self driving just ride share algorithm powered) shuttles are the future of public transport

The systems could be ride share type shuttles that can pick you up at your location and drop you off at your destination.

You make the request in the app and the shuttle picks people up in a location.

They can even drop you off for a transfer with other modes, other shuttles etc. The shuttle that picks you up doesnt have to be the shuttle that drops you off.

Shuttles like these will greatly reduce traffic and can also handle spikes in demand unlike current mass transit.

Singapore? Tokyo? America is different is so many ways I don't even know where to begin.

America had more commuter/passenger rail in the 1940/50s than Europe has today. Russia and China are more spread apart and they both have more high speed real than American has.

Every Australian capitol except Darwin/Hobart and ACT have commuter train systems, and they have the same land mass as the US with 1/6 of the people.

I hate hearing people use the argument you used, because it's just straight up wrong. If American built rail, you'd be surprised to see how quickly development would flock to build around it. American spread out like it did because the nation moved to Interstates.

> Russia and China are more spread apart and they both have more high speed real than American has.

How do you explain car craze in china. Its the biggest car market in the world and one thats growing rapidly. So exactly the opposite of what you are suggesting would happen is happening in china.

China comparisons makes no sense. Car ownership is not accessible to most chinese they have no option but to build a rail system. It is not because ppl prefer travelling in trains(vs cars) its because they have no other option. You have cause and effect reversed. If everyone in china can afford a car like USA they would prefer American interstate system. Who would possibly want to live in cramped quarters built around rail system when you can live in suburban mansion with basement home theatre system.

> Who would possibly want to live in cramped quarters built around rail system when you can live in suburban mansion with basement home theatre system.

Sorry if I sound selfish but it is really scary to think of 1.5 Billion people doing what the 330 million US Americans do.

At some point, I'd argue there is no such thing as sovereignty. I, a neighbor, have a right to not suffocate to death more than you have a right to burn your house to the ground (or I'll take it by force even if I don't have that right).

Is China really more spread apart? It’s a smaller country with a vastly larger population. That population is heavily weighted toward the eastern half of the country, too.

China’s land area is slightly larger than the US

https://en.m.wikipedia.org/wiki/List_of_countries_and_depend...

Huh. Don’t know how I got that mixed up. Thanks.

Edit: Wikipedia’s article on China says, “Covering approximately 9,600,000 square kilometers (3,700,000 sq mi), it is the third- or fourth-largest country by total area, depending on the source consulted.“ Now I’m just confused. Area of a country seems like something there would be broad agreement on.

How do we calculate land area? Is the area more if there's a hill rather than the place being flat? How do we get accurate land areas?

A full train on the Singapore North East Line can carry 1920 passengers (at 6 passengers/m^2), and at rush hour it runs 1 train per 2 or 3 minutes, so it carries 16 passengers/second.

A fully loaded Toyota Corolla carries five people and is 4.65 meters long, so at 100 km/h each lane of the highway would carry 30 passengers/second. So the highway would carry several times more passengers than the subway.

Even though each train can pack more passengers per square meter than a car, it's not possible to run the trains back-to-back at 100 km/h, because they need to stop to let passengers off and on. At rush hour, the rate of the subway system is basically limited by how quickly people can flow from the platform into the train.

You're ignoring space between cars, even with full automation you can't have a highway full of cars with no space between them, else there'd be no room for cars to merge on/off the freeway, and any traffic disruption would cause an immediate traffic back-up. Add one car length of distance and that puts the train in the same ballpark as the freeway lane. (I'll ignore the challenge of filling the Corolla with 5 people - I don't want to be the guy stuck in the middle seat)

Though the problem isn't just throughput of the freeway, but also a question of where all of those cars are going to go when they get to the destination -- generally the commute traffic is going the same place at the same time. Self driving cars may not need a parking space, but if they are going to drop off passengers and then drive away to park somewhere outside of the city center, that causes even more city traffic.

because they need to stop to let passengers off and on. At rush hour, the rate of the subway system is basically limited by how quickly people can flow from the platform into the train.

That's why large train stations have multiple tracks.

A fully-utilized freeway in the way you describe is one that cars cannot easily get on/off of (where is the space for them?). They will have to wait at the on-ramp to be scheduled into a slot. Because of this, the average throughput of a highway necessarily is less than the max-speed max-packed scenario, since the bottleneck is actually the on/off-ramps and feeder streets.

Of course, but the comment I replied to says that the max-speed max-packed scenario has much less throughput than a subway. That's completely wrong, and it's important to point out that it's wrong in order to see where the actual bottlenecks are (at the on/off ramps and feeder streets).

> There's been a lot of tax breaks/money that goes into these programs too, and that's the tragic thing, since that funding should be going to known solutions: public transportation (trains, trams and express buses).

Citation needed.

From the comment guidelines:

> Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something.

Handling 30k passengers per hour is manageable for most rail lines around the world.

Torontos Bloor line does 500,000 daily.

Similarly highways are constrained to their own maximums per lane, and counterintuitively raising the speed limit doesn't help. 1500-1700 vehicles per hour is a fair estimate.

http://buckholztraffic.com/UNF/Data%20Analysis/2%20Lane%20Hi...

He posted unsubstantiated claims about tax breaks (I'd like to learn where there are tax breaks for autonomous vehicles) and a claim about trains having more throughput than an interstate with cars fully loaded moving 100kph bumper to bumper.

Asking for citations might be a shallow dismissal, but stating hypotheses without facts to substantiate them is also shallow.

Did you click on the link? It goes the the article I wrote, which has a ton of sources at the bottom.

That's true, but taking the thread further in the wrong direction only makes it worse.

There are other ways to ask for more information, that open discussion up rather than stiffening into confrontation. Please post in that spirit instead.

A train or subway car can carry at least 10 people per meter vehicle length, while a car is usually some four to five meters long and usually carries only one or two persons. Of course, the comfort factors are decidedly different.

He said an interstate fully loaded. A fully loaded interstate has 10 lanes (5 on each side), and with 10x cars, each 3 meters long with 5 passengers, that's 16.6 people per meter.

Moving 100kph continuously bumper to bumper, not having to stop to let passengers on or off, my bet is that the interstate has more throughput than a subway train.

But how many rails can you fit in the same envelope as an interstate?

None, because trains can't handle the grades that interstate highways generally follow...

I've yet to hear of a subway where there is no space between consecutive trains, however. If there's only one meter of train per hundred meters of track...

That's true, but it doesn't resolve the disagreement. Consider the fact that trains aren't infinitely long, and so they have to slow down everyone to let some passengers off. There's an idea where a train "car" is boarded and accelerated separately then joins the rest of the train while it's moving, but this approach is rarely implemented for many reasons.

> and so they have to slow down everyone to let some passengers off.

So do roads, slow downs happen when cars get on or off of highways.

Going from a road with a high speed to one with a lower speed, if those roads are at capacity, will always result in a backup. Off ramps serve this purpose of course, they basically convert cars going at 60mph into traffic going 30mph through stop lights or some other sort of flow control, but if the roadway is at capacity (as many major cities are), that off ramp as a flow control mechanism falls apart and cars pile up onto the freeway.

The math is unfortunately independent of self-driving cars. If every car is self driving capacity does increase, cars can self coordinate and some of those stop lights become unnecessary, but if 100 cars want to get onto a road that has room for 20, someone is going to have to wait!

Subways naturally don't have this problem!

This argument seems to compare 1 interstate hwy to 1 rail. In fairness to the autonomous vehicles, there's many road routes to most places. Road infrastructure costs a tiny fraction of rail infrastructure.

Roads also allow for multiple lanes. This allows for somewhat degraded service when something goes wrong; a train stopped on the tracks blocks everything. With multiple lanes, roads can be maintained while still in service. Every subway struggles with maintenance windows.

I'm not saying one is always superior to the other - trains have their niche, but it's a niche that will never be as broad that of autonomous cars.

> Road infrastructure costs a tiny fraction of rail infrastructure.

Not necessarily.

Rail is cheaper to maintain, and there is a huge opportunity cost of paving over a cities most valuable real estate to make roads.

The math on how large the streets would need to be in downtown Seattle to alleviate traffic end up with a giant % of downtown Seattle being torn down and paved over.

The Urbanist has a good article (https://www.theurbanist.org/2016/10/12/brt-is-not-cheaper-th...) on why light rail is cheaper than a huge freeway.

Rail can also have multiple tracks, it costs more, but amortizes really well.

Not having to intermix pedestrian, bicycle, and cars is another huge win for, well constructed, rail projects. Autonomous cars still have to stop at crosswalks! In urban cores, stop lights seriously cut into average MPH for a trip, and start shifting things into favor of rail.

We definitely need at least four train tracks for mass transit to work. Two tracks each way: one express and one local.

What I don't understand is why do autonomous self driving cars and subways have to be either or. Why can't we do both? After all, we can't use the subway for ambulances and fire trucks so we still need to build some kind of roads even if we had full confidence in the subways...

Just thinking out loud... Unless we had helicopters for emergencies?

Can we have a town with no paved road? Only sidewalks? That's still paved, right? Can trash collection also take the subway?

With true self driving technology it's plausible the cars on the road will be notably different than what we have today, which might significantly increase the roadway carrying capacity.

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