Hacker News Reader

> An airport runway can handle far more people than a rail line.

Definitely false. The most efficient runways (say Gatwick) manage 8-9,000 pax per hour, with a huge chunk of departures delayed due to runway congestion. The Tokaido Shinkansen line manages more than 20,000 per hour and most are on-time (and could run at night because noise is less of an issue).

It helps that 750-pax trains take a minute to board and can be run every 3-4 minutes if needed.

Not bullet trains. As speeds increase, the safe distance between trains (both in time and space) must also increase. No rail line (line, not station) can handle one bullet train every minute. A large railway station can indeed handle more than a single runway, but apples and oranges. A rail station can have multiple rail lines just as an airport can run multiple runways.

Maybe not every minute, but in Japan, the same track can handle a new bullet train every few minutes, like clockwork. The throughput is enormous. And the footprint of a track is much, much smaller than a single runway, so it's not uncommon for even modest rail stations to have 15+ tracks. Chicago O'Hare has the most runways of any airport in the US, at 8, and they aren't all usable at the same time, since they intersect, and wind direction varies. And that's an enormous facility.

But in the same area for 1 runway + required buffer, you can fit A LOT of train platforms (also including required buffer, which is essentially nil).

I was thinking BART ten car trains carry as many passengers as two 747's or five 737's.

high-speed trains generally have lower capacity (and better seating), usually 300~600 though they're normally designed to be coupled (you can pair two trainsets) into a "single train", passengers can't move from one to the other but the sets are solidly linked and behave as a single train for density purposes).

The N700 shinkansen is the big exception with >1300 seats 16-cars trainsets, though it's on the slow side (tops out at 285km/h). The CR400 comes close with 1200 seats 16-cars trainsets (and an operational speed of 350, which should eventually be increased to the design speed of 400).

> Airports can land a plane every minute. A rail line would never dare have two high speed trains that close to each other.

Why the difference? If I naively guessed, I would think that trains were easier to control and more predictable, so the docking rate should theoretically be higher than for a plane.

Is the real limitation not the docking, but the high speed travel up to he docking? Trains all follow the same track, but planes can travel in parallel until 5e final approach?

Because if a plane has a problem, those behind it can maneuver around in three dimensions. Trains move in one dimension. If a train has an accident (ie comes to an unexpected stop) the trains behind it must be far enough away that they can also stop. They cannot maneuver around the blockage. Allowing for detection and communication times, at 400+kph that safety margin will be much more than a minute.

That’s technically true, but for any distance that is resembling of a train’s stopping distance, planes are fairly one dimensional, too. Passenger planes feel agile from the inside, but from the outside they’re just about a hundred tonnes on a tube of aluminium hurtling forwards at all costs, with just about as much steering capability as that begets.

The limitation for train capacity is the need to maintain a "block" to ensure that a train has enough time to brake in the case of an emergency, without hitting the train in front of it. For Japan's high speed rail, it takes ~2.5 miles to stop a train.

On top of that, many railroads still operate with a static set of blocks, where the track is divided into areas called blocks that do not change over time. Only one train has essentially a lock on a block at a time. So a train has to own the block it is on, but also needs to get access to the next block early enough to avoid an emergency braking event. This reduces the capacity of a line.

There's a movement towards "moving block" systems, where railroads use sensors to track train movement and create a moving buffer around the train, which should increase capacity.

> A rail line would never dare have two high speed trains that close to each other.

Maybe not every minute, but the bullet train runs every 10 minutes during peak hour with up to 1300 passengers. I don't think that capacity is adequate for measuring 'faster' here.

1300 every 10 minutes = 130 people per minute. A normal 2-lane road can achieve better using buses.

You only get at most about 1500 cars per hour per lane. Or 25 cars per minute.

That's why I said buses. This issue has been studied many many times. The dirty secret is that dedicated 'bus only' lanes, with lots of full buses using them, move more people across a point per minute than most any other ground option.

100 people per (large) bus at 10 busses per minute = 1000 persons per minute. That rivals a runway full of a380s for shear people-moving power.

How long does it take to get 100 people in a bus?

China is building driverless low-medium speed maglevs:

https://www.cnn.com/travel/article/china-driverless-maglev-t...

I’d like to see one of your studies to see the assumptions.

60 mph buses don’t really seem like a great way to travel.

China carried 10 billion people by high-speed rail last year.

http://www.globaltimes.cn/content/1149608.shtml

> Airports can land a plane every minute.

During peak times this is true, but the ramp is still a huge bottleneck for overall capacity at most airports. Listen to the ground control frequency at a busy airport like JFK for a good example of this.

I guarantee you CN has lines connecting Calgary and Vancouver today.

Not for passengers. Not anything that in any way competes with flying.