This is an interesting read on that subject: https://www.lowtechmagazine.com/2013/12/high-speed-trains-ar... One of the many complexities involved is the fact that high-speed trains on existing lines take up much more track space and push out slower-moving trains which link up the smaller stations. So city-to-city is fine, but towns and below get a reduced service, leading to more car traffic to get to stations (and more pure car journeys).

This makes the point that the more trains are powered by clean electricity though, the better: https://www.lowtechmagazine.com/2007/04/planes-on-whe-1.html

I remember some paper looking at this question, and if you took into account the train infrastructure, planes were not too far off. But train has other advantages such as reduced noise pollution, being able to bring you right to your destination, and not being hijackable into buildings.

The big advantage is that you can easily run trains off of CO2-neutral electricity. The answer to my question heavily depends on how the electricity mix looks like.

> The answer to my question heavily depends on how the electricity mix looks like.

Yes, but the electricity mix will continue to move towards more renewables. Air travel will continue to use fossil fuels.

Indeed, there is pretty much 0 feasible way of moving air travel to carbon neutral energy. Even biofuels are simply not economically feasible and may well never be, and batteries are a no-go.

The train infrastructure over 50 years? I doubt if air travel is even close to as environmentally friendly

The real problem with not doing the trains is the right of ways become difficult.

California wanted to build high-speed rail in the 1970s but the car culture won. They kept expanding the highways.

Now they can’t build directly between SF and LA, for example.

People also overlook that trains can make a few stops along the way.

China transports over a billion passengers a year by rail. Put them in the air

Also by building dedicated express and high speed train lines (such as we're doing in the UK with HS2) you enable the stopping services to be far more efficient and frequent, which means more people can use them.

> Now they can’t build directly between SF and LA, for example.

Geography and geology make building HSR between LA and SF difficult. You'd need to bore through a bunch of mountains to get to the Central Valley and then bore through more mountains to get to the SFBA.

i imagine building the more direct route in the 1970s would have been much cheaper, even after adjusting for inflation

The Coast and Traverse Ranges in California have been around a little longer than the 1970s.

Are planes really more noise pollution? I agree they create more concentrated noise, but they seem to be less noisy overall than trains since planes are quiet once in the air.

I rented a warehouse in Millbrae near the SFO international airport for a year. The noise pollution is obnoxious, but the air pollution is way more of an issue.

Commercial jets starting, idling, and taxiing are incredibly dirty machines - it's nowhere near their optimal operating conditions and it's not like they have catalytic converters cleaning up their exhaust.

Furthermore, even though they're not supposed to jettison fuel before landing anymore, I'd find what were clearly oily droplet stains on my convertible's rag-top disturbingly often. Busy international airports are environmental disasters.

HSR seems like a complete no-brainer for domestic travel from where I'm sitting, if only we could get the lines built in the US.

Yes. The noise impact of trains is measured in hundreds of feet (maybe thousands if a locomotive is blowing a horn at a grade crossing). The noise impact from an airport is measured in miles.

Furthermore, for a given noise level, any number of surveys have shown that noise from planes is more annoying than from trains or roadways.

I've lived ~250m from train tracks and ~10km from an airport, the latter was way more annoying.

Honestly the most annoying part of living next to the train was waiting for the level crossing.

Depends; if you use renewable energy, operating it could pretty much be neutral. Given that this is in China, I would expect them to mostly power this with renewables (wind, hydro, or nuclear). They do still build a lot of coal as well of course.

Steel production for the infrastructure could long term also be a lot cleaner but is short term likely to have a substantial CO2 footprint. But that would be similar to other high speed rail options. Probably, over the life time of the installation, it would be quite good.

How do you amortize CO2?

You take out a loan from the CO2 bank with CO2 bring charged as interest, and then slowly pay it back over the course of a few decades. How much you pay back is something the atom counters figure out, I'm naught but a humble Oxygen farmer.

You guesstimate how much CO2 was released during construction, and divide by the expected lifetime of the structure and add a guesstimate for the CO2 used for maintenance.

CO2/(passenger*km), not CO2.

Also, how do you amortize the alternatives? e.g. the airports, getting to the airports (which are further from city centers than train stations), etc?

Don't forget that airplanes spend their time at altitude where this is much less wind resistance.