We can drastically reduce our usage of jets though. There is no reason why people should be flying between SF and LA, or NYC and Boston. Those are well within comfortable range of high speed rail, which is electric.

Once we’ve shifted all the excess air travel over to rail, that will leave a much smaller set of jet travel to offset.

If you look at a map of all airline flights there are many thousands of short-range flights. Replacing them all with trains would be interesting. Just the right-of-way property transactions would be daunting. Look at California as a lesson in how this can't be easily done.

The other thing is, people move around. Airlines can change flights easily to map to demographic changes; that's a major strength of air travel. Not as easy to rip up tracks and start over.

It's much easier, IMHO, to switch over these short haul flights to electric aircraft than to High Speed Rail in the US. By the time even one major new HSR route will be finished, we'll have certified and be flying electric passenger aircraft with just as much speed and just as long of a route (500 miles) BUT with ability to go anywhere in the country by hopping.

I kinda doubt it will go that quickly. See how many problems Boeing had with their lithium batteries in the 787. And those were just auxiliary power. This will take a hundred times that many batteries with the scale bringing many engineering challenges. And then the totally different engines.. I think it'll take a long time to have a battery powered airliner built, in mass production and as reliable and safe as current airliners. There's a lot of stuff to be built from scratch without half a century of trial and error to learn from.

I think biofuels might be a better option for aviation until the tech has time to catch up.

I'd love for that to be true, but I am quite dubious. Flight technology tends to be very weight sensitive, and our battery densities are just nowhere close to the density that flight needs.

Current batteries have an energy density of 90-190 Wh/kg, depending on the specific chemistry. Jet fuel on the other hand has an energy density around 12,000 Wh/kg. Obviously some amount of that will be made back up with the relative light weight and high efficiency of electric motors, but that is a very step energy difference to overcome.

A quick bit of Googling says that turbofan engines are about 40% efficient, while triple phase electric motors are roughly 85% efficient. Given the 3,000 nautical mile range of a 737NG, some back of the envelope math says that an EV equivalent would have a range of about 100 miles at best[0]. Forget LAX -> SFO, this isn't even enough to get you from LA to Bakersfield. And even 100 is optimistic, given that the FAA requires that all planes have extra fuel for diversions, weather, holding, etc.

At this point, I suspect it might be easier to refine kerosene out of capture CO2 using excess renewable energy than it would be to make an EV 737 replacement.

0 - I'm obviously not accounting for weight and aerodynamic differences, which are beyond my capability to estimate, but I doubt that would make a significant difference. I'm also assuming that we're using Li-Ion Cobalt batteries, which have the highest density. The more common Phosphate chemistry makes these numbers even more bleak.

The best lithium ion batteries have 300-400Wh/kg (some cells do up to 650Wh/kg with sulfur), electric motors can have up to 95% efficiency. Long range jets can fly 20,000 km with passengers. Easily enough to do 500 miles. But if you improve aerodynamics, can go much further.

Source on 400-650Wh/kg? That’s significantly higher than what’s even reported in Tesla EVs, and I’m curious if that’s lab or production figures. Even going up to 400Wh/kg and 95% efficiency only yields 237 miles for a 737 equivalent, which isn’t enough.

The top spec 777 would give you 677 miles on batteries, assuming 400Wh/kg. Enough to serve the LAX to SFO route, but a fairly limited vehicle all things considered, especially for the price and size.

> Long range jets can fly 20,000 km with passengers.

Sure, but economics begins to dominate here. There’s a reason I chose the 737 as a reference benchmark; it’s the gold standard of short to medium range airliner, and absolutely the vehicle that we should be aiming to minimize. If you have to pull out a 777 sized aircraft to service LAX -> SFO, then the price of tickets is going to begin rising significantly to cover the higher vehicle cost. I’m also genuinely quite doubtful that many airports can handle 100% of their jets switching over to wide body aircraft, which this would require, without significant improvements to the terminals and other facilities. If governments are forced to upgrade airports to save money on rail, I’d argue that that’s penny wise and pound foolish.

All of this can be done, of course, but it really begins to erode all of the supposed cost savings over HSR.

> If you look at a map of all airline flights there are many thousands of short-range flights. Replacing them all with trains would be interesting.

Replacing “them all” is to set the bar unnecessarily high. I suspect there’s an 80/20 rule in effect here, and we should aim to replace the most popular short haul routes, not all of them. That’s why I specifically called out SF->LA. Major population centers within a few hundred miles of each other are prime HSR targets, and in countries with HSR we see a lot of passengers preferring rail for these exact types of trips.

There’s no reasonable world where every single small town gets a high speed rail running to it, but we shouldn’t set that as our goal. Don’t let the perfect be the enemy of the good. In particular there are nice stretches of good density along the coasts of the US that seem like prime targets for high speed rail, that would make travel more ecologically sound and comfortable for a large chunk of the population.

> Just the right-of-way property transactions would be daunting. Look at California as a lesson in how this can't be easily done.

And yet right of way transactions regularly pass for highway and highway expansions. Not without difficulty, but they get done. Letting rail projects grind to a halt while forcing road ones through is a political choice, not a law of nature.

> The other thing is, people move around. Airlines can change flights easily to map to demographic changes; that's a major strength of air travel. Not as easy to rip up tracks and start over.

This is only kind of true. Changing routes is easy only to a point. Expanding and refitting airports to handle increased traffic can be incredibly expensive and slow. LA is going to spend a huge amount of time and money trying to fix not just their airport, but also the transit to their airport which is currently overwhelmed.

My city is probably well on its way to its airport being incapable of handling the recent population growth. Expanding that airport and improving transit to it will be massively expensive, and require the eminent domain of a lot of property.

Secondly, while people do move around, it’s not like they’re throwing darts at the map and moving there. The places Americans are moving to are easily predictable; they’re moving to cities. You’re not going to wake up one day to discover that America has moved to the middle of nowhere Kansas.

Generally the cities that would make the best HSR targets are also the least likely to totally collapse in population too. NYC isn’t going anywhere, neither is Boston or Philadelphia. One would be forgiven not predicting the rise of say, Denver, but that doesn’t mean we shouldn’t at least be aiming for HSR to the obvious targets.

And thirdly, transit availability and where people move is a two way process. People like and care about access to transit options, and the quality of the local airport (and cost of flights) is already one thing that people consider when they move to a new location. There’s no reason to believe that access to HSR wouldn’t be the same. Especially since it’s possible to put HSR stations in far more convenient locations, given the lack of turbine noise to piss off the neighbors.