>> a much more sustainable form of transportation compared to aviation.
Night trains are not like normal trains. They carry far fewer passengers per car. That doesn't make them as bad as flying on pure CO2 emissions, but night trains are not as efficient as "trains" generally. They are more comparable to luxury busses. But ... if the other option is an electric car, or even an electric aircraft, then even an electric night trains will likely no longer win on CO2 emissions.
Seating rail cars have 70-90 seats, whereas couchettes have 40-66 beds, but at lower emissions (lower speed->less drag) and higher occupancy (in Germany, occupancy is around 50% for day trains). It’s pretty much a wash. If you mean luxury sleepers, they’re worse sure. None of the startups are really targeting those luxury/low density levels, because of the overall poor impact.
Flying has around 10x the co2eq emissions of trains (300g/km, including infrastructure, occupancy). Cars are still pretty bad, but also don’t compete well for 1000km trips in Europe. It’s basically only aviation at those distances.
Electric airplanes that can do 1000km trips don’t exist. They may exist one day in significant quantities… but perhaps only after we’ve used up all our carbon budget on the path to a 2-3C increase.
> night trains will likely no longer win on CO2 emissions.
The comparison is more complicated though isn’t it? It isn’t a comparison with a plane, it’s a variable comparison with a plane, a taxi, and a hotel etc.
Night trains are not like normal trains. They carry far fewer passengers per car. That doesn't make them as bad as flying on pure CO2 emissions, but night trains are not as efficient as "trains" generally. They are more comparable to luxury busses. But ... if the other option is an electric car, or even an electric aircraft, then even an electric night trains will likely no longer win on CO2 emissions.