I once bought an overnight train ticket from France to Italy, instead of spending more on a high-speed train ticket and a hotel night. It would have been a gre

I once bought an overnight train ticket from France to Italy, instead of spending more on a high-speed train ticket and a hotel night. It would have been a great idea, if the train didn't have its heater stuck on, in August, and a broken emergency pull cord in an unknown car, which resulted in multiple unintended stops that required the staff enter every cabin to reset the pull cords, before resuming. I learned to check the reputation of the train line, like I would a hotel. Anyway, traveling efficiency is a factor of the speed and size of the vessel and the viscosity of what it's traveling through. It's non-linear, and scaling up the vessel size slowly adds efficiency, and speeding up the vehicle or increasing the viscosity quickly reduces efficiency. Boats have an advantage by getting very big, but a really, really big disadvantage if they go fast, which is why huge boats going slow is their most common use, mostly for cargo, but sometimes for people, when the ship itself can be a destination. Trains can't get very big, but air is much less viscous than water, so they can go a few times faster without major losses. This is why rail is really popular for transporting cargo across the US and Canada, although it's not fast enough for long distance passenger travel. The absolute peak in energy efficiency comes from a large vessel moving through a very-low viscosity atmosphere, which is what airliners are able to do, by traveling in the stratosphere, eliminating the majority of the drag, and allowing for effectively uncapped speeds. Really, the faster an airplane can travel, the higher it can go, further reducing drag and increasing efficiency. The limit is technological, not physical, but current airplanes traveling around mach 0.8 get very high cruise efficiency from both being large and being in a low-viscosity atmosphere.