[jltsiren]

> Very light trains. Think lighter than road cars, since they don't need crumple zones or crash worthiness.

Crashes involving light rail are common in urban areas, because the trains share streets with cars. I don't see that going away as long as human-driven cars are allowed. And because passengers are often standing, the trains must be heavy to improve passenger safety in crash situations.

> Virtual coupling. Basically platooning on rails.

Modern designs typically have very long cars, with only 1, 2, or rarely 3 cars in a train. Longer cars increase passenger capacity and improve space utilization, because passengers can move around freely. They also allow busy passengers save some time by exiting from the right end of the train.

> Much faster acceleration and deceleration. With leaning, they could also corner faster.

Urban trains already limit acceleration and deceleration to improve passenger safety and comfort. Long-distance trains with sitting passengers and grade separation are another matter.

[avidiax]

> Crashes involving light rail are common in urban areas,

That's a good point. That doesn't mean that trains need to be as heavy as they are, though. Having a crumple zone and weighing 3x of non-commercial road vehicles would still be quite a bit lighter, and would provide safety.

> Modern designs typically have very long cars

I live in Switzerland, and it's common to have train combinations that are very long here, even with long cars.

> limit acceleration and deceleration

There are limits, of course, but they can be relatively high if you strictly control "jerk". That's where computer control comes into play, as it requires high driver skill to stop the train at the right position while limiting jerk.

https://en.wikipedia.org/wiki/Jerk_(physics)