[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)