Thank you. I didn't know about that requirement; and it would obviously be ridiculous to stipulate that airframes be made heavy.
This is one reason why U.S. trains have (relatively) 'harsher' requirements than other countries where track is not shared to such a high extent.
Separately, this degree of track-sharing is one of the reasons why average passenger rail journey speed has decreased in many places over a 100-year time period!
Obviously, in both cases, there are many many factors involved - but, an important element.
Ever notice how every wheelie cart on a plane has not one but two locking handles to secure it? How about the ram air turbine [1] which is used almost never but weighs hundreds of pounds? Seat frames are still made mostly of metal, whereas if weight were the only consideration they would probably be carbon fiber.