Mark Brader:
The upper deck would have to have doors that open about 8-10 feet
(2.5-3 m) above rail level. Which means that if those doors ever
opened outside a station, someone could fall out and break their neck.
I find it hard to believe that safety authorities anywhere would
accept that.

Neil Williams:
Someone could fall out of a normal train's doors and break their neck...
Someone could also fall off a station platform as-is, but this seems
not to happen with any frequency.

Actually it does. But safety authorities tend to be more worried about
*new* hazards.
--
Mark Brader "Finally no number of additional epicycles can
Toronto hide the fact that We've Got a Problem Here."
-- from a science book club promotion

My text in this article is in the public domain.