Originally Posted by
JerryFF
It's a lot cheaper and safer to build doors that open in response to pressing a button than to sense when the train has stopped at a station and it is safe to open the doors.
The train doesn't have to 'sense' when to open the doors any more than it senses when to activate the open/close button. It is the conductor who activates the buttons, who could instead open ALL the doors.
I've seen subway trains and city trams capable of doing both - the conductor/driver can either open all the doors or activate the buttons and let the pax open them.
So I don't think it's the cost (at least not the one that you mentioned).