Lines in front of car doors to keep a smooth flow (and order) or oncoming/offgoing passengers.
Stay to the right? Lines on the floor that align with car doors. Lines will be on passengers' right so that departing passengers can more smoothly exit on their right (like car traffic, but with people!) It will keep passengers from running in to each other at the door and will reduce people forcing themselves on to maxed out trains (excuse me, but you need to get in line. I was here first).