I take the metro almost every day and have been for years.
I still remember the days when people rushed into the metro as the doors opened, making it difficult for people to first exit the metro. People waited for the metro, right in front of the place where the doors would open, making it very hard to exit.
I realize the arrow stickers on the metro floor are nothing new, but I want to highlight their simple yet effective design. Now, instead of standing directly in front of the doors, people stand off to either side, and wait for those who are exiting to exit the metro before entering. While there are still the odd few who ignore the arrows and barge right into the metro, most people, miraculously, have (perhaps subconsciously) started to follow the directives on the floor and now wait for their co-transit-riders to leave the metro before jumping in themselves. A simple, effective design solution to a vexing problem.