The problem with our subway system is that the doors open on alternating sides

When I went to Singapore,
at least 5-6 stations in a row opened on the left side,
and then the next 5-6 stations opened on the right side.
It was designed that way, so the passenger flow was incredibly efficient.
But in Korea,
the sides keep switching back and forth between left and right,
causing people to get pushed around inside the train.