JR Joban Line E531 Series Train Leaving Shinagawa Station 3

There is a button beside each door. If the door button system is active, passengers have to push the button to open the door. Its purpose is to prevent air exchange so that the temperature inside the train would not change. I have not seen the system is active in core area of the city. Maybe it is meaningless in busy sections because all doors will be opened anyway.

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