Why is nobody talking on the train?

Short answer

Phone calls are what is being avoided, not conversation. Keep the phone on silent, and on a long-distance train take the call between cars.

Passengers riding a Tokyo Metro train at rush hour

What the rule actually is

The tourism board's guidance is narrower than the silence suggests: carry your phone on silent mode, and avoid speaking on it. Speaking at any volume on a phone is the thing frowned upon while riding trains and buses — not talking to the person beside you.

So the quiet is partly a by-product. Conversation does happen, at a lower volume than you may be used to, and the phone rule removes the one sound that would otherwise carry down the whole carriage.

Where you can take a call

On a long-distance train such as the shinkansen there is a designated answer: the vestibule between cars. Step out, take the call there, come back to your seat.

A commuter train has no equivalent space, so the practical move is to let it ring and reply by message. Nobody expects you to answer, and stepping off at the next station to talk is normal rather than odd.

The rest of the unwritten set

Queue to the side of the doors and let passengers off before you board. Priority seats go to elderly, pregnant and disabled passengers, and are treated as genuinely reserved rather than merely suggested.

"If in doubt, follow the locals" is the tourism board's own fallback, and on a train it works better than it does almost anywhere else, because the behaviour is uniform enough to copy in a few seconds.