Ｕシートとは、要はグリーン車両の指定席ですね。
1時間あとの列車だと席が残ってたので、1時間待ってでもそれに乗ればよかったです。
もう二度と普通車両に乗らない！(^^;)

結局新千歳の一つ手前の駅で、本当に乗客乗れませんでした。

U-seats are, in brief, reserved seats on 1st class cars. There were still seats remaining on the train that was coming an hour later, so we should've taken that one, even if it meant waiting an hour. I'm never riding in a second-class train car again! (^^;)

In the end, at the last station before New Chitose, passengers really couldn't get on board.