The four-day weekend has a geography problem. Everyone who has been meaning to see the Pacific tries to see it at once. The TRA east-coast trains on Thursday evening are standing room with children, coolers, and the particular silence of people who know they have made a mistake.
If you already have a reserved seat, go. If you do not, do not “see how it looks at the station.” It will look like a station on the night before a holiday. Yilan, Jiaoxi, Hualien, and anything past Ruifang will still be there on the weekend of October 3, which is an ordinary Saturday.
The HSR west coast is the other version of this error: Tainan and Kaohsiung are possible if you book a reserved car today. Non-reserved on Thursday is how you stand from Banqiao to Taichung with a pomelo bag. Friday morning trains are kinder than Thursday night, and still fill.
This Sunday is still a window for a short trip that does not require a reservation — Beitou, Tamsui, a silvergrass hour on Yangmingshan if the buses have not already become a queue. The east coast is a weekend you plan. It is not a weekend you improvise on the 24th.