"Please hold the handrail during the whole journey" in Chinese/Cantonese? (As heard in Hong Kong airport trains)
In the video the Mandarin is:

請沿途緊握扶手


This Google webcache also says:

九巴的勸喻，貼在車廂扶手左右：「 上 車 後 請 沿 途 緊 握 扶 手 」，英 語「 Please hold the handrail during the whole journey. 」為 九 巴 的 愛 心 ，我 不 能 不 長 嘆，釋放善意。

It seems like a common saying on public transportation in HK.