Generally speaking, it's quicker to travel by train.

generally 是形容词 general 的副词形式，意思是"通常地、普遍地"。 speaking 是动词 speak 的现在分词形式，意思是"说、讲"。 generally speaking 是一个固定搭配，意思是"一般来说、通常来说"，用于表达普遍情况或观点。