This is the 787th most frequent Chinese word.
快速
"快速" means "fast" or "rapid."
In this sentence, '快速' is used as an adjective modifying '动作' (action), indicating the high speed of the movements.
他以快速的动作完成了工作。
He completed the work with rapid movements.
Here, '快速' functions as an adverb describing the manner in which the train passed, emphasizing swiftness.
火车快速驶过桥梁。
The train rapidly passed the bridge.
In this case, '快速' describes '方法' (method), adding a context of efficiency and speed in its implementation.