遽 is literary, meaning 'suddenly, hastily'. Common in 遽然 ('abruptly') and 不遽 ('not in a hurry'). Its ancient noun sense, a relay post-horse for fast couriers, is the origin of the 'speed' idea.
memory
The walk radical 辶 plus a charging beast: think of a courier galloping a relay horse along the road at top speed, that is 'suddenly, in haste'.
The walk radical 辶 is written last in stroke order. It brings the idea of travel and motion, fitting the original meaning, a fast relay horse speeding along the road.
