I'm so used to the noise of traffic in Seoul that I hardly notice it anymore, and it certainly doesn't interfere with sleep. Aren't humans wonderfully adaptable creatures? When I was in college there were train tracks that ran right in front of our campus and by my dormitory, and the train noises ceased to bother me after the first week or so, no matter what time they ran by.
This morning, my first at "home" in America in over a year, my sleep was broken by the complete lack of traffic noise. We have birds, we have coyotes, and . . . oh, wait! That's a tractor I hear now! Thank God for motorized vehicles.