I think it equally affects quality of life during non-sleep hours though as well. The incessant horn honking, blaring music and the straight pipe folks actually make walking down the street unpleasant. The sad thing with the horn honking is that the people in the others cars that they're honking at have their windows up, air conditioning and stereo on. They likely can't hear it enough to be bothered by it. The people that pay price are the walking pedestrians i.e they very people who are not contributing to the very traffic problem these people are stressed about. What's the point in a walking city when the walking has been ruined by people in cars.