the flow of traffic is inherently unpredictable

Finally! An authority -- or, at least, somebody -- who echoes what I've been saying for years:

. . . the flow of traffic is inherently unpredictable. As a result, we don't habituate to the suffering of rush hour. (Ironically, if traffic was always bad, and not just usually bad, it would be easier to deal with. So the commutes that really kill us are those rare days when the highways are clear.) As the Harvard psychologist Daniel Gilbert notes, "Driving in traffic is a different kind of hell every day." [Emphasis added.]

Andrew Sullivan