[XCabbage]

I would guess that what matters most is stops for driving disqualified/uninsured/unregistered, DUI, running lights, and failing to yield (especially at crosswalks), and perhaps for speeding on non-highway roads where it has more of a safety impact. As you say, in the USA as in virtually every culture, almost everyone speeds in some contexts, and especially on big, multilane, motor-vehicle-only roads; enforcement of speed limits in that context is likely one of the lowest impact things police can do, but I think it's a massive error to treat "traffic stops" as a category as equivalent to that sort of enforcement specifically.