The timing lines up but that's more of a vibes argument.
The majority of traffic stops in the US are, cop parks on the side of the highway somewhere the speed limit is lower than the speed people drive there, every car on the highway is doing 70 in a 55, whoever drives past gets a ticket and the government fills their coffers but the speed everybody actually drives on that stretch of highway remains 70.
Now suppose the cops stop doing that for the stated reason. If you then drive past them at 110 instead of 70, are they still going to not pull you over? Good luck with that. Even if they're actually trying to minimize traffic stops, that one's the one that makes the cut.
So then what happens if they stop doing the usual ones? People are then going to drive 70 in a 55 because they can get away with it, but that's what they were doing to begin with. You could argue that the fatality rate would be higher at 70 than 55, but then why would that change relative to the baseline where that was what was already happening?
So the argument would have to be that idiots had the impression that they could do 110 without getting pulled over, even if that wasn't true, and then did that and managed to make contact with an overpass before driving past a cop. Which doesn't seem as plausible, because speeds like that on empty desert highways shouldn't have raised the fatality rate that much (e.g. it's not that high on the autobahn in Germany), and speeds like that in traffic where there are other cars traveling significantly slower will trigger a visceral feeling of danger in nearly all humans unless they're on drugs or have significant mental health issues, and in those cases they wouldn't have been deterred by the prospect of traffic enforcement anyway. Which is why people drive somewhat over the speed limit even when that could get them a ticket -- because it doesn't feel dangerous -- but also why they don't drive a lot faster than the other cars -- because that does. Traffic enforcement or not.
Moreover, regardless of how much of a contribution was made by that vs. COVID, the numbers still don't line up with it being vehicle safety regulations.
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.
The majority of traffic stops in the US are, cop parks on the side of the highway somewhere the speed limit is lower than the speed people drive there, every car on the highway is doing 70 in a 55, whoever drives past gets a ticket and the government fills their coffers but the speed everybody actually drives on that stretch of highway remains 70.
Now suppose the cops stop doing that for the stated reason. If you then drive past them at 110 instead of 70, are they still going to not pull you over? Good luck with that. Even if they're actually trying to minimize traffic stops, that one's the one that makes the cut.
So then what happens if they stop doing the usual ones? People are then going to drive 70 in a 55 because they can get away with it, but that's what they were doing to begin with. You could argue that the fatality rate would be higher at 70 than 55, but then why would that change relative to the baseline where that was what was already happening?
So the argument would have to be that idiots had the impression that they could do 110 without getting pulled over, even if that wasn't true, and then did that and managed to make contact with an overpass before driving past a cop. Which doesn't seem as plausible, because speeds like that on empty desert highways shouldn't have raised the fatality rate that much (e.g. it's not that high on the autobahn in Germany), and speeds like that in traffic where there are other cars traveling significantly slower will trigger a visceral feeling of danger in nearly all humans unless they're on drugs or have significant mental health issues, and in those cases they wouldn't have been deterred by the prospect of traffic enforcement anyway. Which is why people drive somewhat over the speed limit even when that could get them a ticket -- because it doesn't feel dangerous -- but also why they don't drive a lot faster than the other cars -- because that does. Traffic enforcement or not.
Moreover, regardless of how much of a contribution was made by that vs. COVID, the numbers still don't line up with it being vehicle safety regulations.