they’re recognizing the limits of precise measurement
I don’t think this explains such a big discrepancy between the nominal speed limits and the speeds people actually drive at. And I don’t think that discrepancy is inevitable; to me it seems like a quirk of the USA (and presumably some other countries, but not all). Where I live, we get 2km/h, 3km/h, or 3% leeway depending on the type of camera and the speed limit. Speeding still happens, of course, but our equilibrium is very different from the one described here; basically we take the speed limits literally, and know that we’re risking a fine and demerit points on our licence if we choose to ignore them.
Yeah. Other folks have already mentioned that the degree of enforcement leeway in the U.S. increased when the federal government made artifically-lower speed limits a requirement of federal highway funding in the 1970s. Which I can’t confirm or refute, but does make sense: I imagine that some states who disagreed with the change might have grudgingly set the formal limits in line with the federal policy, and then simply used lax enforcement to allow the speeds that they preferred all along. I have noticed that it’s often seemed politically unpalatable for officials to stick to a program of stricter enforcement to rein in a particular area’s entrenched driving culture after speed limits were increased in the 1990s, though.
In any case, if folks think that part of the reason for lax enforcement is measurement error then that could be used as an input toward designing a separate maximum speed designation. One could keep the “speed limit” enforceably defined in terms of the actual vehicle speed, while defining a new parallel “maximum speed” constraint strictly in terms of a measurement taken by law enforcement equipment that passes a particular calibration standard within a particular window of time before and after issuing the citation. Then you’d end up with one standard that gives the benefit of doubt on measurement error to the driver and another that gives the benefit of doubt to the enforcement record, and thus there’s a logical reason for (at least some of) the spread between those two thresholds. (This legal system might also make it easier to move toward maximum-speed enforcement that works more like existing license-plate-based tolling systems, allowing for a much more pervasive enforcement regime to push the culture toward compliance without the downsides of setting up lots of direct conflicts between irate drivers and law enforcement officers.)
I don’t think this explains such a big discrepancy between the nominal speed limits and the speeds people actually drive at. And I don’t think that discrepancy is inevitable; to me it seems like a quirk of the USA (and presumably some other countries, but not all). Where I live, we get 2km/h, 3km/h, or 3% leeway depending on the type of camera and the speed limit. Speeding still happens, of course, but our equilibrium is very different from the one described here; basically we take the speed limits literally, and know that we’re risking a fine and demerit points on our licence if we choose to ignore them.
Yeah. Other folks have already mentioned that the degree of enforcement leeway in the U.S. increased when the federal government made artifically-lower speed limits a requirement of federal highway funding in the 1970s. Which I can’t confirm or refute, but does make sense: I imagine that some states who disagreed with the change might have grudgingly set the formal limits in line with the federal policy, and then simply used lax enforcement to allow the speeds that they preferred all along. I have noticed that it’s often seemed politically unpalatable for officials to stick to a program of stricter enforcement to rein in a particular area’s entrenched driving culture after speed limits were increased in the 1990s, though.
In any case, if folks think that part of the reason for lax enforcement is measurement error then that could be used as an input toward designing a separate maximum speed designation. One could keep the “speed limit” enforceably defined in terms of the actual vehicle speed, while defining a new parallel “maximum speed” constraint strictly in terms of a measurement taken by law enforcement equipment that passes a particular calibration standard within a particular window of time before and after issuing the citation. Then you’d end up with one standard that gives the benefit of doubt on measurement error to the driver and another that gives the benefit of doubt to the enforcement record, and thus there’s a logical reason for (at least some of) the spread between those two thresholds. (This legal system might also make it easier to move toward maximum-speed enforcement that works more like existing license-plate-based tolling systems, allowing for a much more pervasive enforcement regime to push the culture toward compliance without the downsides of setting up lots of direct conflicts between irate drivers and law enforcement officers.)