Does it make sense to strictly enforce a 20 or 25 mph limit in areas with residential/pedestrian traffic? Certainly, especially given that pedestrians crossing a street are essentially at a 25 mph speed difference relative to perpendicular traffic. But if we apply this arithmetic to semi trailers traveling at 65 mph on the highway, a 25 mph difference would suggest a speed limit of 90 mph, even neglecting the safety difference in a vehicle-vehicle collision.
Where are most current speeding tickets issued? Is it in low-speed, residential areas where drivers know that an extra 5 mph won't save them any time at all (and would greatly increase the risk of injury in an accident)? Or is it in high-speed straights on the highway where an extra 15 mph can save you hours on long trips (where a speed limit effectively grandfathered from the malaise era still applies)?
Another consideration: if speed enforcement on highways was so critical to public safety, why are radar detectors and even laser jammers legal in many US jurisdictions? My perception is that physics-based policy decisions never get far in the US system. Ultimately, automated enforcement/better technology seems orthogonal to the policy problem. We should get the policy right first.