A soon-to-be-released report produced by the University of Minnesota in cooperation with the Minnesota Department of Transportation concludes that “during [a period of enhanced speed enforcement] there were reductions in the numbers of Fatal and ‘A’ Injury Crashes.” (Harder 2007) That’s great, right? Fewer people dying is good for everybody, morticians excepted.

Trouble is, the data showing a decrease in casualties is a bit sparse, and the study fails to establish a causal relationship between enhanced enforcement and fewer fatalities. Specifically, the bad crashes decreased in number in both the enhanced and regular enforcement zones. Was there a halo effect? Did cars get safer? A similar argument could be made about the implied correlation with speed and the lack of supporting data.

The report openly acknowledges that “an increase in the variability in speed … is often associated with increases in crash rate.” In other words, it’s not necessarily absolute speed that’s a problem, but rather the relative speed between cars. Data varied, but the study showed that generally less than 65% of drivers in the study areas were within the 10 mph pace.

Perhaps we’re going about speed enforcement the wrong way. Instead of setting an absolute limit, maybe we should post a suggested speed. Officers would monitor the average speed of the traffic and note outliers. Individuals who are not within +/- 5 mph of the mean speed would receive a citation.

With that system, the differential speed would be reduced, which in turn would decrease the crash rate. People could drive faster than present limits as long as everybody else travels at a similar speed. Likewise, people going far slower than the flow, thus presenting a hazard, could be cited.

I like it.