The Cato Institute, a libertarian think tank, released a report this week claiming that since speed limits went up nationwide in 1995, traffic deaths have declined. The full report can be downloaded at http://www.cato.org/pubs/pas/pa-346es.html. A more skeptical analysis of the numbers only proves that raising the speed limit from 55 to 75 miles per hour has not significantly increased traffic deaths on highways as initially feared. From the report:
Almost all measures of highway safety show improvement, not more deaths and injuries since 1995. Despite the fact that 33 states raised their speed limits immediately after the repeal of the mandatory federal speed limit, the National Highway Traffic Safety Administration reported last October that “the traffic death rate dropped to a record low level in 1997.” Moreover, the average fatality rate even fell in the states that raised their speed limits.
Evidence of a significant decrease is pretty slim. Especially since the data is only collected over a two year period. The numbers for 1995 and 1996 are about the same, and while the 1997 figures are lower they are within the expected statistical range. In other words, they may be just as likely a statistical fluke as a real decrease.
In real numbers, 1997 had 150 more highway traffic deaths than 1995 (41,967 and 41,817 respectively). When correctly adjusted for increased traffic, the numbers drop. Both 1995 and 1996 had 1.8 deaths per 100 million vehicle miles traveled, 1997 had only 1.7. This decrease is seen across the board, states that raised their speed limits showed just as much improvement as states that did not.
But, what if we adjusted the statistics differently. Instead of vehicle miles traveled, what if we adjusted by vehicle hours spent on the highway. Since people are driving faster, they are spending less time driving (we are using rural highways here, not urban freeways) to the tune of 200 million vehicle hours according to the Cato Institutes own report. When adjusted this way, deaths are going up! ( I do not know how much, I do not have an estimate of total vehicle hours). Just another example of how playing with statistics can prove anyone's point of view.
This, of course, does not address the fact that we are only dealing with 3 years of statistics. Three data points does not make a valid study. In another ten years, there might be enough data to decide this issue, until then I would not recommend raising speed limits any higher.
The moral of the story: So far, there is no evidence that changing the speed limit on Americas highways from 55 mph to 75 mph has any effect (positive or negative) on the number of traffic fatalities.
Ironically, on the same day this report was released, Montana -- which had no speed limit before -- set their highway speed limit to 75. Too many out of state drivers not aware that the law says reasonable speed, were driving like it was the Daytona 500. (Last time I was in Montana, I never drove faster than 65, but then I was driving a Geo Metro at the time. :^)