Speed Limit Fact Sheet ( PDF )
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By James J. Baxter, NMA Founder

There comes a time when you know too much about a subject. A sure sign of this happening is when you’re no longer able to answer a simple question on that subject without confusing the questioner. I’ve come to that point when it comes to talking about speed limits and their effect on highway safety.

The signs are all there. Reporters that get a blank stare on their faces when I state our position. Interviewers that ask the same question six times and still don’t grasp the answers. And, quotes in newspaper articles that don’t remotely reflect what I said. It’s tempting to blame the “messenger,” but I’m the one with the message to sell and it ought to be packaged up in a way anyone can quickly grasp it.

I suspect I am not the only NMA spokesperson with this problem. I’ve given this a lot of thought and the following is my attempt to boil down certain basic truths, concepts, and arguments to their essential elements. Some of these topics have broader application than just speed limits.

Fatalities versus fatality rates.
Our opponents frequently use raw fatalities to bolster their arguments in favor of anti-motorist regulations. These are usually large numbers which impress the ill-informed and the ignorant. They are also relatively useless when it comes to analyzing trends or “cause and effect” relationships.

Fatality rates based on 100 million vehicle-miles traveled (vmt) are the more legitimate way to measure trends and “cause and effect” relationships. Here’s a simple way to explain this to a reporter or legislator. If we took 100 people who averaged 10,000 miles per year and the group experienced two fatalities, we would have a FATALITY RATE of “2” per one million miles travelled. If we doubled the number of people who also drove 10,000 miles and all else was equal, we would probably see 4 fatalities, but the fatality rate would remain at “2” per one million miles travelled.

Our opponents would argue that the world is about to end we have just experienced a 100% increase in highway fatalities! Of course this is nonsense and any reasonable person would recognize that fact.

Our highways are becoming more dangerous, especially with higher speeds.
In the early 1920’s, our highway accident fatality rate was estimated at 25 per 100 million vehicle miles traveled. If that rate prevailed today, we would experience 700,000 motor vehicle fatalities a year! Tell me we haven’t made dramatic improvements on the highway safety front! Nevertheless, the self-appointed safety establishment persists in using fluctuations in annual fatalities to support their contentions. If the fatalities go up, it’s because motorists aren’t heeding their advice. If the fatalities go down, it’s because their latest campaign was such a great success. In reality, most “safety campaigns” have little material impact on the rise or fall in fatalities.

I have said this before, but it merits repeating: The overwhelming cause of the tremendous reduction in the highway fatality rate is better vehicles and better highways. Consider this single example. In the 1930’s, one-third of all fatal accidents were attributed to vehicle equipment failure, usually tires or brakes. Today, only one to two percent of fatal accidents relate to an equipment failure. Similar results can be witnessed when comparing the fatal accident rates on modern Interstates and the old two-lane highways they replaced.

Speed limits can and should be used to control overall traffic speeds.
This myth haunts us like bad breath after a night of beer, pizza, and cigars. Speed limits have virtually no influence on regulating general traffic speeds. The only legitimate function of speed limits is to delineate at what point reasonably competent drivers exceed the safe speed for a given roadway. If the speed limit is properly set, it can serve as a useful form of information as well as a “trigger” for enforcement action. The speed limit will only function if it is set to reflect prevailing speeds. For too long we have suffered under the cart before the horse illusion that speed limits can dictate prevailing speeds. We have just concluded a 22-year-long experiment that has unequivocally proven that speed limits do not determine traffic speeds.

Forty years of brainwashing have made it exceedingly difficult to make this distinction clear and understandable. Rural speed limits did not come into wide use until after the Second World War. The early motivation was largely a desire to curtail true “high flyers” and to take some of the subjectivity out of speed enforcement. Reasonable and prudent has great allure until the local sheriff decides anything over 45 mph is imprudent. Motorists wanted a benchmark almost as bad as did the police and the courts.

The ensuing expansion of speed limits was not a smooth and seamless process, but from it came research that is just as valid today as it was in the 1950’s. The vast majority of drivers can be expected to travel at safe and reasonable speeds, regardless of posted speed limits. The faster group of drivers, still driving at reasonable speeds (i.e. the 85th to 90th percentile), will experience the fewest accidents per mile driven. Those drivers traveling significantly slower or significantly faster than the 85th percentile group experience far more accidents.

Here’s the message to drill home:
Speed limits should be based on the highest travel speeds of the vast majority of safe and reasonable motorists. The reverse, attempting to dictate travel speeds through the use of speed limits, has not and will not work, and will, in all likelihood, diminish traffic safety.