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

The question, “Do speed limits matter?” hardly seems worthy of an answer. Insurance companies, police agencies, state transportation departments, and national safety organizations would have us believe that speed limits are a critical component of traffic regulation. Without those numbers on the signs and radar-wielding highway patrols, the entire system would self-destruct.

This belief is based on several dubious precepts, none of which have ever been proven or justified.

The most basic of these precepts is that motorists, in the absence of speed limits, will drive in a manner that ignores their own welfare and that of fellow highway users. That without speed limits, they would drive at reckless irresponsible speeds without concern for the consequences. Does that sound like you and the people you know?

Another piece of speed limit folklore is that posted speed limits, given reasonable enforcement, can dictate traffic speeds. By extension, it is implied that raising or lowering posted speed limits will change the speed of traffic in that area. This notion has been thoroughly disproved on several occasions but the myth persists.

“Speed Kills” and “Slow is Safe” are well-entrenched slogans that have no basis in fact. Repeated long enough and loud enough, these slogans have taken on the aura of “truths.”

I know what you are thinking, “This guy is blowing smoke in my ear. He doesn’t know what he’s talking about.” Stay with me for a bit longer and maybe I can change your mind, or at least bring about a little skepticism when one of those Public Service ads floats across your T.V. screen extolling the virtues of speed limits.

Let’s first look at the premise that drivers will go berserk if they are not confined by speed limits.

Only one industrialized country officially allows unlimited speeds on portions of its public highways, Germany. Significant stretches of the Autobahn do not have speed limits. Yes, some vehicles travel at very high speeds, some in excess of 150 mph! But, the average speed for most vehicles is around 80 mph, about 10 mph faster than traffic in the U.S. on comparable highways. But, here’s the clincher, the fatality rate on the German Autobahn is lower than the fatality rate on rural Interstates in the United States!

Lest you think this is the product of Teutonic discipline and training, keep in mind that a large portion of the traffic on German highways originates in several other countries. Despite the cultural and language differences, there is a common understanding of a few basic rules: pass on the left, yield the left lane to faster traffic, and pay attention to your driving. It really works well.

Do speed limits dictate travel speeds? Not much. Speed limits, backed up with intense enforcement, can retard traffic speeds, at least in the short term. However, the national 55 mph speed limit proved the folly of trying to use speed limits to slow traffic.

Let’s clear up one major misconception: Speed limits do not regulate traffic speeds; they never did and never will. Properly applied, speed limits should reflect the speed of the large (and safe) majority of vehicles using the highway. Keep in mind that millions upon millions of cars pound up and down our roads day in and day out, without having accidents. Except for a few vehicles, these cars are obviously traveling at speeds that are within reason. You say, “Aha, got you there. Those cars are going at reasonable speeds because they’re being restrained by speed limits and the enforcement of those limits.”

Let me tell you about the most recent and most exhaustive federal study on this very subject.

Over a period of five years, researchers monitored motorist response to speed limits at 227 different locations around the United States. First, motorist speeds were measured at all the locations. Next, the speed limits were raised on some roads and lowered on others while yet others remained the same. The results? Speeds did not change. People continued to drive at speeds that they felt were comfortable and safe, just like you and I do.

This study also measured the relationship of speed limit changes and accident frequency. As you might expect, if speeds didn’t change much, neither did accident rates. However, in those instances where speed limits were raised, there was a slight reduction in accidents. Could it be smoother traffic flow?

Is slower really safer? Not on our rural highways it isn’t. Again, federal and state studies have repeatedly shown that the folks most likely to get in an accident are the ones driving at speeds significantly below the average speed of traffic. In fact, the safest motorists, in terms of avoiding accidents, are those who are driving 5 mph to 10 mph above the average speed of traffic.

You have probably seen those insurance company ads bemoaning the carnage and higher rates sure to follow, if speed limits are raised on rural highways. Do you know what percentage of all accidents occur on highways posted at 65 miles per hour? The answer is 2 percent. The insurance industry would have you believe that an increase of two miles per hour in traffic speeds (the increase that occurred when speed limits were increased from 55 mph to 65 mph on rural Interstates), will set highway safety back at least a millennium and end civilization as we know it.

One of the most repeated and believed myths concerning speed limits goes like this, “You should keep the speed limit low because no matter where you set it, “they” (whoever “they” are) will always drive 10 miles over the limit.” This is sheer nonsense, but it persists like the odor in a little kid’s tennis shoes.

In 1973, when we had a 75 mph speed limit on the rural Interstates in 10 different states, there was 90 percent or better compliance with the speed limit in those states. The states that had 70 mph limits had around 80 percent compliance and the states with 65 mph speed limits had approximately 60 to 70 percent compliance. In 1994, New York measured motorist compliance with its 55 mph speed limit on rural Interstates. The result: 4 percent of the motorists were obeying the speed limit. Do you see a pattern here?

Whenever I’m confronted with the “they’ll always drive 10 miles over” argument, I always ask, “If the speed limit was set at 100 mph would you then drive 110?”

If you’ve moved in my direction at all you might ask, “Do speed limits have any value at all?” Yes they do, but only if they’re established in the right way for the right reasons.

The right reasons include informing the normally competent motorist about what is a safe and efficient speed for a given highway when there are good travel conditions. A second reason is to establish a speed limit that expedites smooth and harmonious traffic flow, in this instance a target that most vehicles should try to emulate.

Multi-lane limited access highways can tolerate a great deal of speed variance, as long as there is good lane discipline. Two-lane highways, at the other extreme, function best with uniform vehicle speeds. Properly set speed limits can accommodate these different circumstances.

Traffic engineers have repeatedly rediscovered that the best way to set speed limits is to measure the free-flowing speeds of traffic and determine the 85th percentile speed, which is the speed at which 85 percent of the vehicles are traveling at or below. With an 85th percentile speed limit, a 5 mph enforcement tolerance, and the unique phenomenon where faster traffic actually slows in the presence of reasonable speed limits, we will have 95 percent compliance with the speed limit. Compare those numbers with New York’s 4 percent compliance.

Do speed limits matter? Yes they do. Today they generate millions of pointless traffic tickets and billions of dollars of undeserved insurance surcharges, disrupt traffic flow, increase congestion, and have created a siege mentality among those who frequently use our public highways.

It doesn’t have to be this way. We can have rational traffic regulation, including appropriate speed limits, that will expedite traffic, improve safety, and focus enforcement efforts toward those motorists who clearly drive in a reckless or discourteous manner. All we have to do is demand that it be done.