Fair Traffic Laws
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The State has a solemn responsibility to create traffic regulations that define proper driving conduct and allow for penalizing those who do not operate their vehicles in a reasonable and responsible manner. After appropriate traffic regulations are in place, the State must develop effective education and enforcement programs. 

The test for success in this responsibility is whether or not the great majority of motorists voluntarily comply with traffic regulations. If they do not, the State may have imposed unreasonable regulations or its education and enforcement programs may not be working.


Fair traffic laws must:

1.    Reflect the reasonable behavior of motorists.

2.    Provide useful information so that drivers can make good decisions.

3.    Be enforceable.

4.    Foster voluntary compliance by the majority of motorists.

Let’s see how presently posted speed limits stack up to these requirements.

1.    Do current speed limit laws reflect the reasonable behavior of motorists?

No—Although the great majority of drivers choose to drive significantly faster than most speed limits, they are reasonable drivers choosing reasonable speeds as evidenced by extremely low fatality rates.

2.    Do current speed limits laws provide useful, accurate information?

No—Speed limit signs cannot provide accurate information for all drivers at all times because they are static devices that cannot reflect the dynamics of normal vehicle speeds.

This inherent problem is compounded by the practice of posting unrealistic speed limits that are lower than truly reasonable, maximum safe speeds. As a result, motorists cannot rely on speed limits to provide information useful in determining their maximum safe speed.

3.    Are current speed limit laws enforceable?

Not Really—Webster's definition of enforcement is "to make sure that people do what is required by a law". 

Considering the fact that fewer than 1% of speed limit violators are cited, it appears that it is not feasible to enforce present speed limits to the extent necessary to "make sure" that all drivers  obey them.

4.    Do current speed limit laws foster voluntary compliance??

No—The great majority of motorists drive safely at speeds significantly faster than posted speed limits. Voluntary compliance is almost nonexistent.

      Clearly, as presently employed, speed limits fail the fair traffic law test. Motorists are safe when traveling at speeds significantly faster than posted speed limits and governmental agencies have no moral right to penalize them for this reasonable behavior.


      Traffic codes typically define speeding violations as speeds that are not "reasonable and prudent" under existing conditions. This reasonable standard rests on the valid presumption that the great majority of people behave in a “reasonable and prudent” manner.

       It is also a practical standard because the reasonable and prudent speed for each driver depends upon their driving skill, the condition of their vehicle, the type and condition of the roadway, weather, traffic, and many other factors. Reasonable decisions concerning traveling speed can only be made by individual drivers as they encounter ever-changing conditions in each trip they take.



 Having stated this logical, scientifically defensible “reasonable and prudent” definition in their motor vehicle codes, jurisdictions may mandate unrealistic speed limits and declare by statute that they are “reasonable and prudent”. This legalistic definition has nothing to do with whether or not any speed limit is based on scientific principles. It merely provides a legal basis for enforcing statutory speed limits.

Many studies have shown that present statutory limits are almost always lower than scientifically-based maximum safe speeds. In the majority of cases, the claim that statutory limits are reasonable and prudent is scientifically fictitious.

Thus, government "giveth and taketh away" this permission to drive at reasonable and prudent speeds. In one passage, it may allow the reasonable and prudent standard only to effectively cancel it in a later passage by stating that lower statutory limits are reasonable and prudent. 



There is a great difference between statutory and scientific laws. Statutory laws are made by governing bodies to regulate human activities whereas scientific laws are based on the immutable laws of physics.

In democratic societies statutory laws represent a consensus arrived at after discussion and debate by a governing body. The motives of participants in the debate are based on many factors—some honorable and well-founded, others based in selfish self-interest, ignorance, or misunderstandings. Under these conditions the legislative process may produce bad laws that impose injustice and hardship on the public.

Scientific laws suffer from none of the arbitrariness inherent in statutory laws. Scientific laws are based in physics and represent how the universe works. These laws cannot be tampered with—no governing body can adjust the law of gravity or any other law of physics. Scientific laws are what they are and man must learn to work within their constraints.



It is critical that statutory laws are consistent with applicable scientific laws and reasonable human behavior or serious problems are sure to develop. Unfortunately, many legislators, government officials, and members of influential special interest groups are not scientists and, when they develop statutory laws, they do not properly consider scientific facts and normal, responsible human behavior. 

The beginning point for much of the confusion regarding speed limits may lie in the physical relationship between vehicle speed and kinetic energy: Kinetic energy increases twice as fast as speed.

     Realizing the devastating impact of excessive speed on crash severity, lawmakers rightly believe that it is very important to restrain vehicle speed to a reasonable level.

At this point, lawmakers may make a leap of faith and assume that motorists need government-imposed speed limits in order to avoid driving at excessive speeds and that posting speed limits will accomplish this goal.

Although this assumption is contradicted by the 1992 study and many other scientific studies as well as the excellent safety record of drivers who choose to drive faster than speed limits, lawmakers may set unrealistic speed limits.



Engineering studies have determined that in the great majority of cases an appropriate value for speed limits meeting the reasonable and prudent standard is the 85th percentile speed in normal traffic flow. As mentioned earlier, this speed is also the safest speed in normal traffic.

When a speed limit is set according to the 85th percentile criterion, 85 percent or more of the drivers on that roadway comply. All others, except those few who drive dangerously fast, exceed speed limits by no more than a few miles per hour.

Speed limits set lower than the 85th percentile may produce the following perverse effects:

1.     Interfering with coordination of vehicles by encouraging drivers to impede traffic.

2.     Denying motorists the right to drive at the safest speed.

3.   Authorizing enforcement agencies to issue speeding tickets to safe drivers who are driving safely.

     Without question, the speed limit is important when dealing with drivers who drive at dangerous speeds. However, in order to avoid penalizing safe drivers, speed limits must allow safe speeds chosen by the majority.

Any government agency that insists on a speed limit lower than the 85th percentile of the normal speed of traffic should be willing to devote whatever resources are necessary to reduce the speed of traffic at that location so that 85 percent or more comply. Ongoing speeds faster than a posted speed limit would indicate that the process of setting the speed limit was flawed or the agency is not truly committed to enforcing its laws.


The process of setting speed limits consistent with the "Reasonable and Prudent" standard is best handled by competent traffic engineers. Departments of transportation in several states have published informative brochures describing how speed limits are scientifically determined. For example, see "Establishing Speed Limits" published by the Arizona Department of Transportation. Click here to read "Establishing Speed Limits".

Unfortunately, the task of setting speed limits often succumbs to political expediency as legislators and other government officials bypass or override engineering recommendations and mandate unrealistic speed limits.




A speed trap is a roadway posted with a speed limit lower than the maximum speed chosen by the majority of reasonable, prudent, safe drivers who regularly travel the roadway.


A speed trap allows enforcement officers to issue speeding tickets to safe drivers who are driving safely.



      When unrealistic speed limits are posted lower than the 85th percentile, a speed trap may be created allowing government to collect fines from safe drivers who are driving safely. This is morally wrong, totally unacceptable in a free society, and should not be allowed.

The current practice of issuing speeding tickets to safe drivers who are driving safely could be virtually eliminated if speed limits were set scientifically so the majority of drivers consider it hazardous to exceed them. On the other hand, speed limits must also be low enough to serve their purpose as a basis for citing drivers who drive at truly dangerous speeds. 

So, why is there so much confusion and angst in managing this very important traffic safety factor?


Traffic safety reports and other publications may emphasize the risk of speeding by declaring that speed is a "factor", "speed contributes to", or "speed is related to" crashes, injuries, deaths, etc. These publications may masquerade as official statistical studies by reporting a number or percentage of deaths, injuries, fatalities, etc. due to speed.

Such statements contribute nothing to a report because they merely state the obvious. Speed is present in every crash because a crash cannot occur unless one or more vehicle is in motion. Therefore it can truly be said that speed is a "factor", "contributes to", or "is related to" all crashes and the use of these terms may create unjustified emphasis on the importance of vehicle speed in traffic safety. 

This type of statement is called a"deepity", which although it is true, it is trivial and may lead to a falsehood such as the durable but false slogan, "Speed Kills". The pernicious result of accepting this slogan as fact is that it may misdirect attention from the true causes of crashes and misguide corrective action. 

Deepities are in the same class as advertising copy: Carefully designed to create a general impression (even a false impression) that is more in the interest of the advertiser than the reader.

     The presence of any of these phrases in reports regarding vehicle speed is a tip-off that the report may not be statistically sound and should be disregarded.

In order to develop statistical data from which valid decisions can be made, all parameters must be precisely defined and data must be collected by carefully trained individuals who all use the same or equivalent methods. Unfortunately, these controls have not been included in many reports that have been used to justify speed limit policies.


Agencies responsible for setting speed limits may be confused by the following speed limit myths:

1. Speed limits are necessary to assure that traffic flows at safe speeds.

2. Posting a lower speed limit will reduce the speed of traffic.

3. Because most motorists drive faster than posted speed limits, it is necessary to set speed limits lower than the normal speed of traffic.

There is much evidence that these myths have a virtual stranglehold on traffic safety action groups and government agencies, creating a strong tendency to set unrealistic speed limits. 


Government officials may be confronted by neighborhood groups concerned that traffic in their neighborhoods is too fast. These officials may react by lowering speed limits in the misguided belief that traffic will flow more slowly. While this response may mollify a few citizens, it does not solve their problem when traffic continues to flow at the same speed as before.

Then there is the indefensible practice of operating speed traps as a source of revenue for community coffers. Under present speed limit posting practices, government can quickly raise money by assigning officers to enforce speed limits at almost any location in the country.

A tragedy of this practice is that if enforcement were shifted from speed limits to coordinating laws, the same enforcement effort may generate similar revenues while significantly improving traffic safety.


Many motorists accept speeding citations as an unpleasant, almost unavoidable, fact of life. Although they may know they were driving safely when cited for speeding, rather than spend time to contest a speeding ticket, they simply pay up and hope that their luck is better in the future.


We need to correct these problems, which have persisted for many years. If government will not take effective action on its own, a grass-roots movement may be needed wherein the driving public recognizes the extent of unjustified speeding citations and takes action to correct the problem. See the "Implementing Changes" page on this website.

The next page contains information concerning possibly the most useful speed management sign: The Advisory Speed Sign.

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