SETTING FAIR, LEGAL, SPEED LIMITS

Reasonable 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.

No—Although the vast 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 limit 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 speed limits that are lower than true reasonable maximum safe speeds. As a result, motorists cannot rely on most speed limits to provide information useful in determining their maximum safe speed.

3.    Are current speed limit laws enforceable?

Not Really—Speed limits are enforceable only in the narrowest sense: They provide measurable values that can be used as a basis for citations.

Considering the fact that far less than 1% of speed limit violators are cited and voluntary compliance is essentially non-existent, it appears that enforcing present speed limits to the extent necessary to gain voluntary compliance is not feasible. 

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, speed limits, as presently applied, fail the reasonable law test. Motorists are safe when traveling US roadways at speeds significantly faster than posted speed limits and governmental agencies have no moral right to collect fines for this reasonable behavior. 

BASIC “REASONABLE AND PRUDENT” STANDARD

The current practice of issuing speeding tickets to safe drivers who are driving safely could be virtually eliminated if speed limits were set so the majority of drivers consider it risky 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.

Traffic codes typically define speeding violations as speeds that are not "reasonable and prudent" under existing conditions. This is an eminently reasonable standard resting 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 changes from moment to moment depending 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, reasonble drivers as they encounter the myriad conditions inherent in each trip they take.

THE STATE MAY SIDE-STEP THE “REASONABLE AND PRUDENT” STANDARD 

 Having stated this logical, scientifically defensible “reasonable and prudent” definition in their motor vehicle codes, responsible jurisdictions may mandate, unrealistically low 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.

As a matter of scientific fact, studies have shown that present statutory limits are almost always lower than scientifically-based reasonable and prudent maximum speeds. In the vast majority of cases, the stated 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. 

STATUTORY LAWS VS SCIENTIFIC LAWS

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.

STATUTORY LAWS MUST AGREE WITH SCIENTIFIC LAWS AND REASONABLE HUMAN BEHAVIOR

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, prudent human behavior. Although authorized to set traffic laws, they may not be qualified to do so. Apparently this has happened with respect to speed limits that are lower than safe, reasonable, and prudent maximum speeds.

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

Lawmakers and government administrators may cling to this scientific fact as the primary justification for setting speed limits. Realizing the devastating impact of excessive speed on crash severity, they rightly believe that it is very important to restrain vehicle speed to a reasonable level.

At this point, lawmakers and government administrators 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.

In spite of the fact that this assumption is contradicted by the 1992 study (as well as by many other scientific studies) and the excellent safety record of drivers who choose to drive faster than speed limits, lawmakers and government administrators often set speed limits that are lower than the reasonable and prudent speeds chosen by the great majority of drivers.

TYPICAL DRIVERS ARE CAPABLE OF CHOOSING SAFE SPEEDS

As mentioned earlier, extremely low traffic fatality rates show that the great majority of drivers have a natural sensitivity to the physical laws that affect their safety. For the most part they accurately evaluate the effect of speed when their vehicle approaches curves or road irregularities, bad weather, congested traffic, work zones, and many other situations and appropriately adjust their speed.

With some exceptions, typical drivers are fully capable of choosing safe driving speeds—their behavior is the “reasonable and prudent” behavior alluded to in traffic codes as the primary basis for speed limits.

THE 85^TH PERCENTILE SCIENTIFIC ENGINEERING STANDARD

Engineering studies have determined that in the great majority of cases, for each speed limit an appropriate value for the reasonable and prudent standard is the 85^th percentile speed in normal traffic flow. Speed limits set lower than the 85th percentile may create the perverse result of  interfering with coordination of vehicles in normal traffic flow, increasing the variation in the speed of vehicles, and requiring drivers to drive slower than the safest speed.

When a speed limit is set according to the 85^th percentile criterion, 85 percent or more of the drivers on that roadway will comply. All others, except those few who drive dangerously fast, will exceed speed limits by no more than a few miles per hour. Although other factors may justify departure from the 85^th percentile value, it is by far the most suitable basis for most speed limits.

Without question, speed limits are important when dealing with drivers who drive at dangerous speeds. In order to avoid trapping safe drivers, however, speed limits must be high enough to include the speeds chosen by the majority. Speed limits set at the 85^th percentile and enforced with an allowance of 5mph may accomplish this goal and also be low enough to identify dangerous drivers.

SCIENTIFIC ENGINEERING STUDIES ARE REQUIRED TO ESTABLISH FAIR SPEED LIMITS

The process of setting fair speed limits that are consistent with the "Reasonable and Prudent" standard is best handled by competent traffic engineers. Departments of transportation in several states have published informative brochures dealing with how speed limits should be determined. For example, see "A Case of Majority Rule" published by the Arizona Department of Transportation. Click here to read "A Case of Majority Rule".

Unfortunately, the task often succumbs to political expediency as legislators and other government officials, who are authorized but may not be qualified to set speed limits, bypass or override engineering recommendations and mandate unrealistic speed limits.

Any government agency that insists on a speed limit lower than the 85^th 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 to the point that 85 percent or more comply. Ongoing speeds faster than a posted speed limit would likely be prima-facie evidence that the process setting the speed limit is flawed or the agency is not truly committed to enforcing its laws.

SPEED TRAP DEFINED

Definition

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.

Corollary

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

FAILURE TO FOLLOW SET SPEED LIMITS SCIENTIFICALLY CREATES SPEED TRAPS

When speed limits are posted lower than the 85^th 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.

CORRECTING THE PROBLEMS

We need to correct this egregious injustice, which has persisted for many years. Government agencies should post speed limits according to scientific traffic engineering studies.

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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