BASIC REASONABLE AND PRUDENT STANDARD

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 vast majority of people behave in a “reasonable and prudent” manner.

It is also a practical standard because safe speed is a constantly changing variable. The safe speed for a 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 drivers as they encounter the myriad conditions inherent in each trip they take.

THE STATE MAY SIDE-STEP THE REASONABLE AND PRUDENT STANDARD

Having made this logical, scientifically defensible “reasonable and prudent” definition for maximum safe speed, legislative bodies may set arbitrary speed limits by statute and declare that statutory limits are reasonable and prudent.

This legalistic definition has nothing to do with whether or not any statutory speed limit is based in scientific principles. It merely provides a legal basis for enforcing statutory speed limits.

    As a matter of fact, scientific studies have shown that statutory limits are almost always lower than the scientifically based maximum reasonable and prudent speed for most motorists—in the vast majority of cases, the stated claim that statutory limits are reasonable and prudent is scientifically fictitious.

     Thus, government agencies "giveth and taketh away" this permission to drive at reasonable and prudent speeds. In one passage, they 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 maximums.

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. Apparently this has happened with respect to speed limits that are lower than safe, reasonable and prudent maximum speeds.

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. These 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 studies of human behavior.

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

Lawmakers and government administrators 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 state-imposed limits in order to avoid driving at excessive speeds.

In spite of the fact that this assumption is contradicted by the 1992 study and the excellent safety record of drivers who choose to drive faster than speed limits, lawmakers and government administrators set speed limits that are lower than the reasonable and prudent speeds chosen by the vast majority of drivers.

Lawmakers should also note that speed limits are tied to the rights of personal freedom guaranteed by the Constitution of the United States. The State should not limit the rights of individuals to choose reasonable, safe driving speeds.

   TYPICAL DRIVERS ARE CAPABLE OF CHOOSING SAFE SPEEDS

Extremely low traffic fatality rates show that the vast majority of drivers have a natural sensitivity to the physical laws that affect their safety. 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 adjust their speed accordingly.

For the most part, 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 legal speeds.

Engineering studies have determined that in the vast majority of cases, an appropriate value for the reasonable and prudent standard is the 85^th percentile speed in normal traffic flow.

This Section is quoted below.

Section 2B.13 Speed Limit Sign (R2-1)

Standard:

After an engineering study has been made in accordance with established traffic engineering practices, the Speed Limit (R2-1) sign (see Figure 2B-1) shall display the limit established by law, ordinance, regulation, or as adopted by the authorized agency. The speed limits shown shall be in multiples of 10 km/h or 5 mph.

Guidance:

At least once every 5 years, States and local agencies should reevaluate non-statutory speed limits on segments of their roadways that have undergone a significant change in roadway characteristics or surrounding land use since the last review.

No more than three speed limits should be displayed on any one Speed Limit sign or assembly.

When a speed limit is to be posted, it should be within 10 km/h or 5 mph of the 85th-percentile speed of free-flowing traffic.

Following is a technical discussion of intricacies in the wording of the MUTCD text, which may allow inappropriate speed limits to be set at the insistence of governing agencies or the application of flawed engineering judgment. If the reader would rather bypass this technical discussion, skip to the paragraph beginning with “An informative brochure”.

The word, “Standard”, preceding the first paragraph in Section 2B-13 indicates that the following paragraph is a mandatory requirement. Thus, an engineering study is required for each speed limit before a valid speed limit sign can be posted.

The last phrase in this first paragraph, “shall display the limit established by law, ordinance, regulation, or as adopted by the authorized agency.” concedes the final decision to the governing agency that has adopted a speed limit for the location.

This means that the governing agency has final control and that, after an engineering study is concluded, speed limits are subject to their decision. This permission can create problems when the governing agency insists on posting a speed limit lower than indicated by a valid engineering study.

A further consideration that can lead to inappropriate speed limits is the allowance for engineering judgment to override strict interpretation of MUTCD requirements.

MUTCD Section 1A.09 Engineering Study and Engineering Judgment

Standard:

This Manual describes the application of traffic control devices, but shall not be a legal requirement for their installation.

Guidance:

The decision to use a particular device at a particular location should be made on the basis of either an engineering study or the application of engineering judgment. Thus, while this Manual provides Standards, Guidance, and Options for design and application of traffic control devices, this Manual should not be considered a substitute for engineering judgment.

Engineering judgment should be exercised in the selection and application of traffic control devices, as well as in the location and design of the roads and streets that the devices complement. Jurisdictions with responsibility for traffic control that do not have engineers on their staffs should seek engineering assistance from others, such as the State transportation agency, their County, a nearby large City, or a traffic engineering consultant.

It is important to note that the MUTCD is an engineering manual that allows for engineering judgment when applying its specifications and recommendations. This allowance is very important as conditions vary from place to place. We must necessarily rely on good engineering judgment to adjust the published recommendations when necessary.

This permission must not however, be used as an excuse by government agencies for failure to apply appropriate MUTCD specifications—especially not with respect to speed limit signs. The critical matter of speed control deserves the best possible effort from all concerned. Unwarranted departures from the MUTCD must not be allowed.

Government agencies should stand back and accept the results of engineering studies required for each speed limit. While it may be appropriate for government agencies to mandate certain speed limits, they should be high enough to allow the results of engineering studies to control posted speed limit values.

Any government agency that insists on a speed limit that is 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 eighty-five percent or more comply with the posted speed limit. Ongoing speeds faster than the 85^th percentile would likely be prima-facie evidence that the speed limit is too low.

Setting speed limits in accordance with MUTCD standards and recommendations would go a long way toward avoiding the problems discussed in this web site. One of the key results would be that at least 85% of motorists passing a speed limit sign would comply with the limit.

Very few speed limit signs are posted at a value at which 85% or more of passing motorists comply with the limit. This is compelling evidence that government agencies throughout the United States have posted the vast majority of speed limits lower than the 85^th percentile recommended in the MUTCD.