THE HUMAN ELEMENT

    Much is said about the incompetence of typical drivers. Although they are the butt of many jokes and can be a pain-in-the-neck to fellow motorists, how much of this negative perception is justified? How competent are typical drivers in managing their automobiles?

Let’s look at some scientific facts.

The following chart shows the relationship between the fatality rate and speed limits in the state of Utah. Except for numerical values, this chart is representative of conditions in virtually all other states.

Fatality Data Provided by National Highway Traffic Safety Administration

Normal Traffic Speed Has Increased by Approximately 0.40mph per Year from 1974 to 2009

The following conclusions are drawn from the chart.

1.    Contrary to expectations, when the 55 mph national speed limit was imposed the fatality rate unexpectedly increased after an initial decline and did not return to the original level for approximately five years.

2.    Except for erratic behavior during the years immediately following 1974, the fatality rate declined 68% from 3.42 to 1.06 fatalities per hundred million miles traveled between 1974 and 2009.

3.    On Utah freeways, the 85^th percentile speed  has increased from approximately 65 mph in 1975 to approximately 82 mph in 2009, which is equal to 0.4 mph per year.

4.    There appears to be no direct relationship between freeway speed limits and traffic fatality rates in Utah. 

SPEED LIMITS DO NOT AFFECT SPEED OF TRAFFIC

To emphasize points made earlier: The already mentioned 1992 study completed by the Federal Highway Administration along with others clearly show that:

1.    Increasing speed limits does not produce faster traffic speeds. With very few exceptions, motorists select safe, “reasonable and prudent” speeds at which they are comfortable. If they read a speed limit that they believe is too fast, they drive more slowly.

2.    Lowering speed limits does not produce slower traffic speeds. When motorists read a speed limit sign that they believe is too slow, they drive at a faster speed they consider comfortable and safe.

3.    As presently used, speed limits are basically irrelevant.

Motorists do not accept them as useful information when choosing the speed at which they drive. 

MODERN TECHNOLOGY ALLOWS MOTORISTS TO DRIVE SAFELY AT HIGHER SPEEDS

Technological improvements in highways and automobiles have allowed motorists to travel safely at ever faster speeds. For those who can remember driving on the highways of the 60s and 70s, the improvement in safety of current highways and vehicles is striking.

MOTORISTS ADJUST SPEED TO SAFE, COMFORTABLE LEVELS

In the great majority of cases, motorists intuitively adjust their speed to a safe, comfortable level for existing conditions. They take into consideration such factors as vehicle capability, adverse weather conditions, road conditions, and construction activities.

The excellent safety record of the motoring public stands as compelling evidence that individual drivers really do choose safe speeds albeit with little regard for posted speed limits. So, why is there so much confusion and angst in managing this very important traffic safety component?

MISLEADING REPORTS

Publications concerning traffic safety 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 statistical studies by including percentage figures of the number of deaths, injuries, fatalities, etc. due to speed and may foster  misunderstanding of the role of speed in traffic safety.

Such reports are fatally flawed as statistical studies when these parameters are not defined because they merely state the obvious: Speed is always present in every crash because a crash cannot occur unless one or more vehicles are in motion. Therefore it can accurately be said that speed is a "factor", "contributes to", or "is related to" all crashes.

Statements of this type may be more like advertising copy that is carefully designed to leave a general impression (even a false impression) that is more in the interest of the advertiser than the reader.

In order to develop statistical data from which valid decisions can be made, all parameters must be precisely defined and data collection must be performed by carefully trained individuals who all use the same methods. Unfortunately, these controls have not been included in many reports that have been used as a basis for speed limit policies resulting in poor decisions when setting speed limits.

     The presence of any of these phrases in a report that does not contain a specific definition for speed and does not describe strict data collection methods is a tip-off that the report probably is not statistically sound and should be disregarded.

SPEED LIMIT MYTHS

INAPPROPRIATE GOVERNMENT ACTION

Government officials may be confronted by neighborhood groups expressing concern 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 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 significantly improve traffic safety while generating similar revenues.

The process of setting appropriate speed limits is a technical matter and should be carried out only by qualified traffic engineers. Government agencies responsible for traffic regulation should consult traffic engineers and respect their advice.

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