Fair Traffic Laws

The nation’s roadways are marvels of design and construction. Wide freeways cross the United States and local streets are generally well maintained. Rush-hour congestion is a way of life for many commuters, but by and large, the transportation system provides Americans with excellent facilities for safe, convenient, and rapid travel.

Hindering this progress, however, are inadequate or unfair traffic laws, ineffective enforcement practices, deficiencies in highway signage, and inappropriate behavior of some motorists. These factors cause unnecessary congestion and compromise safety.

A cooperative effort by government and the driving public could produce even greater efficiency and safety on our national roadways.

First, let’s take a detailed look at each item in the compliance survey.

1. Impeding Traffic in the Left Lane

2. Turn Signal Timing

3. Following Distance

4. Improper Lane Usage

5. HOV Lane Speed

6. Speed Limits

IMPEDING TRAFFIC

Motorists should not be allowed to impede traffic in the left lane on multi-lane highways because it creates serious safety problems:

1. Traffic accumulates in clusters when faster drivers are unable to pass because a slower motorist is cruising in the left hand lane. This encourages lane-shifting, which can be extremely dangerous when aggressive or foolhardy drivers jockey from lane to lane trying to find their way through a cluster. It is far better to allow these drivers a clear path in the left-hand lane where they can safely pass to be observed later by enforcement officers who can stop them for driving too fast.

2. The most serious safety problem created by impedance is that emergency vehicles cannot travel faster than the average speed of traffic. This means that injury crashes may convert to fatal crashes because emergency vehicles cannot arrive in time to render life-saving aid.

In addition to creating serious safety problems, impeding traffic is inconsiderate and annoying behavior. In other situations, most people consider it extremely rude to obstruct the free movement of others. Yet, they blithely impose this discourtesy on their fellow motorists.

TURN SIGNAL TIMING

Turn signals have been standard equipment in motor vehicles for many years but are rarely used properly. The common practice is to signal at the same time (or even after) beginning a lane-changing or turning maneuver.

A turn signal is useless unless it is given in time so that those who are affected by the maneuver can respond. Notifying others of lane-changing intentions is a matter of simple courtesy and contributes to safer travel by all.

FOLLOWING DISTANCE

It should be obvious to all drivers that following too closely increases the risk of a crash if the driver ahead brakes suddenly. Following distance should be long enough so that a following driver can avoid a collision by decelerating or moderate braking.

Although following too closely may lead to crashes, a more frequent result is a long-lasting “compression wave” ,which may form in the traffic flow.

When a driver brakes suddenly, drivers who are following too closely brake even more severely to avoid a collision. As these braking vehicles slow down, they pack together in a group. This causes vehicles approaching from behind the group to form a compression wave as they slow to the speed of the group while those at the front of the group resume normal speed.

The compression wave migrates backward through the traffic flow and may persist for an hour or more. Long after the incident that triggered the compression wave, motorists encounter slow moving traffic and can see no reason for the slowdown. These incidents unnecessarily slow traffic and waste everyone’s time.

Also, “cutting-off” incidents, one of the most annoying and dangerous acts, essentially disappear when drivers have enough room to easily enter the space between vehicles when changing lanes.

IMPROPER LANE USAGE

Slower vehicles on multi-lane highways should flow in right-hand lanes. With very few exceptions, passing should occur only in a lane left of vehicles being passed. When passing occurs on both sides of a slower vehicle, traffic flow is disrupted and the probability of a crash increases.

SPEED OF TRAFFIC IN HOV LANES

HOV (high occupancy vehicle) lanes are designed to encourage car pooling and provide faster travel when other lanes are congested.

Unfortunately, HOV lanes attract slow drivers who happen to have another passenger in the vehicle. Traffic backs up behind such drivers frustrating following motorists. This behavior also decreases travel speed and reduces the volume of passengers transported in the HOV lane.

Getting the maximum throughput on a multi-lane highway system is a complex problem. Unless HOV lanes are used properly, they may reduce rather than enhance the efficiency of the system.

COURTESY-BASED LAWS

Before we move on to the speed limit issue, let’s pause for a moment to note that the first five of the six items mentioned above involve simple acts of courtesy. Drivers who allow faster drivers to pass, signal early enough to give adequate notice, stay far enough behind others so that they do not feel threatened, use right-hand lanes when traveling more slowly than others, and maintain a reasonable speed in HOV lanes show courtesy and respect to their fellow travelers.

Therefore, laws governing these matters are based in common courtesy—they are “courtesy-based laws”. Motorists who break these laws forgo opportunities to show courtesy and respect to other drivers and run the risk of offending them—no one gains by going against these reasonable requirements. Instead, violators of courtesy-based laws reap a negative result from their behavior: Other drivers consider them thoughtless and inconsiderate.

As human beings, we are constantly faced with risk-reward situations. We know that, in most cases, we must take a risk in order to enjoy a reward. Common sense dictates that we will only take a risk if we believe that a reward will follow that is worth more than the the risk. That is, we pursue activities that will produce a net positive pay-off and avoid activities that would bring on a zero or negative pay-off.

As mentioned above, violating courtesy-based traffic laws produces no benefit. Rather, the result is likely to be negative when others perceive violators as uncaring and discourteous Therefore, with adequate enforcement, drivers would perceive a risk of being ticketed for violating these regulations, and would obey them voluntarily because they have nothing to gain by violating them.

Therefore the key to achieving voluntary compliance to courtesy-based laws is to expose drivers to a significant risk of being ticketed for violating them. Law enforcement agencies could produce this perception by conscientiously enforcing these laws. It is also essential that these laws are reasonable and fair—and enforceable. So our task of achieving voluntary compliance to these courtesy-based laws has two simple elements:

1. Provide fair, enforceable courtesy-based laws, and

2. Concentrate enough enforcement on these laws so that drivers recognize a significant risk of being cited for violations.

Note, however, that we have a very different situation with respect to speed limits.

SPEED LIMITS

The sixth item in the questionnaire, Speed Limits, is in a class of its own for the following reasons:

1. There is no underlying relationship between speed and courtesy; a driver who chooses to drive faster or slower than others may be as courteous as any other driver.

2. While there is no benefit in violating courtesy-based regulations, motorists may benefit from violating posted speed limits. E.G., they may save time or they may want to avoid the tedium of driving at an unnecessarily low speed.

This distinction between courtesy-based laws and speed limits is very important. It is both the key to voluntary obedience of courtesy-based laws and the answer to the problem of non-compliance to speed limits.

As mentioned above, most motorists believe that they benefit from violating the law, as long as it is safe to drive faster than speed limits.

Enforcement will not change this behavior as long as the risk of receiving a speeding ticket is smaller than the perceived benefit from exceeding speed limits. Thus, unless government is willing to apply overwhelming force, the vast majority of motorists will continue to choose comfortable, safe speeds regardless of posted speed limits.

SAFE SPEED AND THE LAWS OF PHYSICS

Safety is the overwhelming consideration when motorists choose vehicle speed.

The scientific fact that kinetic energy increases twice as fast as speed cannot be denied. When motorists double their speed, they have four times as much energy to deal with and crashes are four times more severe at twice the speed.

Therefore, the impact of speed on traffic safety is of utmost importance. Vehicle speed must be carefully considered by traffic managers and wisely controlled by motorists to assure safety on our highways. The speed limit was invented to help deal with this vital safety factor. It must be recognized, however, that speed limits are of little, if any, value in controlling the speed of traffic. Motorists intuitively choose speeds that they consider safe. Speed limits are a minor factor in their decisions.

As evidenced by low fatality rates, the vast majority of motorists make reasonable and prudent decisions when selecting the speed at which they drive. Therefore, an appropriate method of determining an appropriate speed for a speed limit is strikingly obvious: Observe the speeds driven by these reasonable and prudent drivers, note the maximum speed chosen by the vast majority, and use this information as the basis for setting speed limits. Speed limits based on these values notify motorists of the maximum speeds considered safe by the majority of drivers and will be voluntarily obeyed.

This is the scientific method for setting speed limits: Traffic engineers have determined that an appropriate speed limit is near the upper 85^th percentile of the normal traffic speed distribution, which means that only 15% of drivers would exceed speed limits set at this value.

It is obvious, however, to even the casual observer that far more than 15% drive faster than most posted speed limits. This is compelling evidence that most speed limits in the United States are set lower than this recommended value.

These low speed limits create lawbreakers of safe drivers and set up speed traps allowing enforcement officers to issue speeding tickets to safe drivers when they are driving safely.

We may ask ourselves, how can this be? What has happened to create such inequities? The answer is that government agencies responsible for traffic laws mistakenly believe that they can control traffic speed by posting speed limits.

The problem is that speed limits do not work as a device to control traffic speed—as mentioned above, motorists disregard them when selecting the speed at which they drive. If they believe that it is safe to drive at a speed faster than a speed limit, they drive faster—if they believe that it is not safe to drive as fast as a speed limit, they drive more slowly.

This nonchalance regarding speed limits was identified in a landmark scientific study completed in 1992 by the Federal Highway Administration. The study conclusively shows that there is no significant relationship between the numbers on speed limit signs and the speed of traffic. Click here to read the study.

In spite of this compelling evidence to the contrary, government agencies responsible for traffic laws mistakenly assume that setting speed limits will help to manage traffic speed. Having been granted authority to set speed limits but usually, lacking qualifications to do so, they often mandate inappropriate speed limits that abuse the public and create other problems.

The process of setting proper speed limits is a complex, technical matter and should be carried out only by qualified traffic engineers. Unfortunately, in many jurisdictions traffic engineers are seldom, if ever, consulted before speed limit signs are posted.

Charged with emotional controversy, speed limits attract more attention than any other traffic regulation. Much of this web site is devoted to clarifying the issues surrounding unsuccessful government efforts to control vehicle speed. It also presents engineering standards for setting fair, enforceable speed limits.

The next page examines the relationship between vehicle speed and safety in normal traffic flows.

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