Engineering Myths and Realities?
What Is Traffic Engineering
Myths Of Traffic Engineering
Why Can't We Have 4-Way STOP Signs
What's The Harm Of Installing Unwarranted Devices
What Can Citizens Do To Help Reduce Accidents
Why Can't We Have SPEED BUMPS On Our Street
Why Can't We Have A Reduced Speed Limit
How Are Speed Limits Established
Won't STOP Signs Slow Speed On Our Street
Myths Of Traffic Engineering
Why Can't We Have 4-Way STOP Signs
What's The Harm Of Installing Unwarranted Devices
What Can Citizens Do To Help Reduce Accidents
Why Can't We Have SPEED BUMPS On Our Street
Why Can't We Have A Reduced Speed Limit
How Are Speed Limits Established
Won't STOP Signs Slow Speed On Our Street
One of the greatest obstacles a professional traffic engineer faces in applying sound principles of traffic control is that everyone who has a drivers license is convinced that they are traffic experts. Consequently the traffic engineer is given not only the diagnosis of a traffic problem, but a remedy as well. For example, someone calls and says. "I almost got hit turning left at Buckeye Road and 51st Avenue - what we need there is a left turn arrow - how long will it take to put it in?" In a sense this would be like calling your doctor and saying. "Doc, I've got a pain in my stomach - what I need is my appendix removed - how soon can you do the operation?"
At this point let me hasten to say that most traffic engineers encourage information, input, and suggestions from the public. This is one of the ways that they become aware of existing or potential traffic operational problems. Engineers must be receptive to input from the public and attempt to overcome the built-in handicaps by trying to communicate in a common understandable language.
What I would like to do is to review a couple of the myths and realities pertaining to traffic engineering and traffic controls.
Myth Number 1: The public knows and cares about traffic engineering principles, objectives, analyses, alternatives, and methods.
Reality: The familiar expression "Don't confuse me with the facts, my mind is made up!" unfortunately has widespread acceptance. The public is handicapped by a short attention span and an aversion to facts, logic, or viewpoints that are contrary to its personal opinions and emotions.
Myth Number 2: Traffic control devices (signs, signals, and markings) provide an effective solution to almost any traffic problem.
Reality: There is widespread public unwillingness to accept abundant evidence of limited effectiveness of various devices in solving basic design or construction deficiencies. The political need to "do something that might help, doesn't cost much, and can't hurt" is overpowering and further encourages the public demand. The fallacy lies in thinking that a safer condition prevails when actually this may not be the case.
Let's take a look at a few of the common traffic controls in view of the myths and the realities.
Interestingly, however, there is strong evidence that these very facts prompt many pedestrians to feel overly secure when using a marked crosswalk - to the degree that they aggressively place themselves in a hazardous position with respect to vehicles in the mistaken belief that the motorist can and will stop in all cases, even when it may be impossible to do so. It is not unusual, also, for this type of aggressive pedestrian behavior to cause rear-end collisions.
By contrast, a pedestrian using an unmarked crosswalk generally feels less secure, less certain that the motorist will stop - and exercises more caution in waiting for safe gaps in traffic before crossing. The end result is fewer accidents at unmarked crosswalks.
One of the commonly accepted functions of the marked crosswalk is that it serves as a warning device to the motorists. Yet, studies show that the motorists' views of a crosswalk are greatly reduced when they are at the safe stopping sight distance - where they should be able to perceive and react to a pedestrian in a crosswalk due to the effects of foreshortening and distance diminishment. Their view of the crosswalk is further affected by road alignment, irregularities in the pavement, and other variables like weather, dirty windshields, glare, and adverse lighting conditions.
Meanwhile, pedestrians views of the same crosswalk are quite impressive and they are prone to assume that since they can see the crosswalk so well, certainly motorist can see it just as clearly. This resulting overconfidence is seen as another factor in the disproportionate share of accidents in marked crosswalks.
Does this mean marked crosswalks should not be installed? Not necessarily. The marked crosswalk is a useful device for channelizing pedestrians and helping pedestrians find their way across complex and confusing intersections. The decision to install or not install a marked crosswalk should not be taken lightly. Rational warrants have been adopted by many governmental jurisdictions for their installation.
It is important that the general public recognize what marked crosswalks can and cannot do. It is also important that public officials not install them unless the anticipated benefits outweigh the risks.
Signals offer maximum control at intersections they relay messages of both what to do and what not to do. The primary function of any traffic signal is to assign right-of-way to conflicting movements of traffic at an intersection, and it does this by permitting conflicting streams of traffic to share the same intersection by means of time separation.
By alternately assigning right-of-way to various traffic movements, signals provide for the orderly movement of conflicting flows. They may interrupt extremely heavy flows to permit the crossing of minor movements that could not otherwise move safely through the intersection.
When properly timed, the traffic signal increases the traffic handling capacity of an intersection, and when installed under conditions that justify its use, it is a valuable device for improving the safety and efficiency of both pedestrian and vehicular traffic. In particular, signals may reduce certain types of accidents, most notably the angle (broadside) collision.
While many people realize that traffic signals can reduce the number of angle collisions, few realize that signals also cause a significant increase in rear-end collisions.
Normally traffic engineers are willing to trade off an increase in rear-end collisions for a decrease in more severe angle accidents; however, when there is no angle accident problem at an intersection and a signal is not recommended for traffic control, there is nothing to trade off and the installation of traffic signals can actually cause a deterioration in the overall safety at the intersection. This situation sometimes prompts the remark, "You mean you won't do anything until somebody gets killed!" What is not fully understood is that traffic signals are not a "cure-all" and that the primary goal of the traffic engineer is to attain the safest and most efficient traffic flow feasible.
In addition to an increase in accident frequency, unjustified traffic signals can also cause excessive delay, disobedience of signals, and diversion of traffic to residential streets.
Traffic signals are more costly than is commonly realized, even though they represent a sound public investment when justified. A modern signal can cost taxpayers between $50,000 and $100,000 to install, depending on the complexity of the intersection and the characteristics of the traffic using it. On top of this, there is a perpetual cost that is almost never considered-- the cost of electrical power consumed in operating a signalized intersection 24 hours a day. This now averages about $1400 a year.
Before and after studies consistently demonstrate that there are no significant changes in traffic speeds following the posting of new or revised speed limits. Furthermore, no published research findings have established any direct relationship between posted speed and accident frequency, although short-term reductions have resulted from saturation enforcement efforts directed at speed and other traffic law violations. Police agencies necessarily rely on reasonable and well recognized speed laws to control the unreasonable violator whose behavior is clearly out of line with the normal flow of traffic.
Contrary to popular belief, speed in itself is not a major cause of accidents. In fact, there is a consensus of professional opinions that many speed related accidents result from both excessively low and high speeds.
Then why have speed limits?
Realistic speed limits, that is, speed limits that reflect the normal actions of the reasonable driver, are useful for several reasons:
They invite public compliance by conforming to the behavior of the majority.
They give a clear reminder of reasonable and prudent speeds to non-conforming violators.
They offer an effective enforcement tool to the police.
They tend to minimize the public antagonism toward police enforcement that results from unreasonable regulations.
On the other hand, unrealistic speed limits can be detrimental:
They do not invite voluntary compliance, since they do not reflect the behavior of the majority.
They make the behavior of the majority unlawful.
They create public antagonism toward the police, since the police are enforcing a known "speed trap".
They create a bad image for a community in the eyes of tourists.
One of the more common locations where a flasher can be used effectively is at a signalized intersection located just beyond a vertical or horizontal curve, when the intersection is hidden from the view of approaching motorists.
For any flasher to be effective, it must command the respect of the motoring public. In other words, immediately after seeing a flasher, the driver must consistently see an unusual condition that is being singled out for attention. Furthermore, the condition that motorist see must be viewed as serious enough to justify their having been alerted.
When flashers are used improperly and installed at locations where they are not warranted, they soon loose much of their effectiveness. They simply cease to command respect of the drivers. What happens is that after continually being alerted to a condition which is seldom, if ever, appears to be truly unusual, drivers actually stop "seeing" the flasher. When this happens, flashers that are truly needed may also be disregarded by drivers who have become conditioned to believe that flashers are just "window dressing". Because of this normal human reaction, even one improper usage greatly reduces the effectiveness of essential flashers.
Quite often, community requests for flashers are emotional responses to symptoms, rather than attempts to resolve underlying problems. To put this into perspective, let's use an appropriate analogy: the case of measles. Obviously, to cure a patient who has measles, the disease itself (measles must be treated--not the symptom(rash). In traffic control, it is not uncommon for public responses to be directed at treating symptoms. For example, in cases where concerned parents are requesting flashers on pedestrian warning signs, a traffic investigation all too frequently reveals that:
There is no "safe route to school" plan in the community.
There is no pedestrian safety program in the schools.
Very young children are allowed to wander to school by whatever route their youthful minds prefer.
Parents are willing to abdicate their responsibilities by placing the entire burden for pedestrian safety on a traffic control device.
Local law enforcement officials turn a blind eye to youthful pedestrian traffic violations.
Where traffic laws are enforced by conscientious law enforcement officials, outraged parents explain away the irresponsible behavior of their children by claiming that the fault lies in inadequate traffic control devices, not in their children.
Flashers that are installed when these conditions exist result in the following:
The flasher soon becomes part of the normal driving environment and is ignored.
Parents continue to ignore their responsibilities to their children.
The community continues to avoid treating the real problem.
Other flashers, which are justified, are frequently disregarded by motorists conditioned to believe that flashers can be safely disregarded.
In summary, when flashers are properly located, they serve a useful function. When they are used improperly and installed at locations where they are not warranted, they soon lose much, if not all of their effectiveness. More seriously, improper usage greatly reduces the effectiveness of other flashers installed in areas where there is a real need.
Above all, it is essential to prove that there is a problem which can be solved through the installation of a flasher before actually employing one. Too often, flashers are installed when someone assumes there is, or is going to be, a problem. It is important the flasher installation be minimized to maintain a high degree of respect for the flasher installations that are truly needed.
In conclusion, many people still wonder why an "obvious" traffic problem is so difficult that someone called a traffic engineer should be needed to develop a solution. Hopefully, the preceding discussion has been in a common understandable language that will help overcome the built in handicap inherent in communications between laymen and professionals.
SOURCE: Public Works Magazine for January 1990
At this point let me hasten to say that most traffic engineers encourage information, input, and suggestions from the public. This is one of the ways that they become aware of existing or potential traffic operational problems. Engineers must be receptive to input from the public and attempt to overcome the built-in handicaps by trying to communicate in a common understandable language.
What I would like to do is to review a couple of the myths and realities pertaining to traffic engineering and traffic controls.
Myth Number 1: The public knows and cares about traffic engineering principles, objectives, analyses, alternatives, and methods.
Reality: The familiar expression "Don't confuse me with the facts, my mind is made up!" unfortunately has widespread acceptance. The public is handicapped by a short attention span and an aversion to facts, logic, or viewpoints that are contrary to its personal opinions and emotions.
Myth Number 2: Traffic control devices (signs, signals, and markings) provide an effective solution to almost any traffic problem.
Reality: There is widespread public unwillingness to accept abundant evidence of limited effectiveness of various devices in solving basic design or construction deficiencies. The political need to "do something that might help, doesn't cost much, and can't hurt" is overpowering and further encourages the public demand. The fallacy lies in thinking that a safer condition prevails when actually this may not be the case.
Let's take a look at a few of the common traffic controls in view of the myths and the realities.
Pedestrian Crosswalks
How safe are they? How secure are you in a crosswalk? Marked crosswalks are widely classified as "safety devices" and most jurisdictions give the pedestrian the right-of-way when within them.Interestingly, however, there is strong evidence that these very facts prompt many pedestrians to feel overly secure when using a marked crosswalk - to the degree that they aggressively place themselves in a hazardous position with respect to vehicles in the mistaken belief that the motorist can and will stop in all cases, even when it may be impossible to do so. It is not unusual, also, for this type of aggressive pedestrian behavior to cause rear-end collisions.
By contrast, a pedestrian using an unmarked crosswalk generally feels less secure, less certain that the motorist will stop - and exercises more caution in waiting for safe gaps in traffic before crossing. The end result is fewer accidents at unmarked crosswalks.
One of the commonly accepted functions of the marked crosswalk is that it serves as a warning device to the motorists. Yet, studies show that the motorists' views of a crosswalk are greatly reduced when they are at the safe stopping sight distance - where they should be able to perceive and react to a pedestrian in a crosswalk due to the effects of foreshortening and distance diminishment. Their view of the crosswalk is further affected by road alignment, irregularities in the pavement, and other variables like weather, dirty windshields, glare, and adverse lighting conditions.
Meanwhile, pedestrians views of the same crosswalk are quite impressive and they are prone to assume that since they can see the crosswalk so well, certainly motorist can see it just as clearly. This resulting overconfidence is seen as another factor in the disproportionate share of accidents in marked crosswalks.
Does this mean marked crosswalks should not be installed? Not necessarily. The marked crosswalk is a useful device for channelizing pedestrians and helping pedestrians find their way across complex and confusing intersections. The decision to install or not install a marked crosswalk should not be taken lightly. Rational warrants have been adopted by many governmental jurisdictions for their installation.
It is important that the general public recognize what marked crosswalks can and cannot do. It is also important that public officials not install them unless the anticipated benefits outweigh the risks.
Traffic Signals
Are traffic signals the answer to intersection traffic problems? Let's look at the advantages and disadvantages.Signals offer maximum control at intersections they relay messages of both what to do and what not to do. The primary function of any traffic signal is to assign right-of-way to conflicting movements of traffic at an intersection, and it does this by permitting conflicting streams of traffic to share the same intersection by means of time separation.
By alternately assigning right-of-way to various traffic movements, signals provide for the orderly movement of conflicting flows. They may interrupt extremely heavy flows to permit the crossing of minor movements that could not otherwise move safely through the intersection.
When properly timed, the traffic signal increases the traffic handling capacity of an intersection, and when installed under conditions that justify its use, it is a valuable device for improving the safety and efficiency of both pedestrian and vehicular traffic. In particular, signals may reduce certain types of accidents, most notably the angle (broadside) collision.
While many people realize that traffic signals can reduce the number of angle collisions, few realize that signals also cause a significant increase in rear-end collisions.
Normally traffic engineers are willing to trade off an increase in rear-end collisions for a decrease in more severe angle accidents; however, when there is no angle accident problem at an intersection and a signal is not recommended for traffic control, there is nothing to trade off and the installation of traffic signals can actually cause a deterioration in the overall safety at the intersection. This situation sometimes prompts the remark, "You mean you won't do anything until somebody gets killed!" What is not fully understood is that traffic signals are not a "cure-all" and that the primary goal of the traffic engineer is to attain the safest and most efficient traffic flow feasible.
In addition to an increase in accident frequency, unjustified traffic signals can also cause excessive delay, disobedience of signals, and diversion of traffic to residential streets.
Traffic signals are more costly than is commonly realized, even though they represent a sound public investment when justified. A modern signal can cost taxpayers between $50,000 and $100,000 to install, depending on the complexity of the intersection and the characteristics of the traffic using it. On top of this, there is a perpetual cost that is almost never considered-- the cost of electrical power consumed in operating a signalized intersection 24 hours a day. This now averages about $1400 a year.
Speed Limits
One of the most prevalent myths around is that motorists will adjust their speed in response to the numbers posted on speed limit signs regardless of roadway and traffic conditions.Before and after studies consistently demonstrate that there are no significant changes in traffic speeds following the posting of new or revised speed limits. Furthermore, no published research findings have established any direct relationship between posted speed and accident frequency, although short-term reductions have resulted from saturation enforcement efforts directed at speed and other traffic law violations. Police agencies necessarily rely on reasonable and well recognized speed laws to control the unreasonable violator whose behavior is clearly out of line with the normal flow of traffic.
Contrary to popular belief, speed in itself is not a major cause of accidents. In fact, there is a consensus of professional opinions that many speed related accidents result from both excessively low and high speeds.
Then why have speed limits?
Realistic speed limits, that is, speed limits that reflect the normal actions of the reasonable driver, are useful for several reasons:
They invite public compliance by conforming to the behavior of the majority.
They give a clear reminder of reasonable and prudent speeds to non-conforming violators.
They offer an effective enforcement tool to the police.
They tend to minimize the public antagonism toward police enforcement that results from unreasonable regulations.
On the other hand, unrealistic speed limits can be detrimental:
They do not invite voluntary compliance, since they do not reflect the behavior of the majority.
They make the behavior of the majority unlawful.
They create public antagonism toward the police, since the police are enforcing a known "speed trap".
They create a bad image for a community in the eyes of tourists.
Flashing Beacons
Do they really cause motorists to reduce their speeds? Flashing beacons (commonly called flashers or flashing lights) are frequently requested by communities in the belief that they will reduce vehicle speeds. Unfortunately, this is not necessarily the case. A flasher is generally installed at an intersection or in conjunction with a warning sign in advance of the area requiring greater than normal care by the average driver. Flashing beacons serve a useful purpose where the flashing yellow is used to alert drivers to unusual conditions that are not readily apparent, such as obstructions in the roadway, uncommon roadway conditions, narrow bridges, or unusual conditions hidden from the motorist's view.One of the more common locations where a flasher can be used effectively is at a signalized intersection located just beyond a vertical or horizontal curve, when the intersection is hidden from the view of approaching motorists.
For any flasher to be effective, it must command the respect of the motoring public. In other words, immediately after seeing a flasher, the driver must consistently see an unusual condition that is being singled out for attention. Furthermore, the condition that motorist see must be viewed as serious enough to justify their having been alerted.
When flashers are used improperly and installed at locations where they are not warranted, they soon loose much of their effectiveness. They simply cease to command respect of the drivers. What happens is that after continually being alerted to a condition which is seldom, if ever, appears to be truly unusual, drivers actually stop "seeing" the flasher. When this happens, flashers that are truly needed may also be disregarded by drivers who have become conditioned to believe that flashers are just "window dressing". Because of this normal human reaction, even one improper usage greatly reduces the effectiveness of essential flashers.
Quite often, community requests for flashers are emotional responses to symptoms, rather than attempts to resolve underlying problems. To put this into perspective, let's use an appropriate analogy: the case of measles. Obviously, to cure a patient who has measles, the disease itself (measles must be treated--not the symptom(rash). In traffic control, it is not uncommon for public responses to be directed at treating symptoms. For example, in cases where concerned parents are requesting flashers on pedestrian warning signs, a traffic investigation all too frequently reveals that:
There is no "safe route to school" plan in the community.
There is no pedestrian safety program in the schools.
Very young children are allowed to wander to school by whatever route their youthful minds prefer.
Parents are willing to abdicate their responsibilities by placing the entire burden for pedestrian safety on a traffic control device.
Local law enforcement officials turn a blind eye to youthful pedestrian traffic violations.
Where traffic laws are enforced by conscientious law enforcement officials, outraged parents explain away the irresponsible behavior of their children by claiming that the fault lies in inadequate traffic control devices, not in their children.
Flashers that are installed when these conditions exist result in the following:
The flasher soon becomes part of the normal driving environment and is ignored.
Parents continue to ignore their responsibilities to their children.
The community continues to avoid treating the real problem.
Other flashers, which are justified, are frequently disregarded by motorists conditioned to believe that flashers can be safely disregarded.
In summary, when flashers are properly located, they serve a useful function. When they are used improperly and installed at locations where they are not warranted, they soon lose much, if not all of their effectiveness. More seriously, improper usage greatly reduces the effectiveness of other flashers installed in areas where there is a real need.
Above all, it is essential to prove that there is a problem which can be solved through the installation of a flasher before actually employing one. Too often, flashers are installed when someone assumes there is, or is going to be, a problem. It is important the flasher installation be minimized to maintain a high degree of respect for the flasher installations that are truly needed.
In conclusion, many people still wonder why an "obvious" traffic problem is so difficult that someone called a traffic engineer should be needed to develop a solution. Hopefully, the preceding discussion has been in a common understandable language that will help overcome the built in handicap inherent in communications between laymen and professionals.
SOURCE: Public Works Magazine for January 1990
