The National Safety Commission Alerts
Safety is No Accident
Tuesday, September 01, 2009
Safe Roads and the Peltzman Effect
A study was released recently that got a lot of media attention along with some critical reviews. According to the study's authors, bad road conditions contributed to 52.7% of fatal collisions in the US. This report is a rare case faulting road construction as a factor. Most studies since 1979 have placed the blame for traffic collisions squarely on the driver either through driver error or inattention.
Many of the nation's highways are doubtless in bad shape and the state of bridges and overpasses is downright scary. There is no doubt that we need more and better roads to relieve the traffic burden; especially in large cities. However widening roads, adding more signs and clearer lane markers may not be the best answer. There have been some articles claiming that widening roads and painting clearer markings will lead to the "Peltzman Effect".
Sam Peltzman, a professor of Economics at the University of Chicago theorized that people tend to respond to safety regulations or safety technology by engaging in more dangerous behavior. He felt that people adjust their behavior to a regulation in ways that counteract the intended effect of the regulation. One study that found the Peltzman Effect to be true looked at increased safety technology in NASCAR race cars. This study found that safer cars and improved restraint devices have led to riskier behavior on the part of the race car drivers and an increase in collisions on the speedway.
The Insurance Institute for Highway Safety (IIHS), in looking at new technology to make cars safer, warned that systems designed to keep a car from automatically straying from the lane or from coming too close to a vehicle ahead are great in theory but they feel it will give drivers a false sense of security leading them to take their eyes off the road more often or allowing them to become more distracted. One wag went so far as to jokingly suggest, if you take the Peltzman Effect to its extreme, cars should be made of cardboard and have a large pointed spike in the center of the steering wheel pointed at the driver's chest. That would force drivers to drive more safely.
The intended effect of building wider, clearer roads is to improve the flow of traffic and to cut down on injuries and deaths due to collisions. The Peltzman Effect however says that, as roads are improved, drivers feel they can take greater risks and the average speed on the roadway increases. As a result, the intended effect of making the road safer is offset by riskier driving behavior and the rate of collisions is basically unchanged.
As a reaction to this, traffic engineers in cities around the world have moved to a European innovation known as "Traffic Calming". Traffic calming involves the use of restricted lanes, speed bumps, barriers, and warning signs painted directly onto the road surface in an attempt to slow or calm the traffic down. Probably the best and most visible examples of traffic calming procedures are the traffic circles that are replacing traditional four-way intersections. Traffic circles allow traffic to move through an intersection without the use of traffic lights. While the traffic is forced to slow down when entering the traffic circle, there are no long waits for traffic lights and traffic moves more smoothly.
Traffic calming has been implemented in towns and cities throughout the US from West Palm Beach Florida to Seattle Washington but the measures are usually very expensive to implement and maintain. Traffic calming is most often seen on urban streets with lower speeds. Studies conducted to gauge their effect on highways with higher speeds have had mixed or limited results.
Hans Monderman, a Dutch traffic engineer looked at some of the traffic calming procedures and felt they were ineffective. Monderman rejected the notion that wider roads and more warning signs created a safer environment. He was hired to look at a street in the Dutch village of Oudehaske, where speeding drivers had struck and killed two children. Instead of employing the typical traffic calming devices, Monderman removed the curbs, took out the signs, and used paving bricks that had the effect of making the road seem narrower. The effect was to create enough uncertainty in the minds of drivers that traffic immediately slowed down and the average speed was dramatically reduced. Without signs or lane markings, the effect changed driving behavior making drivers more accommodating and cooperative.
In another town he replaced a collision prone, traffic light controlled four-way intersection with what he referred to as a "traffic square," with no signs or signals. The result was a striking reduction in the collision rate and more cooperation between drivers, pedestrians, and cyclists. He often demonstrated the effectiveness of this new intersection by safely walking backwards down the street with his eyes closed.
Drivers on the road today may want to keep the Peltzman Effect in mind. Safer cars and wider roads don't necessarily make the driving environment safer and don't relieve the driver of the responsibility to maintain a safe speed and to pay attention to the road ahead.
National Safety Commission Alerts work to increase awareness of important safety issues, particularly those that deal with highway and traffic safety information. Our mission is to make consumers more vigilant and understand that "safety is no accident," through education, including online traffic school, driver education and outreach programs.
Many of the nation's highways are doubtless in bad shape and the state of bridges and overpasses is downright scary. There is no doubt that we need more and better roads to relieve the traffic burden; especially in large cities. However widening roads, adding more signs and clearer lane markers may not be the best answer. There have been some articles claiming that widening roads and painting clearer markings will lead to the "Peltzman Effect".
Sam Peltzman, a professor of Economics at the University of Chicago theorized that people tend to respond to safety regulations or safety technology by engaging in more dangerous behavior. He felt that people adjust their behavior to a regulation in ways that counteract the intended effect of the regulation. One study that found the Peltzman Effect to be true looked at increased safety technology in NASCAR race cars. This study found that safer cars and improved restraint devices have led to riskier behavior on the part of the race car drivers and an increase in collisions on the speedway.
The Insurance Institute for Highway Safety (IIHS), in looking at new technology to make cars safer, warned that systems designed to keep a car from automatically straying from the lane or from coming too close to a vehicle ahead are great in theory but they feel it will give drivers a false sense of security leading them to take their eyes off the road more often or allowing them to become more distracted. One wag went so far as to jokingly suggest, if you take the Peltzman Effect to its extreme, cars should be made of cardboard and have a large pointed spike in the center of the steering wheel pointed at the driver's chest. That would force drivers to drive more safely.
The intended effect of building wider, clearer roads is to improve the flow of traffic and to cut down on injuries and deaths due to collisions. The Peltzman Effect however says that, as roads are improved, drivers feel they can take greater risks and the average speed on the roadway increases. As a result, the intended effect of making the road safer is offset by riskier driving behavior and the rate of collisions is basically unchanged.
Traffic calming has been implemented in towns and cities throughout the US from West Palm Beach Florida to Seattle Washington but the measures are usually very expensive to implement and maintain. Traffic calming is most often seen on urban streets with lower speeds. Studies conducted to gauge their effect on highways with higher speeds have had mixed or limited results.
Hans Monderman, a Dutch traffic engineer looked at some of the traffic calming procedures and felt they were ineffective. Monderman rejected the notion that wider roads and more warning signs created a safer environment. He was hired to look at a street in the Dutch village of Oudehaske, where speeding drivers had struck and killed two children. Instead of employing the typical traffic calming devices, Monderman removed the curbs, took out the signs, and used paving bricks that had the effect of making the road seem narrower. The effect was to create enough uncertainty in the minds of drivers that traffic immediately slowed down and the average speed was dramatically reduced. Without signs or lane markings, the effect changed driving behavior making drivers more accommodating and cooperative.
In another town he replaced a collision prone, traffic light controlled four-way intersection with what he referred to as a "traffic square," with no signs or signals. The result was a striking reduction in the collision rate and more cooperation between drivers, pedestrians, and cyclists. He often demonstrated the effectiveness of this new intersection by safely walking backwards down the street with his eyes closed.
Drivers on the road today may want to keep the Peltzman Effect in mind. Safer cars and wider roads don't necessarily make the driving environment safer and don't relieve the driver of the responsibility to maintain a safe speed and to pay attention to the road ahead.
National Safety Commission Alerts work to increase awareness of important safety issues, particularly those that deal with highway and traffic safety information. Our mission is to make consumers more vigilant and understand that "safety is no accident," through education, including online traffic school, driver education and outreach programs.
Labels: Highway Fatality Rate, Highway Safety, Peltzman Effect
Wednesday, August 26, 2009
Drivers Don't See Speeding As A Safety Issue
A study conducted by Purdue University has found that most drivers feel it is safe to exceed the posted speed limit by 5, 10, or 20 mph. That is probably no surprise to anyone who regularly drives on America's roads. In spite of these driver attitudes, the studies continue show that speed kills.
According to an article in "Science Daily", the Purdue survey of drivers found that "21 percent thought it was safe to drive up to 5 mph over the speed limit, 43 percent thought it was safe to drive up to 10 mph over and 36 percent thought it was safe to drive up to 20 mph over the speed limit.According to the researchers, the attitude toward speeding may have something to do with the perception that speed limits are changed for political rather than safety reasons: The repeal of the federal maximum speed limit is most often cited as an example of changing speed limits for political reasons.
The researchers pointed out the need for stricter enforcement of speed limits. They felt that, where speed enforcement is perceived as lax, the statistics show that a driver is 27% more likely to feel that he or she can get away with driving up to 20 mph over the posted speed limit.
Another unrelated study from Australia showed that a driver, whose friends and family approve of his or her speeding, is more likely to drive over the speed limit. When driving, peer pressure apparently works no matter what the age. Where these drivers go wrong is in the assumption that their safety and physical well being aren't affected by increased speeds.
Numerous studies have shown that higher speeds increase the death and injury rates on the highways. When the federal maximum speed limit was reduced to 55 mph in 1974 as a result of the oil crisis, the fatality rate fell by 17 percent within the first year after enactment of the law. In the ten years after the 1995 repeal of the federal maximum speed limit, the figures showed that there were approximately 12,500 more deaths that could be attributed to the increased speeds.
Data from the state of Arizona shows that the state's highway fatality rate fell by 18 percent in the year following installation of speed cameras on major highways. A 2007 National highway and Transportation Safety Administration review of several studies showed that, where speed cameras were used to regulate speed, there were crash reductions of 20 to 25 percent for fixed speed cameras and 21 to 51 percent for mobile speed camera programs.
Several factors come into play when speed is involved. The first is driver distractions. A study published last year by Virginia Tech showed that more than 80 percent of crashes involved some sort of driver distraction within 3 seconds of the crash. The second factor is a driver's reaction time and that ties into the first. If a driver is paying attention to the road ahead, it can take up to 1.5 seconds before the driver perceives an emergency, decides what to do, and then acts on the decision; slamming on the brakes for example. In those 1.5 seconds, a vehicle going 40 mph will cover a distance of more than 88 feet; that is before the car actually begins to slow. At 40 mph, in ideal conditions, it can take almost 170 feet before your car comes to a complete stop. If a driver is distracted, you can add more time and distance to the reaction time and total braking distance.
The third factor is one that few drivers ever take into account; the physics of a car crash. Using a crash force calculator created by the physics department at Georgia State University, figures for the weight of a vehicle along with its speed can be plugged in to show the overall crash forces that the vehicle will experience. For example, a 3,000 pound car traveling at 30 mph will experience a crash force of 45.16 tons. Going from 30 to 40 mph is only a 33 percent increase in speed but it represents a 77 percent increase in crash forces.28 tons of crash force.
It would seem to make sense that a 60 mph crash would be twice as bad as a 30 mph crash but the crash forces are much greater than that. A speed of 60 mph over 30 mph represents a 100 percent increase in speed but it will increase the crash forces by 300 percent.
30 mph crash = 45.16 tons of force
60 mph crash = 180.64 tons of force
Higher speeds increase the distance traveled and decrease the time you have to react to an emergency situation. Higher speeds also increase crash forces exponentially.
According to an article in "Science Daily", the Purdue survey of drivers found that "21 percent thought it was safe to drive up to 5 mph over the speed limit, 43 percent thought it was safe to drive up to 10 mph over and 36 percent thought it was safe to drive up to 20 mph over the speed limit.According to the researchers, the attitude toward speeding may have something to do with the perception that speed limits are changed for political rather than safety reasons: The repeal of the federal maximum speed limit is most often cited as an example of changing speed limits for political reasons.
The researchers pointed out the need for stricter enforcement of speed limits. They felt that, where speed enforcement is perceived as lax, the statistics show that a driver is 27% more likely to feel that he or she can get away with driving up to 20 mph over the posted speed limit.
Another unrelated study from Australia showed that a driver, whose friends and family approve of his or her speeding, is more likely to drive over the speed limit. When driving, peer pressure apparently works no matter what the age. Where these drivers go wrong is in the assumption that their safety and physical well being aren't affected by increased speeds.
Numerous studies have shown that higher speeds increase the death and injury rates on the highways. When the federal maximum speed limit was reduced to 55 mph in 1974 as a result of the oil crisis, the fatality rate fell by 17 percent within the first year after enactment of the law. In the ten years after the 1995 repeal of the federal maximum speed limit, the figures showed that there were approximately 12,500 more deaths that could be attributed to the increased speeds.
Data from the state of Arizona shows that the state's highway fatality rate fell by 18 percent in the year following installation of speed cameras on major highways. A 2007 National highway and Transportation Safety Administration review of several studies showed that, where speed cameras were used to regulate speed, there were crash reductions of 20 to 25 percent for fixed speed cameras and 21 to 51 percent for mobile speed camera programs.
Several factors come into play when speed is involved. The first is driver distractions. A study published last year by Virginia Tech showed that more than 80 percent of crashes involved some sort of driver distraction within 3 seconds of the crash. The second factor is a driver's reaction time and that ties into the first. If a driver is paying attention to the road ahead, it can take up to 1.5 seconds before the driver perceives an emergency, decides what to do, and then acts on the decision; slamming on the brakes for example. In those 1.5 seconds, a vehicle going 40 mph will cover a distance of more than 88 feet; that is before the car actually begins to slow. At 40 mph, in ideal conditions, it can take almost 170 feet before your car comes to a complete stop. If a driver is distracted, you can add more time and distance to the reaction time and total braking distance.
The third factor is one that few drivers ever take into account; the physics of a car crash. Using a crash force calculator created by the physics department at Georgia State University, figures for the weight of a vehicle along with its speed can be plugged in to show the overall crash forces that the vehicle will experience. For example, a 3,000 pound car traveling at 30 mph will experience a crash force of 45.16 tons. Going from 30 to 40 mph is only a 33 percent increase in speed but it represents a 77 percent increase in crash forces.28 tons of crash force.
It would seem to make sense that a 60 mph crash would be twice as bad as a 30 mph crash but the crash forces are much greater than that. A speed of 60 mph over 30 mph represents a 100 percent increase in speed but it will increase the crash forces by 300 percent.
30 mph crash = 45.16 tons of force
60 mph crash = 180.64 tons of force
Higher speeds increase the distance traveled and decrease the time you have to react to an emergency situation. Higher speeds also increase crash forces exponentially.
Labels: Highway Fatality Rate, Speed Limit, speeding
