Defending Automobile Manufacturers in Design Defect Cases

Counsel defending manufacturers who are alleged to have designed defective vehicles that have caused serious traffic accidents often have an uphill battle in convincing jurors that the design of their client's vehicle was not wholly responsible for the accident and resultant injuries and damages. If the defect is not at issue, the defense attorney may seek to prove that the driver of the vehicle was at least partially at fault ' and that often requires extensive analysis of various factors.

The good news is that jury pools are populated with persons who have first-hand knowledge of reckless and aggressive drivers. They are also well aware of the frequency of accidents and their toll in lives and injuries, i.e., 6,420,000 crashes and 42,636 deaths each year (2005), a rate of 115 deaths per day. In addition, as courts and jurors are called on to examine the various facts presented in these cases and, in order to apportion causality, they are most often provided with reports and testimony from accident reconstructionists, employed by law enforcement or private consulting firms. The reconstructionists compute the coefficient of friction of the road surface, measure skid marks in evidence on the road's surface, analyze the vehicles' damage to determine impact forces, make estimates about the speed of the vehicles, and generally provide a description of the physical forces at work in various accident scenarios. Such computations, however, only tell part of the accident story. An equally important dimension involves the human factors issues involved and, in particular, driver reaction times. This is where the plaintiff's counsel will present the other side of the story.

There are, of course, other factors that must be weighed in providing a complete analysis of the accident incident. These factors involve the drivers and their physiological and psychological attributes. This is an area where human factors analysis can potentially be of value to defense counsel engaged in accident analysis.

Physical Deficits

Obviously, certain of the drivers' basic physical conditions must be accounted for, since these factors could influence the defendant's reaction times. Some examples include:

• Any vision deficits must be considered, e.g., the failure to wear appropriate prescription glasses if required, the presence of night blindness (nyctalopia), cataract obstructions, ocular disease, etc.;
• Any balance deficits involved, e.g., labrynthitis, Meniere's disease, vertigo, etc.;
• Chronic neurological deficits that would slow or hinder movement of key muscle groups;
• Pre-existing skeletal injuries that would affect limb movement and restrict operation of the vehicle in an emergency scenario; and
• Use of any substances, drugs and/or alcohol that might have impaired judgement and/or operational control.

Matters of Age and Gender

While it may not be politically correct to point out, many women have slightly longer reaction times than their male age peers, according to ergonomic research by J. Adam and others. In most instances these variations do not rise to the level where they are, per se, significant factors in accident causation. In some instances, however, gender differences, when combined with certain physical and/or psychological issues, may become worthy of study as causative factors in accident analysis.

Age is a somewhat different matter. Most research confirms a gradual increase in reaction times due to normal aging. Gerontologists such as John Botwinick, as early as 1966, made note of the fact that some older drivers are aware of their limitations and alter their driving practices to accommodate slower reaction times. In essence, the communication time between neurons lengthens with age. Recent research by neurologist George Bartzokis at UCLA suggests that declines in the motor control cortex start far earlier than first suspected ' as early as age 40. As we age, the thickness of myelin, the insulation around our nerve fibers, decreases, and this affects the conduction rate of the signals the brain sends to muscle groups. By the time many motorists reach 65, there can be a significant increase in their reaction times. However, it is important for counsel to point out that it would be improper to generalize because research also confirms a wide variability in reaction times between older drivers. Those persons who have stayed active, both physically and mentally, can have markedly better reaction times than the average of their age cohort.

Behavioral Issues

Once physical impediments are ruled out, the analysis must then turn to psychological and environmental issues that might have contributed, in some fashion, to sub-par driving performance. Obviously, one must consider driving behavior patterns, which may compress the reaction time available to drivers. For example, it may be useful to consider issues such as:

• Tailgating;
• Improper lane changing;
• Disposition to excessive speeds; and
• Failure to yield right of way.

Opposing counsel will point out that any of the above conditions can reduce the reaction time needed for the plaintiff to take evasive maneuvers and that such behavior itself can contribute to accident causation.

Distraction Effects

The single largest category of effects that lengthen reaction times is grouped under the umbrella term distractions ' a simple term that encompasses a universe of issues and sources. Nearly every juror will be able to recall distractions during his or her own driving experience. Exactly how much distraction contributes to vehicle accidents is a matter of some debate. However, it is safe to state that distraction is a major contributor. A government funded $4.2 million study, carried out by the Virginia Tech Transportation Institute, tracked 241 drivers for over 42,000 hours of driving, and found that 80% of accidents could be attributed to driver distraction. Other studies have suggested lower percentages. A much earlier study (1970) at Indiana University of pre-accident factors found driver inattention was a leading cause of accidents. Moreover, the American Automobile Association rates 20%-50% of all accidents as having originated in driver distraction.

In recent years, much of the distraction debate has focused on cell phones with an estimated 85% of cell phone users admitting that they use their phones while driving. Persons operating vehicles, while using any form of cell phone, are adjudged to be as cognitively distracted (impaired) as persons who exceed the blood alcohol limits in all of the 50 states. However, a whole variety of other “cockpit behaviors” feed the distraction total. Eating while driving, intense conversation with passengers, and attention to on-board GPS systems are all well-known distractors.

The point is that each of these activities, as a result of both the physical and cognitive demands they impose on the driver, can significantly add to his or her normal reaction time. Unfortunately from an accident analysis standpoint, it is often difficult to determine exactly what distractors, if any, were present just before the accident. Cell phone records can provide a clue to that factor, and food and drink in the vehicle provide their own clues, but pinpointing other distractors is much more difficult. In a number of cases, the impact of episodic memory loss, triggered by a cascade of endorphins released into the brain at the time of accident-related physical trauma, makes it difficult for the defendant to describe to the analyst exactly what he/she was doing or thinking about just prior to the accident.

Tracing Reaction Potentials

What all of these distractions have in common is that they can adversely affect, i.e., lengthen, driver reaction times. To understand reaction times, it useful for jurors first to understand some of the basic neurological facts associated with our reaction to stimuli ' visual stimuli in the case of vehicle drivers. As light photons, containing multiple images of the traffic scene about us, enter the human eye, they fall on the light'energy-sensitive rods and cones of the retina on the back wall of the eye. The eyes' optical systems focus the image, the “target,” on the fovea, an area of the macula with a dense concentration of cone-shaped light receptors. The nerve messages are funneled through the fovea in the center of the eye and then passed back through the optic chiasm to a switching station further back in the brain, in the thalmus, the lateral geniculate nucleus, and thence to the visual cortex in the brain's occipital lobe. Other portions of the brain, e.g., thalmus, etc., then have a neural conversation among themselves (an obvious oversimplification) and pass a command message to the frontal brain lobe's motor cortex and then down the spinal cord to the appropriate muscle groups that act on the brain's command, e.g., lift your right foot off the accelerator and press on the brake, steer right, etc. All of this takes time ' a surprisingly long time when you consider that the driver is hurtling forward at speeds that sometimes exceed more than 100 feet per second. This is an area of understanding that jurors may fail to appreciate. Moreover, if a driver's visual acuity is compromised by cataracts, macular degeneration, diabetic retinopathy, etc., we can expect reaction times to be adversely affected. In addition, intrinsic brain disorders such as multiple sclerosis, tumors and stroke-related vascular damage will also impede signal travel time to and from the visual cortex.

As might be expected, things get more complicated as we further examine this process. Obviously, if the driver is substance- impaired, it will be argued that reaction times stretch out. However, they also stretch out for drivers who are fatigued, and they increase for drivers who have recently experienced some life-altering event, e.g., death of spouse, loss of job, interpersonal conflict, serious illness, etc. They may even differ depending on what time and day of the week an accident may take place (a compilation by Human Benchmark suggests 4:00 p.m. on Tuesdays is the worst.)

Types of Reaction Times

When we come to estimate reaction times, it is first useful to divide reaction time into two simple categories, i.e., simple reactions and choice reactions. We often encounter simple reaction times in conditioned reflex responses, ones in which neural response patterns, i.e., pathways, are already established or ones that we are alerted to expect to use. For example, as we approach a traffic'light-controlled intersection, and observe a green light, we can expect a change in the light signal from green to yellow to red. We do not have to think about what to do. We “automatically” brake when the light turns red.

Measuring Reaction Times

While there is no nationally recognized standard for simple response times for drivers (and given the variation in drivers' neurological attributes, there probably should not be), one of the most frequently cited ranges is 1.4 to 1.5 seconds. (In laboratory tests, humans can often react within 0.7 seconds ' but not in driving conditions). This a measure of the time span necessary for the light stimulus to fall on the retina to the subsequent time needed to initiate muscular reaction (application of mechanical force). That, however, is not the end of the reaction time equation. There is also the matter of latency. Simply pressing the brake pedal does not instantly result in the vehicle's brakes' taking hold. The vehicle's own “nervous system” must be accounted for. Hydraulic fluid must be energized, brake rotors activated, etc. Vehicle system latency can add an additional 0.3 seconds to the time between when the road obstacle, condition, etc., is seen and brakes applied and when the brakes begin to slow the vehicle's tire rotations.

Choice Reaction Times

It should be noted, however, that the average 1.4 -1.5 second reaction time is premised on simple reaction responses, scenarios in which there is little or no event surprise and where there is little choice option i.e., where alternative crash avoidance situations need not be considered, where the brain does not have to engage in choice decisions. In many accident scenarios, drivers will be dealing with choice reaction time, and these choice decisions do, as expected, lengthen reaction time ' but by how much?

A typical situation involves a stopped vehicle in a travel lane. Should the driver focus solely on coming to a stop behind the vehicle or both brake and try to steer around the vehicle? The closing distance, the rate of closure, the presence, or absence, of oncoming traffic in the opposing lane, etc., are all issues that the driver must weigh ' in fractions of a second ' and each of these considerations slightly increases overall reaction time.

Some research has suggested that, as the brain weighs various alternatives, recovers from event surprise, etc., such choice situations may even require a doubling of simple reaction times. A conservative estimate may have such reaction times increasing by at least one third. Thus, a choice reaction time would exceed 2.0 seconds.

Effect of Expectation

Reaction times can be shortened by expectation of a particular stimulus. In effect, the brain is put on notice ' alerted ' that in the immediate future the driver will be likely to encounter the need for a braking response and/or steering evasion maneuver. Consider, for example, roadside signs that announce:

• Danger: Deer Crossing Ahead.
• Caution: Falling Rocks.
• Warning: Bridge Freezes Before Road Surface.
• School Zone: Slow Speed Ahead.
• Beware: High-Density Traffic Area.

Such signage can ' and does ' affect driver behavior. Drivers intuitively reduce speed, increase the range of their vision sweep and prepare themselves, in a reaction sense, to take collision avoidance maneuvers. Such cognitive preparation can reduce the choice intervals in reaction times and drive reaction times more towards simple reaction time parameters. Of course, the lack of warnings can have an opposite effect. A surprise event, a deer bounding from behind a roadside hedge, a child dashing out from between parked cars, and so forth, may have such an element of surprise that reaction times may double from simple reaction time standards. Thus, in evaluating reaction times associated with a particular accident scenario jurors must be educated to take into account the issue of expectation and its likely impact on compressing or expanding reaction time parameters.

Combining Speed and Reaction Times

One of the crucial analytic questions that needs to be answered is: If the design defect is not the (entire) cause of the accident, could the driver have prevented this accident? To answer that question, the focus must shift to the distance point when the driver most likely first observed the obstruction ahead of him/her and whether, at any reasonable and legal speed, could the driver have stopped in time to avoid a collision? To derive physical constants, reconstructionists can work their formulas to provide speed estimates in the area just before vehicle impacts. The reconstructionist begins by attempting to determine the coefficient of friction (COF) of the road surface on which the accident took place. On dry asphaltic road surfaces, with normal tire tread, we can expect a COF of 0.8. On a rainy surface the amount of friction available decreases (the road gets more slippery) and the COF may drop to 0.7 to 0.6. To determine the COF the reconstructionist typically employs one of three methods. An accelerometer/computer may be mounted on the windshield or floor of a test vehicle(often a police cruiser), a test run initiated with a skid stop and a direct digital readout provided calculating the road surface's COF . It is also possible to use a portable Drag Box with a portion of a rubber tire mounted on its underside. The Drag Box is towed at a constant speed over the road surface and the resistance measured by an on-board gauge.

The reconstructionist may also choose to use a test vehicle that skids to a stop from a known initial velocity and the speed determined by measuring the length of the skid and entering that value, along with the velocity, into the formula:

2

' = V /255 S

Once the vehicle speed is estimated in MPH, the reconstructionist can then multiply this value times 1.4666 to determine the number of feet per second that the vehicle was traveling. For example, if the vehicle was traveling at 83 miles per hour, it would traverse 121.7333 feet each second. In such a scenario, with a 2.0-second reaction time, the driver would travel 243.4666 feet before he/she even applied the brakes. To this value the reconstructionist must then add the length of the skid marks to obtain the total distance between when the obstruction was sighted and the point of impact. Even at moderate speeds, e.g., 45 MPH (66 feet per second) a 2.0 second reaction time means that the driver will travel 132 feet before his/her foot even touches the brake pedal. Add in vehicle latency time and skidding distance, and it may take up to 200 feet to come to a full stop.

Conclusion

In summary, jurors may understand that there is not a lot we can do to improve human reaction times significantly. However, consideration of the many factors involved may demonstrate that the design defect was not the cause of the accident and the resulting injuries and damage.

E. Patrick McGuire is president of Padric Associates, a behavioral science research firm in Clinton, NJ.

Counsel defending manufacturers who are alleged to have designed defective vehicles that have caused serious traffic accidents often have an uphill battle in convincing jurors that the design of their client's vehicle was not wholly responsible for the accident and resultant injuries and damages. If the defect is not at issue, the defense attorney may seek to prove that the driver of the vehicle was at least partially at fault ' and that often requires extensive analysis of various factors.

The good news is that jury pools are populated with persons who have first-hand knowledge of reckless and aggressive drivers. They are also well aware of the frequency of accidents and their toll in lives and injuries, i.e., 6,420,000 crashes and 42,636 deaths each year (2005), a rate of 115 deaths per day. In addition, as courts and jurors are called on to examine the various facts presented in these cases and, in order to apportion causality, they are most often provided with reports and testimony from accident reconstructionists, employed by law enforcement or private consulting firms. The reconstructionists compute the coefficient of friction of the road surface, measure skid marks in evidence on the road's surface, analyze the vehicles' damage to determine impact forces, make estimates about the speed of the vehicles, and generally provide a description of the physical forces at work in various accident scenarios. Such computations, however, only tell part of the accident story. An equally important dimension involves the human factors issues involved and, in particular, driver reaction times. This is where the plaintiff's counsel will present the other side of the story.

There are, of course, other factors that must be weighed in providing a complete analysis of the accident incident. These factors involve the drivers and their physiological and psychological attributes. This is an area where human factors analysis can potentially be of value to defense counsel engaged in accident analysis.

Physical Deficits

Obviously, certain of the drivers' basic physical conditions must be accounted for, since these factors could influence the defendant's reaction times. Some examples include:

• Any vision deficits must be considered, e.g., the failure to wear appropriate prescription glasses if required, the presence of night blindness (nyctalopia), cataract obstructions, ocular disease, etc.;
• Any balance deficits involved, e.g., labrynthitis, Meniere's disease, vertigo, etc.;
• Chronic neurological deficits that would slow or hinder movement of key muscle groups;
• Pre-existing skeletal injuries that would affect limb movement and restrict operation of the vehicle in an emergency scenario; and
• Use of any substances, drugs and/or alcohol that might have impaired judgement and/or operational control.

Matters of Age and Gender

While it may not be politically correct to point out, many women have slightly longer reaction times than their male age peers, according to ergonomic research by J. Adam and others. In most instances these variations do not rise to the level where they are, per se, significant factors in accident causation. In some instances, however, gender differences, when combined with certain physical and/or psychological issues, may become worthy of study as causative factors in accident analysis.

Age is a somewhat different matter. Most research confirms a gradual increase in reaction times due to normal aging. Gerontologists such as John Botwinick, as early as 1966, made note of the fact that some older drivers are aware of their limitations and alter their driving practices to accommodate slower reaction times. In essence, the communication time between neurons lengthens with age. Recent research by neurologist George Bartzokis at UCLA suggests that declines in the motor control cortex start far earlier than first suspected ' as early as age 40. As we age, the thickness of myelin, the insulation around our nerve fibers, decreases, and this affects the conduction rate of the signals the brain sends to muscle groups. By the time many motorists reach 65, there can be a significant increase in their reaction times. However, it is important for counsel to point out that it would be improper to generalize because research also confirms a wide variability in reaction times between older drivers. Those persons who have stayed active, both physically and mentally, can have markedly better reaction times than the average of their age cohort.

Behavioral Issues

Once physical impediments are ruled out, the analysis must then turn to psychological and environmental issues that might have contributed, in some fashion, to sub-par driving performance. Obviously, one must consider driving behavior patterns, which may compress the reaction time available to drivers. For example, it may be useful to consider issues such as:

• Tailgating;
• Improper lane changing;
• Disposition to excessive speeds; and
• Failure to yield right of way.

Opposing counsel will point out that any of the above conditions can reduce the reaction time needed for the plaintiff to take evasive maneuvers and that such behavior itself can contribute to accident causation.

Distraction Effects

The single largest category of effects that lengthen reaction times is grouped under the umbrella term distractions ' a simple term that encompasses a universe of issues and sources. Nearly every juror will be able to recall distractions during his or her own driving experience. Exactly how much distraction contributes to vehicle accidents is a matter of some debate. However, it is safe to state that distraction is a major contributor. A government funded $4.2 million study, carried out by the Virginia Tech Transportation Institute, tracked 241 drivers for over 42,000 hours of driving, and found that 80% of accidents could be attributed to driver distraction. Other studies have suggested lower percentages. A much earlier study (1970) at Indiana University of pre-accident factors found driver inattention was a leading cause of accidents. Moreover, the American Automobile Association rates 20%-50% of all accidents as having originated in driver distraction.

In recent years, much of the distraction debate has focused on cell phones with an estimated 85% of cell phone users admitting that they use their phones while driving. Persons operating vehicles, while using any form of cell phone, are adjudged to be as cognitively distracted (impaired) as persons who exceed the blood alcohol limits in all of the 50 states. However, a whole variety of other “cockpit behaviors” feed the distraction total. Eating while driving, intense conversation with passengers, and attention to on-board GPS systems are all well-known distractors.

The point is that each of these activities, as a result of both the physical and cognitive demands they impose on the driver, can significantly add to his or her normal reaction time. Unfortunately from an accident analysis standpoint, it is often difficult to determine exactly what distractors, if any, were present just before the accident. Cell phone records can provide a clue to that factor, and food and drink in the vehicle provide their own clues, but pinpointing other distractors is much more difficult. In a number of cases, the impact of episodic memory loss, triggered by a cascade of endorphins released into the brain at the time of accident-related physical trauma, makes it difficult for the defendant to describe to the analyst exactly what he/she was doing or thinking about just prior to the accident.

Tracing Reaction Potentials

What all of these distractions have in common is that they can adversely affect, i.e., lengthen, driver reaction times. To understand reaction times, it useful for jurors first to understand some of the basic neurological facts associated with our reaction to stimuli ' visual stimuli in the case of vehicle drivers. As light photons, containing multiple images of the traffic scene about us, enter the human eye, they fall on the light'energy-sensitive rods and cones of the retina on the back wall of the eye. The eyes' optical systems focus the image, the “target,” on the fovea, an area of the macula with a dense concentration of cone-shaped light receptors. The nerve messages are funneled through the fovea in the center of the eye and then passed back through the optic chiasm to a switching station further back in the brain, in the thalmus, the lateral geniculate nucleus, and thence to the visual cortex in the brain's occipital lobe. Other portions of the brain, e.g., thalmus, etc., then have a neural conversation among themselves (an obvious oversimplification) and pass a command message to the frontal brain lobe's motor cortex and then down the spinal cord to the appropriate muscle groups that act on the brain's command, e.g., lift your right foot off the accelerator and press on the brake, steer right, etc. All of this takes time ' a surprisingly long time when you consider that the driver is hurtling forward at speeds that sometimes exceed more than 100 feet per second. This is an area of understanding that jurors may fail to appreciate. Moreover, if a driver's visual acuity is compromised by cataracts, macular degeneration, diabetic retinopathy, etc., we can expect reaction times to be adversely affected. In addition, intrinsic brain disorders such as multiple sclerosis, tumors and stroke-related vascular damage will also impede signal travel time to and from the visual cortex.

As might be expected, things get more complicated as we further examine this process. Obviously, if the driver is substance- impaired, it will be argued that reaction times stretch out. However, they also stretch out for drivers who are fatigued, and they increase for drivers who have recently experienced some life-altering event, e.g., death of spouse, loss of job, interpersonal conflict, serious illness, etc. They may even differ depending on what time and day of the week an accident may take place (a compilation by Human Benchmark suggests 4:00 p.m. on Tuesdays is the worst.)

Types of Reaction Times

When we come to estimate reaction times, it is first useful to divide reaction time into two simple categories, i.e., simple reactions and choice reactions. We often encounter simple reaction times in conditioned reflex responses, ones in which neural response patterns, i.e., pathways, are already established or ones that we are alerted to expect to use. For example, as we approach a traffic'light-controlled intersection, and observe a green light, we can expect a change in the light signal from green to yellow to red. We do not have to think about what to do. We “automatically” brake when the light turns red.

Measuring Reaction Times

While there is no nationally recognized standard for simple response times for drivers (and given the variation in drivers' neurological attributes, there probably should not be), one of the most frequently cited ranges is 1.4 to 1.5 seconds. (In laboratory tests, humans can often react within 0.7 seconds ' but not in driving conditions). This a measure of the time span necessary for the light stimulus to fall on the retina to the subsequent time needed to initiate muscular reaction (application of mechanical force). That, however, is not the end of the reaction time equation. There is also the matter of latency. Simply pressing the brake pedal does not instantly result in the vehicle's brakes' taking hold. The vehicle's own “nervous system” must be accounted for. Hydraulic fluid must be energized, brake rotors activated, etc. Vehicle system latency can add an additional 0.3 seconds to the time between when the road obstacle, condition, etc., is seen and brakes applied and when the brakes begin to slow the vehicle's tire rotations.

Choice Reaction Times

It should be noted, however, that the average 1.4 -1.5 second reaction time is premised on simple reaction responses, scenarios in which there is little or no event surprise and where there is little choice option i.e., where alternative crash avoidance situations need not be considered, where the brain does not have to engage in choice decisions. In many accident scenarios, drivers will be dealing with choice reaction time, and these choice decisions do, as expected, lengthen reaction time ' but by how much?

A typical situation involves a stopped vehicle in a travel lane. Should the driver focus solely on coming to a stop behind the vehicle or both brake and try to steer around the vehicle? The closing distance, the rate of closure, the presence, or absence, of oncoming traffic in the opposing lane, etc., are all issues that the driver must weigh ' in fractions of a second ' and each of these considerations slightly increases overall reaction time.

Some research has suggested that, as the brain weighs various alternatives, recovers from event surprise, etc., such choice situations may even require a doubling of simple reaction times. A conservative estimate may have such reaction times increasing by at least one third. Thus, a choice reaction time would exceed 2.0 seconds.

Effect of Expectation

Reaction times can be shortened by expectation of a particular stimulus. In effect, the brain is put on notice ' alerted ' that in the immediate future the driver will be likely to encounter the need for a braking response and/or steering evasion maneuver. Consider, for example, roadside signs that announce:

• Danger: Deer Crossing Ahead.
• Caution: Falling Rocks.
• Warning: Bridge Freezes Before Road Surface.
• School Zone: Slow Speed Ahead.
• Beware: High-Density Traffic Area.

Such signage can ' and does ' affect driver behavior. Drivers intuitively reduce speed, increase the range of their vision sweep and prepare themselves, in a reaction sense, to take collision avoidance maneuvers. Such cognitive preparation can reduce the choice intervals in reaction times and drive reaction times more towards simple reaction time parameters. Of course, the lack of warnings can have an opposite effect. A surprise event, a deer bounding from behind a roadside hedge, a child dashing out from between parked cars, and so forth, may have such an element of surprise that reaction times may double from simple reaction time standards. Thus, in evaluating reaction times associated with a particular accident scenario jurors must be educated to take into account the issue of expectation and its likely impact on compressing or expanding reaction time parameters.

Combining Speed and Reaction Times

One of the crucial analytic questions that needs to be answered is: If the design defect is not the (entire) cause of the accident, could the driver have prevented this accident? To answer that question, the focus must shift to the distance point when the driver most likely first observed the obstruction ahead of him/her and whether, at any reasonable and legal speed, could the driver have stopped in time to avoid a collision? To derive physical constants, reconstructionists can work their formulas to provide speed estimates in the area just before vehicle impacts. The reconstructionist begins by attempting to determine the coefficient of friction (COF) of the road surface on which the accident took place. On dry asphaltic road surfaces, with normal tire tread, we can expect a COF of 0.8. On a rainy surface the amount of friction available decreases (the road gets more slippery) and the COF may drop to 0.7 to 0.6. To determine the COF the reconstructionist typically employs one of three methods. An accelerometer/computer may be mounted on the windshield or floor of a test vehicle(often a police cruiser), a test run initiated with a skid stop and a direct digital readout provided calculating the road surface's COF . It is also possible to use a portable Drag Box with a portion of a rubber tire mounted on its underside. The Drag Box is towed at a constant speed over the road surface and the resistance measured by an on-board gauge.

The reconstructionist may also choose to use a test vehicle that skids to a stop from a known initial velocity and the speed determined by measuring the length of the skid and entering that value, along with the velocity, into the formula:

2

' = V /255 S

Once the vehicle speed is estimated in MPH, the reconstructionist can then multiply this value times 1.4666 to determine the number of feet per second that the vehicle was traveling. For example, if the vehicle was traveling at 83 miles per hour, it would traverse 121.7333 feet each second. In such a scenario, with a 2.0-second reaction time, the driver would travel 243.4666 feet before he/she even applied the brakes. To this value the reconstructionist must then add the length of the skid marks to obtain the total distance between when the obstruction was sighted and the point of impact. Even at moderate speeds, e.g., 45 MPH (66 feet per second) a 2.0 second reaction time means that the driver will travel 132 feet before his/her foot even touches the brake pedal. Add in vehicle latency time and skidding distance, and it may take up to 200 feet to come to a full stop.

Conclusion

In summary, jurors may understand that there is not a lot we can do to improve human reaction times significantly. However, consideration of the many factors involved may demonstrate that the design defect was not the cause of the accident and the resulting injuries and damage.

E. Patrick McGuire is president of Padric Associates, a behavioral science research firm in Clinton, NJ.