A traffic accident is a highly involved, complex interaction between two objects. It includes a series of events that led up to the conclusion of the traffic accident. It is not simply a car hitting another object. To fully investigate a traffic accident, one must thoroughly understand, and evaluate what has occurred that caused, or contributed, to this event.

The reconstruction of a traffic accident must take into consideration there are various factors associated with all traffic accidents. To properly reconstruct a traffic accident, three essential and distinct factors must be investigated and documented in order to provide a well-founded explanation of the series of events prior to, during, and after a traffic accident. Today, we will discuss the first of these three, and most often under-investigated factors. The Human Factor.

Human Factors are associated with the individuals involved in the traffic accident. They include the driver and passengers but can also include bystanders. Factors include the individual’s distractions, use of alcohol or drugs, use of medications, medical events, fatigue, and the individual’s perception and reaction time (PRT). Most traffic accident cause classification systems have focused on the errors and actions of the participant that immediately led to the conflict. The actual reasons why human failure occurred are often not taken into account.

In 2015, the National Highway Traffic Safety Administration, a branch of the U.S. Department of Transportation, published a two-page memo declaring that “the critical reason, which is the last event in the crash causal chain, was assigned to the driver in 94% of the crashes.” The memo, which was based on the NHTSA’s own analysis of crashes, noted that traffic accidents are the result of many interacting factors.

In the “SUMMARY OF IMPORTANT FINDINGS” of a 1999 study prepared for NTHSA, “The Relative Frequency Of Unsafe Driving Acts In Serious Traffic Crashes”, the study determined the specific driver behaviors and unsafe driving acts that lead to crashes, and the situational, driver and vehicle characteristics associated with these behaviors. A sample of 723 crashes involving 1284 drivers was investigated. The crashes provided a fair sample of serious crashes involving passenger vehicles in the United States and in-depth data was collected and evaluated on the condition of the vehicles, the crash scene, roadway conditions, driver behaviors and situational factors at the time of the crash. The focus of the study was to determine the primary cause of each crash and uncover contributing factors.

In 717 of the 723 crashes investigated (99%), a driver’s behavioral error caused or contributed to the crash. There were six causal factors associated with driver behaviors that occurred at relatively high frequencies for these drivers and accounted for most of the problem behaviors. They were:

• DRIVER INATTENTION 22.7%
• VEHICLE SPEED 18.7%
• ALCOHOL IMPAIRMENT 18.2%
• PERCEPTUAL ERRORS (e.g. looked, but didn't see) 15.1%
• DECISION ERRORS (e.g. turned with obstructed view) 10.1%
• INCAPACITATION (e.g. fell asleep) 6.4%

DRIVER INATTENTION. The most dominant component of the causal factor pattern was driver inattention. Driver inattention indicated a lack of focus on the required field of view (typically forward). This definition encompassed both the driver inattention and driver distraction categories. Inattention was noted as the sole causal factor for a majority of the drivers who contributed to crash causation.

VEHICLE SPEED. The second largest component of the causal factor pattern was the vehicle speed factor. These typically reflected circumstances in which the driver was exceeding the speed limit and the absolute vehicle velocity contributed to crash causation.

It should be noted, however, that this causal factor was assigned in a small number of crashes where the vehicle's travel speed was at or below the posted speed limit. In these situations, the travel speed was inappropriate for prevailing weather/roadway conditions and contributed to a pre-crash loss of vehicle control (i.e., too fast for conditions). While the road conditions could be considered a separate causation factor, the driver’s inability to recognize the hazards associated with hazardous roadway conditions or weather is considered a Human Factor.

ALCOHOL IMPAIRMENT. Alcohol impairment was the third largest component of the causal factor pattern. In addition, the study found that alcohol impairment was a contributory factor in combination with other primary factors for many of the drivers.

PERCEPTUAL ERRORS. The fourth most frequently assigned causal factor involved perceptual errors associated with intersection crashes. Two specific scenarios were noteworthy:

(1) The subject driver checked for approaching traffic, did not see the other crash-involved vehicle (e.g., looked, did not see), and then attempted to cross or turn at the intersection.

(2) The driver checked for approaching traffic, saw the other vehicle, but then either misjudged the distance to that vehicle or misjudged the approach velocity of that vehicle (e.g., accepted inadequate gap to another vehicle).

DECISION ERRORS. The primary scenario in this group involved subject drivers who attempted to turn or cross with an obstructed view. While these situations typically reflected intersection crashes, there were a number of collisions which occurred at non-intersection locations (e.g., driver attempted to cross the roadway from a private/commercial driveway or attempted to turn into/exit a private/commercial driveway).

Additional causal factor types in this category included:

(1) violated a red traffic signal

(2) attempted to beat a phasing signal

(3) violated a stop sign

INCAPACITATION. Drivers who fell asleep or experienced a seizure/heart attack/blackout or other medical condition contributed to the causal factor pattern.

Past research has indicated the vast majority of traffic accidents are caused by human error. A landmark study by Indiana University (Treat, et al, 1979) found that Human Factors caused or contributed to 93% of the crashes investigated. The three major human factors most frequently reported in that study included:

• Improper lookout
• Excessive speed
• Inattention

Recent events illustrate the importance of human factors analysis in traffic accident reconstruction. One example is the 2018 Uber autonomous vehicle accident in Tempe, Arizona. The accident involved a woman who was walking her bicycle across the street when she was struck and killed by an Uber self-driving car. The National Transportation Safety Board (NTSB) investigation found that the vehicle's system detected the bicycle rider 5.6 seconds before impact. However, the driver was watching a video on her phone and not paying attention to the road. In-car video showed her gaze was re-directed from her phone about one second before impact. Driver steering input was determined to have occurred less than a second before impact, but the driver did not apply the brakes until about one second after the impact. The NTSB also identified several human factors that contributed to the accident, including the vehicle operator's inattention and over reliance on the vehicle's automated system.

The 2019 fatal crash involving a Tesla Model S in Delray Beach, Florida is another traffic accident that highlights the importance of evaluating the Human Factor.. The crash occurred when the vehicle, which was on autopilot, collided with a tractor-trailer that had crossed its path. The National Transportation Safety Board (NTSB) investigated the accident and found that the driver was not paying attention to the road and was relying too heavily on the vehicle's automated system. The NTSB also found that the autopilot system contributed to the accident by not detecting the trailer.

Another example is the 2019 crash involving a tour bus in Bryce Canyon, Utah, resulted in the deaths of four passengers and injured several others. The investigation found that driver fatigue contributed to the accident.

Probably the most infamous traffic accident where Human Factors was the primary cause of a traffic accident is the tragic death of Princess Diana at the age of 36 in a car crash on August 31, 1997. Princess Diana, along with her fiancé Dodi Fayed and driver Henri Paul, were killed when their Mercedes-Benz W140 slammed into a pillar in the Pont d’Alma tunnel in Paris France. The accident was attributed to a number of factors, including the behavior of the driver and the presence of paparazzi pursuing the vehicle. However, there were also several Human Factors that contributed to the accident.

Speeding

The high speed of the vehicle was determined to be a contributing factor. The Mercedes was traveling at a high rate of speed at the time of the crash estimated at 59 to 68 mph (95 to 110 kph). More than twice the speed limit of 31 mph (50 kph). The high speed was likely due to the pressure of being pursued by paparazzi.

Lack of Seatbelt Use

Investigators found that no one in the Mercedes were wearing seat belts at the time of the crash. This greatly increased their risk of injury and death in the accident.

Driver Intoxication

The autopsy of driver Henri Paul found an alcohol level of 0.175 g/mL (1.75 g/L), three times over the legal limit to drive. Prescription drugs also tested positive in the toxicology examination.

Failure to Maintain Control

The driver lost control of the vehicle, likely due to a combination of factors of high speed and driving while intoxicated, and the presence of paparazzi.

The 1999 French investigation determined high speed and driving while under influence of alcohol and prescription drugs was the primary factor in this traffic accident.

The tragic accident that claimed the life of Princess Diana was a stark reminder of the importance of Human Factors in traffic accidents. Speeding, lack of seatbelt use, failure to maintain control, and driving while under the influence can all contribute to the likelihood and severity of a crash.

Human Factors analysis can be challenging, as it requires a deep understanding of the human element of an accident. Accident reconstructionists must consider factors such as the operator's training, experience, and cognitive workload. They must also consider the interaction between the operator and the technology or equipment involved in the accident. Human Factors analysis is a critical component of accident reconstruction. Recent case studies highlight the importance of this analysis in understanding the causes of accidents and understanding how Human Factors are involved in a traffic accident.

As a professional in the field of traffic accident reconstruction, attending a specialized conference is an exciting opportunity to learn and network with other experts in the field. From April 17 through April 21, 2023, the World Reconstruction Exposition (WREX 2023) was held in Orlando, Florida. The conference was attended by a diverse group of professionals, including engineers, accident reconstructionists, law enforcement officers, and attorneys. In all, 1,268 people attended from 28 countries. 22 professional accident reconstruction associations were represented and over 100 training sessions were offered. WREX is held every six years with the first one held in Texas during the year 2000. I was fortunate enough to be one of 523 people that attended and WREX has since grown to be the world’s largest reconstruction conference.

At WREX 2023, the speakers included experts from various fields such as vehicle dynamics, biomechanics, accident reconstruction technology and reconstruction techniques. The speakers were from around the world and represented both the civil and private industry.

On the first day of the conference, the keynote speaker gave a fascinating presentation on the evolution of accident reconstruction “Then and Now”. Exploring how the science of accident reconstruction has grown from using tape measures and banker style stamps to diagram a scene, to the use of advanced techniques that includes computer programs, 3D scanning, and drones. The keynote address was followed by over 40 hours of technical session during the next 5 ½ -days with topics that included vehicle dynamics, photography techniques, human factors, advanced reconstruction techniques, and accident reconstruction software.

One of the most interesting sessions was on “Human Factors” associated with an accident reconstruction. The presenter is a world class researcher in the field and has devoted many years to understanding and developing the methods used to determine how human factors affect a driver during a traffic accident.

Another session that caught my attention was on the analysis of a vehicle’s tires after the accident. The speaker was extremely knowledgeable, not to mention very entertaining, and his eye-opening presentation on what to look for on a tire during a post-accident inspection can assist a reconstructionist to determine how or if the tires on the vehicle caused or contributed to the traffic accident.

Numerous break-out sessions were offered during the conference that allowed for small groups to speak with experts in the field on various subjects. I found the use of the iPhone in accident reconstruction particularly enlightening. Watching the instructor scan a crashed vehicle with an iPhone for use in a 3D modeling of that vehicle was fascinating and reminded me that the world of accident reconstruction is exploding at a tremendous rate.

The highlight of WREX 2023 was the crash testing that was conducted. 22 controlled research crash tests were conducted. 37 vehicles, including semi tractors, school buses, and passenger vehicles, were used in the testing and will provide over 3,000 photographs, videos, 3D scans, and 1,024 Gigabytes of data that was collected and will be provided to attendees. Crash testing also allows those who attend the opportunity to see the true mechanics of a traffic accident and helps to give a better understanding of the complexity of a traffic accident.

Throughout the conference, I had the opportunity to network with other professionals in the field, including accident reconstructionists, engineers, and attorneys from throughout the world. I was able to exchange ideas and learn from other professionals’ experiences and found these interactions to be extremely valuable.

Attending accident reconstruction conferences gives a deeper understanding of the field of traffic accident reconstruction. Attendees leave conferences feeling energized and excited about the future of this field, knowing that advancements in technology and investigative techniques are constantly being made.

Whether a large international conference such as WREX, or a small local conference hosted by a state association, attending a traffic accident reconstruction conference is an excellent opportunity for professionals in the field to learn and network with others. The conference I have attended in my career have provided me with valuable insights and a deeper understanding of the field of traffic accident reconstruction.

Traffic accident investigation and reconstructions can determine liability in the event of a traffic collision. Each day across the United States, people and machines react unexpectedly, causing thousands of traffic accidents claiming lives or causing permanent injuries. Of the over 6 million police reported traffic accidents in 2014, there were 29,989 fatal traffic accidents resulting in 32,675 fatalities in the U.S. Colorado alone had 544 fatalities in 2015, a rise of 56 fatalities over the 488 reported in 2014. Over 2 million people were injured with an economic loss estimated at over $242 billion.

When a traffic accident occurs, it is often not enough to simply say that something went wrong. A traffic accident investigation and traffic accident reconstruction can determine exactly what happened and can help prevent future traffic accidents. Additionally, traffic accident investigators can provide expert testimony in trials to hold the correct party accountable for the damage incurred by the traffic accident.

So why are people referring to a traffic “accident” as a “traffic crash”? According to the Merriam-Webster dictionary, an “accident” is defined as an unexpected and undesirable event, especially one resulting in damage or harm. Basically an unforeseen incident. A “traffic crash” is defined as colliding violently or to strike against something with great force, causing damage or destruction, or cause something such as a car to strike against something in this way.

The difference between an “accident” and a “crash” is an “accident” implied something that was out of your control and unavoidable whereas a “crash” describes a violent collision. A person who causes a traffic accident could have avoided the incident based on their decisions. It may as well mean for some unexplained reason, forces of the universe have met at a certain point in time and place and a result occurred that defies explanation. It means that it has likely never happened before and will probably never occur again in the future.

There are plenty of reasons why people turn to Traffic accident investigation:

• To determine what caused a traffic accident and prevent traffic accidents in the future.
• If you don't know what really happened in a traffic accident, you may be liable for damages and injuries. A good traffic accident investigator can prove that you were not at fault, save you long court hassles and thousands of dollars.
• To get answers. Sometimes, just knowing what really happened brings a sense of closure. A traffic accident reconstruction can tell you what really happened in a specific situation.
• To get evidence that can stand up in court. If you're trying to collect claims for a traffic accident or need to prove that you did not cause a traffic accident through negligence or other fault, only a qualified traffic accident investigator can help you get the evidence you need to solidify your court case.

What Happens In A Traffic Accident Investigation?

The police will investigate a traffic accident with the intention of determining if any criminal action took place in the traffic accident. Some of the things the police look for are speeding, hours-of-service violations, mechanical violations, alcohol use, drug use, etc. For example, if a truck driver is exceeding his hours of service and causes a serious traffic accident because he fell asleep at the wheel, he will likely be criminally charged. If that traffic accident results in a fatality, the charge will likely be vehicular homicide.

Depending on the nature of the traffic accident, a traffic accident investigation can include visits to the accident site as well as interviews with witnesses and with those involved. A traffic accident investigator will attempt to re-create exactly what happened so they can see exactly what took place and how. Today, this often is done with a variety of computer software programs. A traffic accident investigator may collect testimonies and other evidence, such as measure and document the scene with photographs and notes, that can help you determine exactly what happened in a traffic accident.

During the reconstruction stage, investigators will examine the point of impact, final resting positions, skid marks, scrub marks, and gouge marks. Electronic surveying equipment is typically used during this stage to recreate the traffic accident. The investigators may also inspect each vehicle beyond the damage it has suffered. Checking components like brakes, steering, tires, suspension, and lights may shed light on the cause of the traffic accident.

Traffic accident investigators reconstruct collisions for several reasons. The most important and yet more subtle reasons for looking into significant collisions is to identify any environmental factors that may have been a primary contributor to the collision. This may prevent additional collisions at a certain location from causing further injuries or fatalities. They are often the most easily and quickly remedied. Another benefit for examining these collisions is to identify any safety concerns in vehicles for equipment or structural failures. Although this prevents further unwarranted injuries or fatalities, these are less common and more difficult to see through to the end. Lastly, there is the investigation to determine fault or liability.

Often in vehicle collisions, the events can be foreseen, although not always observed. They can certainly be explained, and liability assigned. This happens daily in every city. In order to explain how an event occurred and why, a reconstructionists must seek causation. In doing so, contributing factors need to be considered in determining causation. These factors may include driver behaviors, environmental factors, and vehicular factors.

Once a roadway hazard is perceived by a driver, the driver reacts to the hazard, and physics takes over. There are one of two outcomes as a result. There is a collision or a collision avoidance. In the case of a collision, there is a multitude of factors that affect the outcome of the impact. The investigator must consider acceleration, braking, speed, friction, and direction, energy and momentum, all of which must be carefully analyzed. An effective reconstructionist has the unique ability and fortitude to compute many of these factors based on roadway evidence, scaled measurements, and sometimes recorded data.

Traffic Accident Reconstructionists are uniquely trained to take the investigation further into causation factors. Investigators consider many factors prior to and after the collision, as well as, being trained to meticulously explain the details of a collision itself, where more events occur in 1/10th of a second than most can imagine.

For example, in a scenario where two vehicles collide at an intersection, a reconstructionist is interested in the pre-collision events. Where were the drivers traveling from? Where was their intended destination? What was their frame of mind at time of departure? What do the cell phone records reveal prior to the collision? In addition, and all too often, were the driver’s intoxicated?

Once these questions can be answered, the next issue at hand is the scene of the collision.

Hopefully, this is where the responding police department has protected the scene for preservation of evidence and, subsequently, conducted a thorough investigation by obtaining all possible witness statements, marked any and all roadway evidence, and successfully measured the scene using a total station or other scene mapping equipment. These and others are all vital requirements for a successful private practice reconstructionist to review the case and identify any factors that may be important to a civil or criminal case. One rule to keep in mind is there is very seldom evidence not tampered with from bystanders or other emergency personnel whose primary job is not to preserve evidence but save lives.

While reviewing the results of the investigation or revisiting a scene, a reconstructionist must look for environmental factors such as was the sun at a position to blind a driver’s view, are there trees or other objects blocking a view of traffic, was the traffic regulating equipment working properly. We can then begin to look at the roadway makeup and condition at the time of the collision. Another factor to consider is contributing vehicle factors by the units involved. Are there any vehicle recalls and have the repairs been completed by an approved mechanic? Have there been any recent collisions that may have caused prior damage to a vehicle that made this specific wreck worse than it should have been? Was the vehicles equipment operating properly at the time of the collision?

In addition to these telling details is the vehicle damage. There is a very accurate story told by the damage that often cannot be altered. The principle direction of force (or PDOF) will fold a vehicles exterior in the direction the collision occurred.

Traffic Accident Reconstructionists can also tell which lights were on during a collision, even if they are off once the collision occurs (an affect called “hot shock”).

In the case of law enforcement investigations, often a driver who wishes to avoid the fact that he was driving can be identified by a foot print left on a brake or accelerator pedal. A Traffic Accident Reconstructionist must look at how law enforcement identified a person as the driver so appropriate liability can be assigned.

Why hire an ACTAR accredited reconstructionist?

ACTAR is a term frequently seem when looking for a Traffic Accident Reconstructionist. So exactly what is an ACTAR accredited reconstructionist? ACTAR is an acronym for the Accreditation Commission for Traffic Accident Reconstruction, an internationally recognized commission with more than 1260 ACTAR Accredited Reconstructionists practicing throughout the United States, Canada, Australia, Singapore and the United Arab Emirates.

From their website, ACTAR was founded by and exists for the benefit of the traffic accident investigation and reconstruction community, as represented by the membership of the participating professional organizations.

Since its incorporation in 1991, it has been the ongoing goal to promote, within the legal and scientific community, a recognition of the minimum standards established by the NHTSA study, as well as those developed by an ongoing review of the latest technology and trends in the profession.

Minimum standards have been designed to advance the recognition of the ACTAR accreditation program, and to encourage the integrity, consistency and professionalism of those involved. ACTAR aims to promote the professional and intellectual development of those individuals, organizations and institutions involved in traffic accident investigation and reconstruction and to assist the legal and scientific community in weighing the suitability of individuals offering their services as Traffic Accident Reconstructionists.

So how does a Traffic Accident Reconstructionist become accredited?

A reconstructionist must apply to the commission and meet minimum standards of education and experience. If the standards are met, the reconstructionist must successfully complete a practical and a theoretical examination to be accredited.

The examination consists of two parts, a Theory portion and a Practical portion. The Theory portion consists of 75 questions drawn from areas such as Kinetic Energy, Conservation of Momentum, Time-Distance Evaluations, Physical Evidence from the road and vehicle, Photography, Lamp Analysis and Airborne Analysis.

The Practical portion is a staged collision where the candidate is supplied with photographs of the scene and involved vehicles, vehicle data and damages, location and type of physical evidence and a skeleton diagram. The candidate is asked to provide impact and departure speeds, angles, Delta-V for each vehicle and identify specific physical evidence.

Although participation in the accreditation program is voluntary, people who are properly trained and experienced in Traffic accident investigation and reconstruction can successfully complete the examination and achieve accreditation. Those accredited must obtain a minimum number of continuing educational units (CEUs) over a five-year period from completion of the initial examination to maintain their status with ACTAR.

An ACTAR accredited reconstructionist has demonstrated their training and knowledge before a peer group organization and must maintain a high level of training and experience top become accredited and to maintain their accreditation.

By hiring an ACTAR accredited reconstructionist, one is assured that the individual follows the highest standards of training and the ACTAR Code of Conduct to provide an unbiased, efficient and compete traffic accident reconstruction available.

Mj Investigations, LLC. offers an ACTAR accredited reconstructionist (ACTAR #1084) with over 35 years of experience. Accredited since the year 2000, Mj Investigations Traffic Accident Reconstructionist will provide the training and experience of investigating and reconstructing thousands of traffic accidents in five states and providing expert testimony.

As you can see, a solid collision investigation can fill a large file of detailed reporting by someone who has received the proper training and has obtained the right experience for the needs of a client. Mj Investigations, LLC investigators have responded on scene to thousands of collisions, many fatal, and have had the unique opportunity to observe the evidence minutes after the collision has occurred. Mj Investigations, LLC investigators have law enforcement backgrounds, experienced in civil depositions and testimony, as well as, successful criminal cases.

A physicist or an engineer can calculate data or explain the damage to vehicles based on principles and graphs, but Traffic Accident Reconstructionist have the first-hand experience that gives clients the edge in a successful case. Mj Investigations, LLC training has come from nationally prominent authorities in the field of traffic accident reconstructions and investigations and our experience has come through being at the scene of every type of incident our clients may incur from single vehicle to a passenger car vs. commercial vehicle. If there is a need for commercial vehicle inspections, Mj Investigations, LLC is able to provide them when needed for an investigation at varying levels. In addition, Mj Investigations, LLC has the availability to image event data recorders to obtain collision information such as seat-belt use, braking indicators, speed, airbag deployment, and much more.

The term “Drag Factor” is utilized in traffic accident reconstruction. This term is not mentioned in engineering mechanics or physics books. Drag Factor is the deceleration coefficient for an entire vehicle. The Coefficient of Friction is the deceleration coefficient for a sliding tire. The Drag Factor and Coefficient of Friction are the same, if and only if, all four tires on a motor vehicle are locked and sliding on a level surface.

For years police officers have been taught these two terms were the same thing and for the sake of simplicity, we will use the terms interchangeably and say they mean the same thing for the purpose of this discussion. In this article, the drag factor, or coefficient of friction, basically measures the stickiness of a surface such as a roadway, a grass knoll, a ditch, and the like.

So why does an accident investigator need to know what the drag factor of a roadway surface is and how do they use it? Each surface has its own drag factor, which will determine how quickly a vehicle can come to a stop and how far it will travel while doing so. This answers the question; “How fast were they going?” Probably the most common question heard when an accident investigator is retained for a case.

In an accident investigation, this stickiness of a surface is assigned a number and is denoted with an f. Drag factors can be determined a number of ways. The use of tables and charts published by accident-investigation authorities, and based on thousands of tests, is the most common.  These charts have been validated in court and are used worldwide. They are available from a number of sources, both in print and online.

The use of a drag sled is also common. A drag sled is basically a box that is a known weight; it is pulled at a known force, and the drag factor of the surface can be calculated. These devices can be purchased premade, or they can be made by the investigator. 

A skid test using a similar vehicle, if possible, can be completed. The vehicle is driven at a known speed, and then a hard-braking maneuver is completed to obtain skid marks. These skid marks are measured, and a drag factor can be calculated.

Various scientific instruments (for example, the VC-3000) can be used to determine the drag factor of a roadway surface. These devices began in the research field and the drag racing world and can be purchased for about $1,500.

Knowing the coefficient of friction of a roadway is important as this factor will affect the accuracy of the speed calculation. Let’s take a simple example of a vehicle sliding on the roadway. The vehicle left 4 skid marks that were measured and an average skid of 200 feet was determined. The investigator presumed the roadway was new asphalt and decided it had a coefficient of friction of 0.8 by using the standard chart of coefficient of friction for various roadway surfaces. Using the basic slide to stop formula and the investigator’s coefficient of friction the minimum speed is calculated at 69.2 MPH.

It was later determined the roadway was actually, Portland cement that was over 10 years old and heavily traffic polished. Portland cement that is traffic polished has a coefficient of friction of around 0.55. Using this coefficient of friction the minimum speed is calculated at 57.4 MPH. A difference of aboout 12 MPH.

There are additioanl variables that will affect the calcualtions but this article is not about speed calculations. The investigator must keep this in mind and remember that an accurate coefficent of friction, or drag factor, is important when trying to determine how fast a vehicle was traveling prior to a traffic accident.

Tire marks are probably the most often confused and misinterpreted of all roadway evidence. A tire mark is the general class of marks left by a tire, whether rolling or locked. A skid mark is left by a locked, sliding tire.

There are different types of tire marks associated with a traffic accident investigation. The most common a private investigator will observe are:

• Scuffs: made by a rotating or yawing vehicle, a vehicle acceleration, or a flat tire
• Yaw mark: made by a tire that is rotating and sliding sideways parallel to that wheel’s axle; also referred to as sideslip or critical-speed scuff marks
• Skids: made by a locked wheel caused by the application of the brake
• Prints: made by a rolling tire
• Scrub mark: left by a wheel locked due to damage

Skid marks are further identified in the following ways:

• Pavement grinding: caused by material embedded in the tire grinding along the surface of the roadway (can be hard to see)
• Tire grinding: caused by the tire itself being ground by the abnormalities of the road surface (can also be hard to see)
• Erasure: caused by a sliding and locked tire erasing or removing any loose materials from the road surface so that area appears clean (this is frequently seen but is the most commonly ignored skid mark)
• Squeegee: caused in a similar way as erasure and removing moisture
• Soft foreign-material smear: caused when snow, mud, or soil that has been smoothed or spread

• Bituminous material smears: caused when a tire is hot enough to smear tar and asphalt (the most commonly measured segment is referred to as a skid mark)
• Tire smear: caused when a tire is hot enough to smear the rubber from the tire; usually seen on concrete surfaces
• Shadow: the part of a skid occurring prior to any pavement grinding; supposedly always present; more often than not extremely difficult to detect; and almost always very difficult to document or image
• Skip skids: caused by deformities in the road surface, or a vehicle weight shift
• Gap skids: caused when releasing and reapplying brakes during a skid
• Furrow: caused by a sliding, non-rotating wheel creating a plowed depression in soft material so that material furrows on each side; no tire print is visible
• Rut: caused by a rolling tire in soft material; the tread pattern is usually visible
• Acceleration marks: typical scuff mark made when sufficient power is supplied to the driving wheels and at least one-wheel spins on the roadway surface; begins as a J-shaped mark, caused by initial fishtailing as the tires heat and seek traction; the beginning of the scuff is usually very dark, and the mark gradually disappears
• Roadway art: produced when drivers back up and then shift gears to move forward before they have stopped going backward
• Flat tire scuffs: made by a seriously underinflated or overloaded tire; a partially deflated tire produces marks that are heavy on the edges and light in the middle; with a completely deflated tire, the sidewall touches the roadway, causing scalloped and wavy marks, and rim cuts are commonly seen.
• Scuff Mark: a tire mark from a wheel that is both rotating and slipping: acceleration scuffs, yaw marks, flat-tire marks.
• Scrub Marks: a skid mark caused by the vehicle being redirected as a result of a collision; marks generally look like irregular shaped smears and are characteristic of the point of impact

The proper identification of tire marks is an important part of an accident investigation. Each tire mark is produced by a specific action of the vehicle during the traffic accident event. Tire marks can tell the private investigator about what a driver did or attempted to do prior to and after a collision. A point-of-impact (POI) or an area-of-impact (AOI) can determined which is an extremely important part of the traffic accident investigation.

The proper interpretation of tire marks can tell the private investigator which, of the many, speed calculation formula to be used. For example, a vehicle left a 150-foot tire mark on a paved roadway prior to running off the road. If the tire mark is identified as a yaw mark and the specific formula for that type of mark is used, a speed calculation of 48 mph is determined. That same mark if identified as a straight skid will yield a speed of 56 mph. An 8-mph difference may not mean much unless the posted speed limit is 40 mph.

Collision-Avoidance Systems

Once in the realm of science fiction, it seemed incredible that a vehicle would be able to “see” other vehicles or pedestrians, anticipate collisions, automatically apply the brakes or take corrective steering actions and even drive itself. But this advanced technology is becoming increasingly available and more cars can do this to some degree.

Some of these systems have been around for a few years, mostly on high-end luxury cars. Collision-avoidance systems are getting better and are rapidly becoming a standard addition to new cars and not just a high-end option.

The Insurance Institute for Highway Safety (IIHS) has added collision-avoidance system testing to its suite of safety evaluations. They have determined that some of these collision-avoidance systems could prevent or mitigate many crashes. To win a top overall safety score, a car needs to have a forward-collision warning system with automatic braking and any autobrake system has to function effectively in formal track tests. To view the test results or to check if a vehicle has collision-avoidance systems available, visit the IIHS website at: www.iihs.org/iihs/ratings/crash-avoidance-features.

National Highway Traffic Safety Administration (NHTSA) is considering making some collision-avoidance systems mandatory. NHTSA’s 5-Star Safety Ratings note which systems are available on cars they crash-test but their presence doesn’t affect the rating. The cost of collision-avoidance systems can still be an obstacle with most advanced systems being part of a large options package or on a model’s higher, more expensive trim versions. The options can add thousands of dollars to a vehicle’s price.

Lasers, Radar, and Cameras

These active safety systems rely on numerous sensors, cameras, lasers, and short- and long-range radar which monitor what is going on around the vehicle. Other vehicles, pedestrians, cyclists, as well as the vehicle itself and even road signs are all monitored. Data is processed by computers, which then prompt an action from the car or the driver. These actions may start with attention-grabbers, such as a beep, a flashing dashboard icon, a tug from the seatbelt, or a vibration in the seat or steering wheel and if the driver doesn’t respond, the more advanced systems then apply partial or full braking force. Research has found that when a warning system emits too many inappropriate alerts, then there is temptation to switch it off.

Not every system on the market today is top-notch. But there’s a net benefit regardless. Even if the systems fail to prevent a crash, that crash is going to be less severe than it would have been otherwise. These systems can prevent crashes from happening in the first place.

Adaptive Cruise Control (ACC)

ACC allows the driver to select the cruise control speed and following gap. ACC detects if there is a vehicle in your path and either accelerate or brakes to maintain the selected following distance. If ACC cannot apply sufficient braking because of approaching a vehicle too rapidly, ACC will alert the driver.

Rear cross-traffic alert

Cross-traffic alert warns you of traffic approaching from the sides as you reverse. The warning usually consists of an audible chirp and a visual cue in either the outside mirror or the rear camera’s dash display. The more advanced systems can also pick out bicycles and pedestrians.

Forward-collision warning (FCW) and autobrake

Also called a pre-crash warning system, these systems warn drivers of an impending collision by using visual, auditory, or physical cues. Most vehicle systems also pre-charge the brakes and take other steps to prepare for impact. If the driver ignores the warnings, systems with autonomous braking, or autobrake, will apply partial or full braking force. They can be active at anywhere from walking to highway speeds.

Blind-spot monitoring (BSM) and assist

A blind-spot monitoring system uses radars or cameras to scan the areas beside and behind you, looking for vehicles entering or lurking in your blind zones. When such a vehicle is detected, an illuminated icon appears in or near the appropriate side-view mirror. If you signal a turn while a car is in your blind zone, some systems send a stronger alert, such as a blinking light or louder chirps. More advanced systems help keep you in your own lane by applying the

brakes on one side of the vehicle.

Pedestrian detection and braking

Pedestrian detection can recognize a person straying into a vehicle’s path. Some will automatically apply the brakes and newer systems can also detect bicyclists.

Adaptive headlights

As you turn the steering wheel adaptive headlights will swivel, which helps illuminate the road when going around curves. Adaptive headlights improve a drivers’ reaction times by about a third of a second, just enough to avoid hitting a parked car or animal on a dark road.

Lane departure warning (LDW) and assist LDW

These systems use a camera, along with various sensors, to identify lane markers and monitor your distance from them. If you stray over the line without signaling, you’ll hear a warning tone, an LDW warning in the instrument panel or perhaps a physical alert like a vibration in the steering wheel or seat.

Lane departure warning does not provide a warning to help avoid a cash unless it detects the lane markings. More advanced “lane keeping assist” (LKA) systems selectively apply brakes or nudge the steering to guide you back if you’re wandering.

Automatic park assist

The system will identify a parallel or perpendicular parking space your car can fit into. Once found, the system steers the car into the space; some can also exit from parallel parking

spaces. The driver still does the braking and has to follow commands from the system.

Rear cameras and parking assist

Rear-view cameras will be mandatory with the 2018 model year. They can help prevent a back-over accident, such as hitting a child who wanders behind your car. Parking assist sensor systems notify you with progressively louder and quicker beeps as you close in on an obstacle.

1. View displayed by the camera.
2. Corners of the rear bumper.

Knowing what collision-avoidance systems a vehicle may have and what they are designed to do is within the realm of the private investigator. Due to the growing list of collision-avoidance systems the investigator must consider this advanced technology as part of their investigation. By researching the vehicle involved, the investigator can determine the type of systems a vehicle is equipped with. Understanding what the systems are designed to do can assist the investigator in discovering other factors involved in a traffic accident. These questions can become important for the client or the attorney.

Questions for the investigator to consider include:

• What is the vehicle equipped with?
• What is the system designed to do?
• Did the system work properly?
• Was the driver provided a warning of the potential hazard?
• Did the driver respond to that warning?

The investigator can check the IIHS website: www.iihs.org/iihs/ratings/crash-avoidance-features or contact the local vehicle manufacture dealership to get information about the systems a vehicle may have and what they are supposed to do.  

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 A picture is worth a thousand words. This is especially true in a traffic accident investigation. Photographing the scene of a traffic accident is probably the second most requested task that a private investigator will receive from a client. An important part of accident investigation is recording information so that it can be used later. Photography is an indispensable means of achieving this.

Photographs are employed in two ways; to create a permanent, accurate, unbiased record of something specifically observed by an investigator and to capture the detailed appearance of something such as a mark on the road or damage to a vehicle. Photographs may later reveal significant details that were not observed at the time the picture was made.

Obtain the police photographs, if any, and then ask yourself: what should I photograph? Remember, your photographs need to tell a story. We are a highly visual society, and people have a difficult time understanding complex actions and ideas without something to look at to help them understand. This is especially true with juries. Think of what the story is and how you would explain it to a jury using only the picture you took.

If you know, either by measurements or police photographs, the final position of the vehicles or bodies, photograph their positions at final rest. Include recognizable landmarks that help identify the location of the accident. The driver and witness points of view established what they saw or could have seen based on the surrounding visibility. Attempt to locate the point-of-impact (POI) and photograph its location and the views to and from that point. Utilizing an overhead view or map can assist with locating their position. Have the witness mark their location on the map which will assist with establishing their point of view.

If you are photographing the vehicles at a tow yard, use a minimum of the four-corner approach.  This captures all sides of the vehicle, for a complete exterior view. If you can gain access to all sides of the vehicle and the interior, take additional shots. Work systematically, moving circularly around the vehicle. Photograph the front and the back, especially the license plate. Don’t overlook the VIN plate or NADAR sticker to identify the vehicle. Take interior shots, especially if you are trying to show the damage and how it relates to the occupants. Watch for sharp edges when completing interior shots.

On scene, take photographs of the approach path of each vehicle to include sight lines and any obstructions, temporary or permanent. Also take photographs from the advantage points of witnesses. If taking close-up shots of vehicles or evidence, take a pull-back shot so the close-up shot can be orientated to the pull-back shot; use a ruler or other object of known size to orient the evidence by size.

What kind of camera should you use? This depends on what you plan to use it for. The more technical the work, the more high-end your camera should be. Digital cameras of at least 10 megapixels are best. A quality digital camera can be purchased for as little as $50, and you can take as many pictures as you need without worrying about printing costs. Digital cameras also provide instant viewing, either through the screen or by downloading photographs to a laptop. There is nothing worse than taking a huge number of photographs and then finding out you have no film in the camera or the pictures are out of focus. You can also take hundreds, if not thousands, of photographs on a single eight gigabyte SD card.

Your camera should have an autofocus function as well as a manual focus. Auto-focus is good for that quick shot you need to quickly take before a truck runs you over. Manual focus helps you get the close-up shot without the auto-focus locking in on something in the background. Most digital cameras have a zoom feature. Zoom is good for focusing on small items such as tears, hair, blood spatter, and so on. A macro feature is also good for focusing on those small items.

Automatic focusing is not ideal when taking nighttime photographs. A good flash, either external or part of the camera, is also useful to have, but watch for washout caused by the flash hitting a reflective surface. Flash is also good for highlighting detail in a shot. Nighttime photography is difficult, at best. A high-quality camera with a high-quality external flash is best for nighttime shots. With an external flash and a sturdy tripod, an investigator can “paint the scene” with the flash. Watch for reflective surfaces or bright lights and objects in the background. Auto focus will try to focus on these and your main object will be blurry.

Point-and-shoot cameras and auto-focus are good for most photographs you take on a scene. But learn the basics of manual operation of your camera. Knowing how to manually access the settings on your camera will provide quality photographs of the scene that can be used in your case. Learn the “exposure triangle” and how the ISO, aperture, and shutter speed affect one another.

I highly recommend taking a photography class. There are a number of classes, both in person or online, that readily available and most are very inexpensive or free. Professional instruction will help with the proper methods for taking quality evidentiary shots. A quality camera and tripod are a necessity and foremost, know how to use your camera before you go to the scene. Many investigators have arrived on a scene and try to learn how to use their camera while they are there. Make sure your camera battery is charged and have a spare battery. Choose a camera without internal memory. Instead, use quality SD cards and have a backup to your back-up when the pictures are downloaded. Caution should be exercised if you use a cell phone, as it can be taken as evidence, and that includes everything on it.

If you are using a video camera as part of the scene photography, be aware of the audio portion. Watch what is said by either you or your assistants. Make sure people are not in the shot unless it is necessary and no horseplay, as that embarrassing part may be seen by a jury. 

If you have any doubt if something should be photographed, take the picture. As with measurements, it is better to have too many and not need them than to have too few and need them. Practice, practice, and practice. Try taking pictures of different objects at different angles or distances. Use the manual settings to discovery how they will improve your picture taking. Use different light sources and from different angles. Imagine what you will need to photograph at a traffic accident scene and take pictures before you need to complete a set of photographs for a client.

A while ago, I listened to a podcast about vetting an expert witness. I’ve testified as an expert in numerous cases throughout the U.S. and after listening to this podcast, it became clear that most accident reconstruction experts do not get vetted by the attorney hiring them. With no official accident reconstructionist certification, anyone can, and they do, advertise themselves as conducting traffic accident reconstructions. While many are professional private investigators, being a PI does not give them the training and experience to be an accident reconstructionist.

Vetting your expert to ensure they are knowledgeable and will provide a comprehensive and accurate reconstruction is important when choosing who you will retain.

The first step is deciding what kind of expert you need. There are four main types of experts in the field of traffic accident reconstruction.

1. The Reconstructionist:
   1. This individual has received extensive training and is accredited as a reconstructionist and usually comes with a background in law enforcement. The reconstructionist has been on live traffic accident scenes and has done this as a full-time job.
   2. A Reconstructionist takes a scientific approach to analyze a traffic accident to a deeper level than a first responding officer will. And they will dive deeper into looking at the causation of the collision.
   3. A reconstructionist is skilled in locating and interpreting physical evidence from a traffic accident.

2. Engineers:
   1. This individual has completed a course of study in engineering through an accredited university.
   2. They typically focus on mechanical engineering.
   3. There are two types of engineers who perform traffic accident reconstructions. Those who have gone to training to get a traffic accident reconstruction certificate. Some engineers will complete additional training, but most do not..

3. Biomechanical Engineers:
   1. An off shoot of mechanical engineers. Many lump them in with engineers but biomechanical engineering applies principles of mechanical engineering to biological systems and stems from the scientific discipline of biomechanics.

4. Occupant Kinematic Experts:
   1. They are not a biomechanical engineer.
   2. Involves the study of occupant motion inside of a vehicle during a traffic accident.
   3. Perhaps the best description for this area of study is occupant motion.
   4. Most are reconstructionist that have done additional training on how a body moves in a traffic accident.

The main difference between a reconstructionist and an engineer is the ability to locate and interpret evidence. An engineer largely has only theoretical classroom experience, and few have been on the scene of an active traffic accident investigation. If they continue to a reconstruction school, they only see evidence in a controlled environment, in photographs, or video. They are never taught how to locate evidence on a live scene.

An Engineer typically receives 875 hours of course instruction, 105 of those hours can be related to traffic accident reconstruction. A Traffic Accident Reconstructionist completes a minimum of 600 hours of instruction by the time they can qualify for ACTAR. Forty hours of that training carries over into the engineering field.

ACTAR is the Accreditation Commission for Traffic Accident Reconstruction. Founded in 1991, ACTAR exists for the benefit of the traffic accident investigation and reconstruction community. The primary goal of ACTAR is to promote within the legal and scientific community the recognition that an ACTAR accredited traffic accident reconstructionist has demonstrated competence with respect to the minimum training standards.

When you have decided what kind of traffic accident expert you need, then the vetting process begins to ensure this expert is the “right” expert. Here are 12 questions to help when speaking with your potential expert.

1. What is their tone & pace?

Is the expert enthusiastic about his field? Do they sound excited about your case and their ability to help you?

2. Are they sharp as a tack?

Do they sound intelligent and get to the point? Do they sound confident, and do they sound like they know what they are talking about?

3. Do they sound like someone worth listening to?

They will be guiding the jury through the events, basically giving a guided tour of the traffic accident. Will they be able to paint this picture with words not only in their report, but will they be able to provide testimony that the jury will understand?

An expert that speaks at an academic level above a jurist will hinder your case. However, equally as important, if not more so, can your expert testify without losing your jury? Will they be testifying over their heads? When looking at your jury during the expert’s testimony, you do not want to see the “deer in the headlights” look.

4. Is their tone and pitch pleasing to the ear?

Does the tone or cadence of their voice cause the jury to tune out? The expert must be able to speak coherently and able to keep the jury’s attention for an extended period of time.

5. Do they stress different points with different tones and inflections?

          A monotone is a sure way to make a jury tune out your expert or worse yet, fall                asleep during their testimony.

6. Did they build a rapport with you?

This should occur during the first time you speak with them. If they didn’t establish a rapport with you, they will not build it with the jury.

Is the expert likeable? Can they relate to the jury, or will they alienate them?

7. Was the first telephone call conversational or transactional?

Was there dead air in the call? This will translate to dead air while testifying.

8. Were there noticeable filler words?

Ummm, well, etc. These give the impression the expert does not know what they are testifying to and are trying to think up an answer.

9. Would you be convinced by them?

Do they know their field, or have they done enough research to know what to say? Do they have experience in the type of case they are testifying to?

10. When reviewing their Curriculum Vitae (CV), do they have the street cred for what you need?

Does your expert have current certificates that show they are continuously learning the latest topics in traffic accident reconstruction?

11. Have they withstood a court challenge before?

         Withstanding a court challenge gives the expert credibility.

12. Have they ever been paid to instruct a class?

They are basically teaching the jury a class. Being paid to teach a class indicates others are willing to pay for the knowledge they hold.

13. Have they ever been paid to be a public speaker?

If so, they are typically a dynamic person who people are willing to pay to hear what they  have to say and hopefully learn from.

14. Did they teach you something on the call?

Did you walk away from the call learning something you didn’t know before? Did the expert provide the knowledge to you easily?

15. Can they submit a sample work product?

Is it complete and easy to understand? Did the layout make sense and follow a logical flow? Did they include photos and graphics? Was the scope of their report clearly defined? Will readers be able to understand what happened in the traffic accident and why?

Not many juries have scholars that can understand the technical processes and scientific theories involved in a full traffic accident reconstruction. Albert Einstein is often credited to have said, “If you can’t explain it simply, you don’t understand it well enough.” Will your expert be able to “explain it simply”? If your jury doesn’t understand your expert, then they don’t understand what occurred in the traffic accident. And an expert that talks above a jury’s ability to understand often comes across as a “braggart and pretentious” and one who thinks they are better than the jury.