Main Encyclopedia of Forensic Sciences
Encyclopedia of Forensic SciencesPekka J. Saukko, Jay A. Siegel, Geoffrey C. Knupfer, Pekka J Saukko
The Encyclopedia of Forensic Sciences is the first resource to provide comprehensive coverage of the core theories, methods, techniques, and applications employed by forensic scientists. One of the more pressing concerns in forensic science is the collection of evidence from the crime scene and its relevance to the forensic analysis carried out in the laboratory. The Encyclopedia will serve to inform both the crime scene worker and the laboratory worker of their protocols, procedures, and limitations. The more than 200 articles contained in the Encyclopedia form a repository of core information that will be of use to instructors, students, and professionals in the criminology, legal, and law enforcement communities.
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Geoffrey Knupfer , National Training Center for Scientific Support to Crime Investigation, Harperley Hall, Crook, UK Pekka Saukko , University of Turku, Finland Description The Encyclopedia of Forensic Sciences is the first resource to provide comprehensive coverage of the core theories, methods, techniques, and applications employed by forensic scientists. One of the more pressing concerns in forensic science is the collection of evidence from the crime scene and its relevance to the forensic analysis carried out in the laboratory. The Encyclopedia will serve to inform both the crime scene worker and the laboratory worker of their protocols, procedures, and limitations. The more than 200 articles contained in the Encyclopedia form a repository of core information that will be of use to instructors, students, and professionals in the criminology, legal, and law enforcement communities. Audience Forensic science laboratories, police departments, academic libraries, law firms and law school libraries, academic departments teaching forensics, government agencies, and public libraries. Contents CONTENTS: Accident Investigation (a) Aircraft. Accident Investigation (b) Motor vehicle (including biomechanics of injuries). Accident Investigation (c) Rail. Accident Investigation (d) Reconstruction. Accident Investigation (e) Airbag related injuries and deaths. Accident Investigation (f) Determination of cause. Accident Investigation (g) Driver versus passenger in motor vehicle collisions. Accident Investigation (h) Tachographs. Accreditation of Forensic Science Laboratories. Administration of Forensic Science (a) An international perspective. Administration of Forensic Science (b) Organisation of laboratories. Alcohol (a) Blood. Alcohol (b) Body fluids. Alcohol (c) http://www.elsevier.com/wps/find/bookdescription.cws_home/673576/description#descri... 06/03/2005 Elsevier.com Página 2 de 4 Breath. Alcohol (d) Post-mortem. Alcohol (e) Interpretation. @con:CONTENTS: Alcohol (f) Congener analysis. Analytical Techniques (a) Separation techniques. Analytical Techniques (b) Microscopy. Analytical Techniques (c) Spectroscopy. Analytical Techniques (d) Mass spectrometry. Anthropology: Archaeology. Anthropology: Skeletal Analysis (a) Overview. Anthropology: Skeletal Analysis (b) Morphological age estimation. Anthropology: Skeletal Analysis (c) Sex determination. Anthropology: Skeletal Analysis (d) Determination of racial affinity. Anthropology: Skeletal Analysis (e) Excavation/retrieval of forensic remains. Anthropology: Skeletal Analysis (f) Bone pathology and ante-mortem trauma in forensic cases. Anthropology: Skeletal Analysis (g) Skeletal trauma. Anthropology: Skeletal Analysis (h) Animal effects on human remains. Anthropology: Skeletal Analysis (i) Assessment of occupational stress. Anthropology: Skeletal Analysis (j) Stature estimation from the skeleton. Art and Antique Forgery and Fraud. Autoerotic Death. Basic Principles of Forensic Science. Biochemical Analysis (a) Capillary electrophoresis in forensic science. Biochemical Analysis (b) Capillary electrophoresis in forensic biology. Blood Identification. Blood Stain Pattern Analysis and Interpretation. Causes of Death (a) Post-mortem changes. Causes of Death (b) Sudden natural death. Causes of Death (c) Blunt injury. Causes of Death (d) Sharp injury. Causes of Death (e) Gunshot wounds. Causes of Death (f) Asphyctic deaths. Causes of Death (g) Burns and scalds. Causes of Death (h) Traffic deaths. Causes of Death (i) Systemic response to trauma. Causes of Death (j) Poisonings. Cheiloscopy. Clinical Forensic Medicine (a) Overview. Clinical Forensic Medicine (b) Defence wounds. Clinical Forensic Medicine (c) Self-inflicted injury. Clinical Forensic Medicine (d) Child abuse. Clinical Forensic Medicine (e) Sexual assault and semen persistence. Clinical Forensic Medicine (f) Evaluation of gunshot wounds. Clinical Forensic Medicine (g) Recognition of pattern injuries in domestic violence victims. Computer Crime. Credit Cards: Forgery and Fraud. Crime-Scene Investigation and Examination (a) Recording. Crime-Scene Investigation and Examination (b) Collection and chain of evidence. Crime-Scene Investigation and Examination (c) Recovery. Crime-Scene Investigation and Examination (d) Packaging. Crime-Scene Investigation and Examination (e) Preservation. Crime-Scene Investigation and Examination (f) Contamination. Crime-Scene Investigation and Examination (g) Fingerprints. Crime-Scene Investigation and Examination (h) Suspicious deaths. Crime-Scene Investigation and Examination (i) Major incident scene management. Crime-Scene Investigation and Examination (j) Serial and series crimes. Crime-Scene Investigation and Examination (k) Scene analysis/reconstruction. Crime-Scene Investigation and Examination (l) Criminal analysis. Crime-Scene Investigation and Examination (m) Decomposing and skeletonized cases. Criminal Profiling. Criminalistics. Detection of Deception. Disaster Victim Identification. DNA (a) Basic principles. DNA (b) RFLP. DNA (c) PCR. DNA (d) PCR-STR. DNA (e) Future analytical techniques. DNA (f) Paternity testing. DNA (g) Significance. DNA (h) Mitochondrial. Document Analysis (a) Handwriting. Document Analysis (b) Analytical methods. Document Analysis (c) Forgery and counterfeits. Document Analysis (d) Ink analysis. Document Analysis (e) Printer types. Document Analysis (f) Document dating. Drugs of Abuse (a) Blood. Drugs of Abuse (b) Body fluids. Drugs of Abuse (c) Ante-mortem. Drugs of Abuse (d) Postmortem. Drugs of Abuse (e) Drugs and driving. Drugs of Abuse (f) Urine. Drugs of Abuse (g) Hair. Drugs of Abuse (h) Methods of analysis. Drugs of Abuse (i) Designer drugs. Dust. Ear Prints. Education, An International Perspective. Electronic Communication and Information. Entomology. Ethics. Evidence (a) Classification of evidence. Evidence (b)The philosophy of sequential analysis. Evidence (c) Statistical interpretation of evidence/Bayesian analysis. Expert Witnesses, Qualifications and Testimony. Explosives, Methods of Analysis. Facial Identification (a) The lineup, mugshot search and composite. Facial Identification (b) Photo image identification. Facial Identification (c) Computerized facial reconstruction. Facial Identification (d) Skull-photo superimposition. Facial Identification (e) http://www.elsevier.com/wps/find/bookdescription.cws_home/673576/description#descri... 06/03/2005 Elsevier.com Página 3 de 4 Facial tissue thickness in facial reconstruction. Fibres (a) Types. Fibres (b) Transfer and persistence. Fibres (c) Recovery. Fibres (d) Identification and comparison. Fibres (e) Significance. Fingerprints (Dactyloscopy) (a) Visualisation. Fingerprints (Dactyloscopy) (b) Sequential treatment and enhancement. Fingerprints (Dactyloscopy) (c) Identification and classification. Fingerprints (Dactyloscopy) (d) Standards of proof. Fingerprints (Dactyloscopy) (e) Chemistry of print residue. Fire Investigation (a) Types of fire. Fire Investigation (b) Physics/Thermodynamics. Fire Investigation (c) Chemistry of fire. Fire Investigation (d) The fire scene. Fire Investigation (e) Evidence recovery. Fire Investigation (f) Fire scene patterns. Fire Investigation (g) The laboratory. Firearms (a) Types of weapons and ammunitions. Firearms (b) Range and penetration. Firearms (c) CS Gas. Firearms (df) Humane killing tools. Firearms (e) Laboratory analysis. Forensic Anthropology. Forensic Engineering. Forensic Nursing. Forensic Psycholinguistics. Forensic Toxicology (a) Overview. Forensic Toxicology (b) Methods of analysis - ante-mortem. Forensic Toxicology (c) Methods of analysis - post-mortem. Forensic Toxicology (d) Interpretation of results. Forensic Toxicology (e) Inhalants. Forensic Toxicology (f) Equine drug testing. Forgery and Fraud (a) Overview (including counterfeit currency). Forgery and Fraud (b) Auditing and accountancy. Gas Chromatography, Methodology in Forensic Sciences. Genetics (a) Serology. Genetics (b) DNA - statistical probability. Glass. Hair (a) Background. Hair (b) Hair transfer, persistence and recovery. Hair (c) Identification of human and animal hair. Hair (d) Microscopic comparison. Hair (e) Other comparison methods. Hair (f) Significance of hair evidence. Hair (g) DNA typing. Health and Safety (including Risk Assessment). History (a) Crime scene sciences. History (b) Fingerprint sciences. Identification/Individualization, Overview and Meaning. Investigative Psychology. Legal Aspects of Forensic Science. Lie Detection (Polygraph). Literature and the Forensic Sciences (a) Resources. Literature and the Forensic Sciences (b) Fiction. Microchemistry. Modus Operandi. Odontology. Offender Signature. Paints and Coatings: Commercial, Domestic and Automotive. Pathology (a) Overview. Pathology (b) Victim recovery. Pathology (c) Autopsy. Pathology (d) Preservation of evidence. Pathology (e) Post-mortem changes. Pathology (f) Post-mortem interval. Pattern Evidence (a) Footmarks (footwear). Pattern Evidence (b) Footmarks (bare footprints). Pattern Evidence (c) Shotgun ammunition on a target. Pattern Evidence (d) Tools. Pattern Evidence (e) Plastic bag striations. Pattern Evidence (f) Serial number. Pharmacology. Post-Mortem Examination, Procedures and Standards. Psychological Autopsies. Psychology and Psychiatry (a) Overview. Psychology and Psychiatry (b) Psychiatry. Psychology and Psychiatry (c) Psychology. Quality Assurance/Control. Serial Killing. Soil and Geology. Stalking. Statistical Interpretation of Evidence. Time Factor Analysis. Voice Analysis. Wildlife. Wood Analysis. Bibliographic & ordering Information Hardbound, ISBN: 0-12-227215-3, 1440 pages, publication date: 2000 Imprint: ACADEMIC PRESS Price: Order form EUR 995 GBP 665 USD 995 Books and book related electronic products are priced in US dollars (USD), euro (EUR), and Great Britain Pounds (GBP). USD prices apply to the Americas and Asia Pacific. EUR prices apply in Europe and the Middle East. GBP prices apply to the UK and all other countries. Customers who order on-line from the Americas will be invoiced in USD and all other countries will be invoiced in GBP. See also information about conditions of sale & ordering procedures, and links to our regional sales offices. 999/999 http://www.elsevier.com/wps/find/bookdescription.cws_home/673576/description#descri... 06/03/2005 ACCIDENT INVESTIGATION/Airbag Related Injuries and Deaths 1 A ACCIDENT INVESTIGATION Contents Airbag Related Injuries and Deaths Determination of Cause: Overview Determination of Cause: Reconstruction Driver Versus Passenger in Motor Vehicle Collisions Motor Vehicle Rail Tachographs Airbag Related Injuries and Deaths W S Smock, University of Louisville, Louisville, KY, USA Copyright # 2000 Academic Press doi:10.1006/rwfs.2000.0748 Introduction During the past decade the motoring public has been shocked to learn that air bags, a life-saving device promoted by the automotive industry, can also induce severe and fatal injuries. Over the last 10 years in the United States, nearly 200 men, women and children have been fatally injured by deploying air bags. Thousands more have sustained serious nonfatal injuries, including cervical spine fractures, closed head injuries, and multiple fractures and amputations of digits and hands. Ironically, the vast majority of these serious and fatal injuries were incurred in low and moderate speed collisions in which little or no injury would have been otherwise expected. Historical Context The first air bag patents were filed in 1952. Ford and General Motors began experimenting with these early prototypes in the late 1950s. Based on documents from the automotive industry, it was apparent, even as early as 1962, that deploying air bags had the potential to induce serious and fatal injuries, particularly to children. These early documents include analyses of tests conducted by Ford at their automotive safety research office in the late 1960s. The tests demonstrated that there was sufficient force associated with air bag deployment to traumatically eject a child from a vehicle. Ford also noted the amputation of a steel-hinged arm from a dummy secondary to the explosive force of deployment. When testing involved the use of animal models, the list of severe and fatal injuries grew. Cardiac rupture, hepatic rupture, splenic rupture, aortic and vena cava transection, atlanto-occipital dislocation, cervical spine fractures, severe closed head injury and decapitation were observed. Testing in the 1980s by the automotive manufacturers continued to demonstrate the risk of injury induction. One study conducted and reported by General Motors indicated `many of the exposures were at loading severities beyond the level representing an estimate of nearly 100% risk of severe injury'. These laboratory tests were completed and the knowledge available to the entire automotive industry well before air bags were placed in Americanmade vehicles. With 40 years of research behind us and all of the resultant data before us, it is apparent that steering wheel and dash-mounted air bags, devices designed to protect occupants in high-speed frontal collisions, can also maim and kill. 2 ACCIDENT INVESTIGATION/Airbag Related Injuries and Deaths Automotive Industry During the period of 1960 to 1990, the automobile industry embraced an extensive research and development program regarding air bags. This testing involved anthropomorphic dummies, anesthetized swine and baboons, and even human volunteers. It was recognized early on that occupants in the path of the deploying air bag, or who were positioned close to the air bag at the moment of deployment, were at a very significant risk of receiving a severe or fatal injury. In January 1970, at a meeting of engineers from General Motors, Ford and Chrysler, this information was discussed. As a result, a Chrysler engineer wrote: `This is a very serious problem that must be resolved for the inflatable restraint. Having a child directly in front of the bag when it inflates could prove fatal.' General Motors tested air bags on baboons at Wayne State University during the early 1970s. The research indicated that `if the head is in the path of the deploying air bag, it is concluded that injury is likely to occur in the form of brain or neck injury to a child'. Testing by Ford in the 1970s revealed that individuals involved in collisions at less than 32 k.p.h. (20 m.p.h.) experienced more severe injuries and loading forces in vehicles equipped with an air bag than those without one. Ford also noted that there was `overwhelming evidence that air bags may be dangerous for small children'. In 1972, a Ford engineer wrote the following warning, which was never placed in a vehicle: `The right front seat should be used only by persons who are more than five feet [1.52 m] tall and are in sound health. Smaller persons and those who are aged or infirm, should be seated and belted in the rear seat.' In a series of tests conducted by General Motors in the 1980s, anesthetized swine were placed with their chests in close proximity to the air bag module. The tests revealed that when the swine's thorax was impacted by the force of the deploying air bag and the air bag module, significant thoracic and abdominal injuries were sustained. These injuries in one case included: 17 rib fractures; two cardiac perforations; a splenic laceration; a liver hematoma and death within 30 min. The proximity of the occupant to the deploying bag and module cover were the pivotal contributory factors. government and the automotive industry revealed that the majority of these victims were women of short stature. It was also noted that the fatal injuries could be incurred even if the occupant was restrained by a lap and chest belt. The injuries initially seen included massive head injuries with diffuse axonal injury, subdural hematomas and skull fractures. Additional injuries evaluated included cervical spine fracture, cardiac perforation, pulmonary contusions and multiple rib fractures. Sodium azide is the explosive propellant used to initiate the deployment cycle in most air bag designs in use today (Fig. 1). When sodium azide is ignited, the deploying air bag explodes toward the occupant at speeds of up to 336 k.p.h. (210 m.p.h.). An air bag system has two components, either one of which may induce injuries: the canvas-covered air bag itself and the air bag module cover (Fig. 2). Injuries incurred during deployment are relevant to the component inflicting them. Obviously, the types of injuries which result from impact with the canvas air bag are different from Figure 1 The air bag is transported as an explosive material. Sodium azide is the explosive propellant used in the majority of air bag modules. Human Injuries The serious and life-threatening injuries that were originally observed in the industry's laboratories using animal models began to be observed in humans on US roadways in the 1990s. The first six driver air bag-related deaths which were investigated by the Figure 2 The injury-producing components of the air bag system are the air bag and the module cover which overlies it. ACCIDENT INVESTIGATION/Airbag Related Injuries and Deaths 3 those which result from impact with its module cover. There are three phases to air bag deployment: `punch out', `catapult' and `bag slap'. Injuries can be inflicted at any point during the deployment process: . Punch out This is the initial stage of deployment. If the bag makes contact at this stage, the following injuries can result: atlanto-occipital dislocation, cervical spine fracture with brainstem transection, cardiac, liver and splenic lacerations, diffuse axonal injuries, subdural and epidural hematomas, and decapitation. . Catapult This is the midstage of deployment when rapidly inflating bag `catapults' or drives the head and neck rearward. This occurs with sufficient energy to rupture blood vessels, ligaments and fracture cervical vertebrae. The neck injuries occur as the result of cervical spine hyperextension. . Bag slap This is the final stage of deployment which occurs at the bag's peak excursion. Appropriately named, this happens when the canvas bag's fabric may `slap' the occupant's face, resulting in injuries to the eye and epithelium. The air bag module covers are located in the steering wheel on the driver's side and in the dashboard panel on the passenger side. As the bag deploys, the module cover is also propelled outward at speeds of up to 336 k.p.h. (210 m.p.h.). Most steering wheel designs house the horn within the air bag module compartment. Hand and arm injuries observed in individuals whose extremities were in contact with the module at the moment of its rupture include: degloving, fracture dislocation, fracture dislocation and amputations (partial and complete of digits and forearms). If the module cover makes contact with an occupant's face, head or neck, skull fractures and severe or fatal head injuries, and decapitations have also been observed. The driver's side cover is generally made with a rubberized plastic type of material, while the passenger side may have a metal housing. Contact with either type can prove fatal. Figure 3 (see color plate 1) This patient sustained a severe corneal abrasion secondary to the membrane forces associated with air bag deployment. Face and head The most common injury associated with air bag deployment is that of facial abrasion. The abrasions result from a sliding contact between the bag and the face (Fig. 4). The injuries are not chemical `burns' but deep abrasions. Specific Injury Patterns Ocular The eye is extremely vulnerable to air bag-induced injury. These injuries range from corneal abrasions from contact with the air bag, chemical burns from contact with unburned sodium azide, to retinal detachment and globe rupture from the blunt force trauma of the expanding bag (Fig. 3). The wearing of eyeglasses in some cases has proven to be of benefit, as it offers a degree of barrier protection between the eye and the deploying bag. Figure 4 Abrasions to the cheeks, forehead and nose are the most common injury associated with air bag deployment. 4 ACCIDENT INVESTIGATION/Airbag Related Injuries and Deaths Cranial and intracranial When acceleration forces are applied to the cranial vault, a variety of traumatic injuries to the brain and surrounding structures will result. These include subdural hematomas, cortical contusions, atlanto-occipital dislocations, skull fractures and brainstem transections. Cranial injuries may result from contact with either the deploying of bag or module cover (Fig. 5). Cervical spine The blow from an air bag or module cover which produces a rapid and violent hyperextension of the cervical spine of the driver or passenger will have significant consequences for the cervical vertebrae. Injuries commonly seen as a result of hyperextension include atlanto-occipital dislocation, comminuted fractures of one or more upper cervical vertebrae, rupture of the anterior and posterior longitudinal spinal ligaments, and cervical spine disarticulation with transection of the cervical cord. The majority of these injuries are associated with the upper cervical vertebrae, although lower cervical vertebrae injuries have been observed. Extremities The upper extremities are very vulnerable to traumatic injury from the deploying bag and its module cover. When an individual's hand or forearm is on or near the module cover at the moment of deployment, the occupant can expect to sustain multiple fractures, and/or tissue degloving or amputation of fingers, hand or forearm (Fig. 6). The horn-button-withinthe-module cover design significantly increases the risk of injury to the occupant's upper extremities at the moment of deployment. Many of these upper extremity injuries are associated with an occupant's attempt to blow the horn, the button of which is located within the module cover. Forces from air bag deployment may be transmitted to the hand, wrist or forearm and may even involve the humerus. It is not unusual to see significantly comminuted fractures involving the wrist, forearm, elbow and distal humerus (Figs 7 and 8). The vehicles whose module Figure 5 Cranial or facial contact with the deploying bag or Figure 6 When the forearm is located in a horizontal fashion A B Figure 7 When the hand, wrist or forearm is on or near the module cover at the moment of deployment, for example when blowing the horn, significant fractures, degloving injuries and amputations will result. (A) This open-comminuted bending fracture of the radius and ulna was the result of contact with the module cover. (B) This patient sustained a comminuted fracture of the proximal and midshaft ulna as well as a radial head dislocation from impact with the module cover. ACCIDENT INVESTIGATION/Airbag Related Injuries and Deaths A 5 B Figure 8(A) and (B) These severely comminuted fractures resulted when this individual was blowing her horn. She sustained a frontal impact of approximately 15 k.p.h., which resulted in air bag activation. The horn activation button was located within the module cover, which explains why the patient had her forearms over the module cover at the moment of deployment. covers are of a higher mass have the propensity to inflict more severe injuries. Some of the worst offenders are module covers located on the passenger side, which may have a soft coating of plastic on the exterior but have an underlying piece of rigid metal (Fig. 9B). The placement of hands on the passengerside dashboard, in a bracing maneuver, has resulted in the traumatic amputation of hands and forearms (Fig. 9A). ducts may also cause a chemical irritation of open wounds and a basic (high pH) burn to the eyes. Sample Cases Case 1 The byproducts of combustion as well as other inert materials within the air bag may produce a white cloud within the vehicle. Many occupants have thought that this indicated a vehicle fire. This whitish material is principally cornstarch, talc and the byproducts of sodium azide combustion. There may be a small percentage of unburned sodium azide present within this powder as well. Inhalation of these materials can result in a chemical pneumonitis and the induction of asthma-type symptoms. These bypro- A 35-year-old female, 1.57 m (5' 2'') and 50 kg (110 lb.), was the restrained driver in a 1991 Ford Taurus (Fig. 10). The vehicle's front bumper grazed a guard rail, which resulted in deployment of the driver's air bag. The patient sustained an immediate respiratory arrest, with subsequent declaration of brain death 12 h later. A postmortem examination was conducted and revealed the following injuries: significant midface trauma with bilateral epistaxis; corneal abrasions; contusions of the chest; left subdural hematoma (overlying the frontal and parietal regions); subarachnoid hemorrhage and severe cerebral edema. Examination of the exterior of the vehicle revealed very minor damage which was limited to the front A B Respiratory Figure 9 (A) This partially-amputated wrist was the result of placement of the front seat passenger's hand on the dashboard at the moment of deployment. (B) The underlying structure of the module cover was metal. 6 ACCIDENT INVESTIGATION/Airbag Related Injuries and Deaths A B Figure 10(A) and (B) A 1991 Ford Taurus was involved in a very minor glancing collision between the front bumper and a guardrail. There was no underlying frame, fender or structural damage. bumper. The examination of the interior revealed a tear on the left lower portion of the module cover (Fig. 11). This tear was the result of contact between the left side of the victim's face and the deploying module (Figs 5 and 11). Case 2 A 4-year-old male was the lap belt-restrained occupant of the front right seat of a 1995 GEO Metro (Fig. 12). The shoulder portion of the harness was placed underneath the right arm. The patient was catapulted from the front passenger seat to the rear of the vehicle. The patient was found pulseless and apneic on arrival of emergency medical services. A postmortem examination was conducted and revealed the following injuries: an atlanto-occipital dislocation with brainstem transection; large subdural hemorrhages; multiple rib fractures with underlying pulmonary contusions; liver and splenic lacerations; clavicular fracture and significant facial abrasions underlying the mandible bilaterally and on the right cheek (Fig. 13A). Examination of the abdo- A men also revealed a lap belt contusion below the umbilicus (Fig. 13B). Examination of the vehicle revealed front end damage consistent with a change of velocity of less than 15 k.p.h. (9 m.p.h.). There was no damage to the driver or passenger compartments. Examination of the passenger bag revealed the presence of blood and tissue transfer. The patient's injuries resulted from blunt force trauma to the chest and abdomen as well as a hyperextension injury of the neck with a rapid rearward acceleration. Case 3 A 35-year-old female was the front seat passenger in a 1995 Nissan Altima. The patient was in a lap± shoulder belt, with the passenger seat in the most rearward position. The vehicle was stopped in a line of traffic, waiting for a traffic signal to turn, when it was hit from behind by a vehicle travelling at the speed of approximately 5 k.p.h. (3 m.p.h.). The rear impact pushed the Nissan forward into the trailer hitch of the truck in front. This resulted in air bag B Figure 11 (A) The left lower corner of the module cover exhibited tearing from contact with the left side of the driver's face. (B) Close-up of the module cover reveals the presence of a torn area. There is also an area which indicates this piece was removed by a sharp implement. ACCIDENT INVESTIGATION/Airbag Related Injuries and Deaths A 7 B Figure 12 (A) and (B) A 1995 GEO Metro with minor front-end damage consistent with an impact speed of less than 15 k.p.h. (9 m.p.h.). deployment. The air bag impacted the patient's left eye. Examination of the face revealed significant periorbital trauma. There were abrasions on the forehead as well as on the cheek and chin. Examination of the eye revealed the presence of chemosis, a hyphema and a retinal detachment (Fig. 14). Examination of the vehicle revealed a 5 6 5 cm dent in the right front bumper (Fig. 15). There was no A B Figure 13 (A) This fatally injured 4-year-old male exhibits significant facial abrasion, overlying the mandible as well as abrasion on the left cheek. This was the result from contacts with the upwardly-deploying air bag. (B) Examination of the patient's abdomen reveals a horizontally-oriented contusion consistent with a lap belt. Figure 14 This 1.72 m (5' 8'') restrained patient suffered permanent retinal detachment secondary to air bag contact. 8 ACCIDENT INVESTIGATION/Airbag Related Injuries and Deaths A B Figure 15(A) and (B) A 1995 Nissan Altima. The only damage to the vehicle is a 5 6 5 cm indentation in the front bumper from impact with the ball of a trailer hitch. significant rear end damage. Examination of the bag revealed transfer of make-up and blood to the bag. Forensics of Air Bag Injuries Locard's principle regarding the transfer of physical evidence between two impacting objects is dramatically evidenced in the case of air bags and air baginduced injuries. The transfer of evidence to the air bag itself may take various forms. Blood and epithelial tissue transfer is, of course, common but transfer of make-up, including lipstick, rouge and mascara, to the air bag is also seen (Fig. 16). Analysis of the blood spatter pattern on the bag may assist the investigator in determining the position of the occupant and the configuration of the steering wheel at the moment of air bag deployment. Examination of the air bag module cover may reveal the presence of trace evidence. Depending on the design of the module cover, there may actually be tearing or bending of the module cover, indicative of contact with an occupant's more rigid (bony) surface: face or forearm. Scuff-type marks on the module cover indicate contact with an object, frequently the forearm (Fig. 17). Fabric imprints may also be seen on close inspection (Table 1). Summary In the United States the deploying air bag has been responsible for nearly 200 deaths and thousands of Figure 17 Close inspection of a module cover may reveal the presence of scuffing, and fabric imprints. Table 1 Trace evidence. Air bag Blood Make-up Hair Tissue Figure 16 Close examination of an air bag may reveal a multitude of transferred evidence. This evidence will include: hair, blood, epithelial tissue and facial makeup. Module cover Tearing of cover material Scuff marking Fabric imprint Tissue Hair ACCIDENT INVESTIGATION/Determination of Cause: Overview severe injuries. It is clear that the forces of deployment are not insignificant and must be respected by the vehicle occupant. A review of the literature indicates that the serious and fatal injuries, which were once produced in the laboratory setting, are now being observed in `real-world' collisions. Many clinicians may not be aware of the injury-producing power of the deploying air bag and must be informed of the patterns associated with air bag-induced injuries. The motoring public must also be informed and warned of the dangers of air bag deployment, just as the automotive industry was over 30 years ago. See also: Accident Investigation: Motor Vehicle. Further Reading Horsch J, Lau I and Andrzegkad et al. (1990) Assessment of Air Bag Deployment Loads, SAE 902324. Detroit: Society of Automotive Engineers. Huelke DF, Moore JL, Compton TW et al. (1994) Upper Extremity Injuries Related to Air Bag Deployments, SAE 940716. Detroit: Society of Automotive Engineers. Huelke DF, Moore JL and Ostrom M (1992) Air bag injuries and accident protection. Journal of Trauma 33:894±897. Landcaster GI, Defrance JH and Borrusso J (1993) Air bag associated rupture of the right atrium. New England Journal of Medicine 328:358. Lau I, Horsch JD, Viano DC et al. (1993) Mechanism of injury from air bag deployment loads. Accident Analysis and Prevention 25:29. Mertz HJ and Weber DA (1982) Interpretations of Impact Response to a Three Year Old Child Dummy Relative to Child Injury Potential, SAE 826048. Detroit: Society of Automotive Engineers. Mertz HJ, Driscoll GP, Lennox JB et al. (1982) Response of animals exposed to deployment of various passenger and portable restraint system concepts for a variety of collision severities and animal positions. National Highway and Transportation Safety Administration. 9th International Technical Conference on Experimental Safety Vehicles, pp. 352±368. Kyoto, Japan, November 1982. Parents for Safer Air Bags (1997) The Air Bag Crisis: Causes and Solutions. Prasad P and Daniel RP (1984) A Biomechanical Analysis of Head, Neck and Torso Injuries to Child Surrogates Due to Sudden Torso Acceleration. SAE 841656. Detroit: Society of Automotive Engineers. Smock WS (1992) Traumatic avulsion of the first digit, secondary to air bag deployment. Proceedings 36. Association for the Advancement of Automotive Medicine, p. 444. Des Plains, IL. Smock WS and Nichols GN (1995) Air bag module cover injures. Journal of Trauma, Injury, Infection and Critical Care 38:489±493. Viano DC and Warner CV (1976) Thoracic Impact Response of Live Porcine Subjects, CvSAE 760823, 733±765. Detroit: Society for Automotive Engineers. 9 Determination of Cause: Overview D Rudram, The Forensic Science Service, London, UK Copyright # 2000 Academic Press doi:10.1006/rwfs.2000.0398 Introduction The purpose of all accident investigation is to establish the `cause' of the incident. This information will be sought for a number of reasons which may overlap. Thus the victims or their family will want to know why they were injured or killed, regulatory authorities may wish to establish responsibility and take appropriate action as a result and safety authorities will want to see what can be done to prevent a re-occurrence. What do we mean by the cause of an accident and if it was caused by the actions or omissions of someone is it really an accident at all? The term `dangerous occurrence' used in Health and Safety Regulations is in many ways more appropriate but the neutral term `incident' will be used here. There can be several causes for one of these dangerous occurrences and the causes are often multilayered; the investigator needs to keep this firmly in mind when analyzing the data and reaching a conclusion. As always the investigator needs to have a clear understanding of the available evidence and what it means. An example from some years ago illustrates both of these points. In 1975 a train on the London Underground ran into the blank wall at the end of the line at Moorgate Station. The immediate cause of the incident was the failure of the train to stop at the final station which was brought about because the driver did not obey the signals which controlled the speed of approach of the train. But why did the driver ignore these signals? There was alcohol in both the driver's blood and the drink that he had with him when they were analyzed post mortem. An explanation for his actions perhaps? The driver, however, was an abstemious man and the incident happened early in the morning rush hour so, although not impossible, alcohol seemed an implausible explanation. Also as the incident occurred underground, the driver's body was not recovered for several days and the temperature in the tunnel was elevated, the conclusion that postmortem putrefaction rather than antemortem drinking was the explanation for the presence of alcohol becomes more likely. This incident illustrates that sometimes the ultimate cause of a dangerous occurrence is never known. 10 ACCIDENT INVESTIGATION/Determination of Cause: Overview Sources of information Establishing the sequence of events which led up to an incident is usually an essential prerequisite for establishing why the incident happened. To do so successfully the investigator needs information and usually the more information the better. Although this can lead to problems of assimilation, arbitrarily excluding some sources or types of information runs the risk of excluding the vital fact which enables an investigator to unravel the puzzle. Information can be obtained from many sources each with its own advantages and disadvantages all of which need to play a part in the interpretation of events. Eye witnesses The evidence of witnesses needs to be treated with great care. People can genuinely believe they saw something which was impossible but this should not cause the investigator to dismiss them out of hand. Some of their observations may be crucial. An eye witness can provide information that is available from no other source. For example: . Did the pedestrian walk quickly or slowly? . Did they cross the road in a straight line? . What color were the traffic signals? Questions that the investigator should be asking about this evidence should include: . Where was the witness and what could he or she see from there? . Is their evidence supported by another witness or other information? . Are the stories of two witnesses too similar, suggesting that they have colluded, albeit innocently? Finally it should be remembered that some research suggests that certainty is no guarantee of accuracy of recall. Tire and other marks in the road One of the most common sources of information in the investigation of road traffic incidents are tire marks, scrapes and gouges left by the vehicles in the road before, during and after the impact. These marks can provide both qualitative and quantitative information about the incident. The position and orientation of tire marks indicate the path of the vehicles before and after the incident and changes in the direction of tire marks, gouges and scrapes in the road surface can indicate the position of the vehicle at impact (Fig. 1). The nature and dimensions of the tire marks may enable the investigator to calculate the speed of one or more of the vehicles which is usually an essential component of any analysis of the cause of the incident. Figure 1 Tire marks scrapes and gouges can be seen in the roadway following this incident involving two goods vehicles. # Metropolitan Police Service. The investigator needs to understand how the marks were made and as a consequence what that tells them about the incident. Speed estimates are an important component in any analysis of road traffic incidents but care needs to be used in interpreting them. The accident investigator needs to consider how precise is the estimate and at what point in the developing situation was the vehicle traveling at that speed. Vehicle damage The damage sustained by the vehicles also provides both qualitative and quantitative information. The nature and position of the damage will indicate the direction of the applied force from which the relative movements of the vehicle or vehicles can be deduced (Fig. 2). If one of the vehicles is stationary the problem is simplified considerably. The extent of the damage can be used to calculate the velocity change caused by the impact. Damage alone does not enable the impact speed to be calculated without some additional information. Again impact with a stationary object is the simplest case to deal with but in other circumstances the post impact movements of the vehicles need to be considered. It is very easy to misinterpret vehicle damage and the investigator needs to understand the limitations of the model that is being used. The angle of impact can have a significant effect on the answer and care needs to be taken in assessing this. The location and direction of the applied force both affect the precision of the calculation and the investigator needs to understand these effects and interpret the results accordingly. Although reasonably reliable results can be obtained for a collision involving two cars, big differ- ACCIDENT INVESTIGATION/Determination of Cause: Overview 11 the vehicle it provides a means of assessing the reliability of other estimates. Finally the nature and location of the damage to the vehicle also provides an indication of the impact speed. None of these methods on their own provide the level of certainty that can be obtained from impacts between two vehicles but in combination they can give a clear indication of likely speed and provide a useful check on other data sources. Vehicle condition Figure 2 The relative position of this car and the one that struck it can be deduced from the damage to the front. # Metropolitan Police Service. ences in the weights of the vehicles can cause unacceptably large errors particularly for the lighter one. This error is proportional to the mass ratio of the vehicles and if this exceeds 2:1 calculated values should be treated with circumspection. Although a very high proportion of road traffic incidents are caused by road users, defective vehicles do contribute to these incidents. The defects can be caused by poor maintenance, prior damage or modifications which are ill conceived and/or poorly executed. An important part of any investigation is the elimination of potential causes and a careful examination of the vehicles involved for defects which might have contributed to the incident should always form a part of the inquiry. This examination is complicated by vehicle damage which coincides with the apparently defective component. This is not always a coincidence as more often than not the failure of the component is a consequence and not a cause of the incident. Pedestrian impacts Photographs and plans Interpreting the results of impacts between pedestrians and cars is particularly difficult and precise estimates of impact speed cannot be made. A variety of techniques are available which provide some guide to the speed of a car which strikes a pedestrian. When the pedestrian is struck by the front of the vehicle empirical relationships between the distance the pedestrian was thrown and the impact speed have been deduced (Fig. 3). Secondly, there is also a statistical correlation between impact speed and the severity of the pedestrian's injuries. Although this cannot provide unequivocal information about the speed of Photographs and plans are an invaluable source for the investigator and one is not a substitute for the other. If the investigator did not visit the scene, photographs provide a source of information which supplements and amplifies that obtained from witnesses and provide an indispensable aide memoire in other cases. It is not unknown for tire marks which could not be seen clearly at the scene to show up in photographs. However, photographs can distort as well as enhance perceptions. Camera angle and the lens used may distort perspective and liberal use of a flash gun will make the scene appear brighter than it really was. Plans are only as good as the survey from which they were drawn. However, they should show the relationship between the vehicles, victims, marks and ephemeral evidence and the important features of the scene accurately. They can be used to derive measurements which were not taken at the scene although all important measurements should have been recorded directly at the scene. The relationship between the scale of the plan and the error in such derived values needs to be borne in mind. Rectification programs are now available which allow information to be extracted from photographs and complete plans constructed or missing detail added to existing plans. Figure 3 Pedestrian throw distance. 12 ACCIDENT INVESTIGATION/Determination of Cause: Overview Accurate plans are an essential starting point for any simulation program. Accurate records that can be understood by a layman will be important in any subsequent court proceedings. Accuracy will help to insure that records made by other personnel correspond with the plans. Speed Why calculate speed Why does estimating vehicle speed figure so predominantly in road traffic incident investigation? There are two primary reasons for this. First, speed itself can cause the crash. A good example of this is loss of control when cornering. Such accidents are usually caused by traveling too fast for one or all of these reasons: . the ability of the driver; . the performance of the vehicle; . the condition of the road. This is most clearly seen and most easily dealt with when the car leaves the curved striated tire scuff marks characteristic of a vehicle cornering at the limits of adhesion. The other principal reason for wanting an estimate of speed is to use it as a factor in the analysis of the incident. In any collision involving two moving objects the analysis needs to consider their relative movements and intervisibility which requires some knowledge of their velocity. Vehicle speed There are many ways in which the speed of a vehicle can be estimated. These include: . the length of skidmarks; . the radius of curved scuffmarks; . vehicle damage. Skidmarks Skidmarks are left by wheels which are no longer rotating. The marks are characteristic in appearance (Fig. 4) and caused as the wheels slide across the surface of the road. If all the wheels of the vehicle have locked then it is only friction between the tires and the road surface that is slowing the vehicle down. Although a great variety of tires are available those designed for road-going cars are all subject to the same design constraints. As a consequence, the major variables which determine the distance a car takes to skid to a halt are speed and the nature of the road surface. Thus if the coefficient of friction (m) between tires and the road surface can be measured Figure 4 This car left two clearly defined skid marks which deviate sharply to the left part way along. This indicates the point of impact with the victim. # Metropolitan Police Service then a reliable estimate of the speed (v) can be calculated from the length of the tire marks (s). If a car is skidded to a halt from a known speed then: v2 =2gs where g is the acceleration due to gravity and then the speed of the car leaving the skidmarks is given by: p v 2gs Curved scuffmarks The cornering force required to enable a car to follow a curved path is generated by friction between the tires and the road surface. Consequently tire/road friction sets an upper limit on the cornering force which can be generated and hence the speed at which any particular curved path can be followed. If this maximum speed is exceeded then the car side slips and leaves characteristic tire marks. These marks are curved and have a pattern of diagonal striations across them (Fig. 5). The rear wheel on the outside of the curve also tracks outside the front wheel. Once a car starts to leave these scuffmarks the driver has lost control. Experimental evidence shows that once this point is reached the difference in handling between different vehicles has no effect on the radius of the first part of the scuffmarks which are left. These differences may, however, affect the driver's ability to regain control of his or her vehicle. The significant variables are the coefficient of friction and the radius of the tire marks. ACCIDENT INVESTIGATION/Determination of Cause: Overview 13 Figure 5 A vehicle cornering at the limits of adhesion leaves characteristic striated scuff marks which show clearly on the white line in this photograph. # Metropolitan Police Service. If these are known, the speed of the car can be estimated with a precision of about +10%. The radius (r) of the initial section of the scuffmark can be obtained by simple geometric methods and then: p v gr Vehicle damage At a very simple level there is no surprise in the observation that the faster a car is traveling when it hits something the greater the damage. The observation that the extent of the damage to vehicles of similar size in similar impacts is comparable is perhaps rather more unexpected. The explanation is relatively simple, the manufacturers all have to face the same design constraints and type approval testing. This provides another useful tool for determining the speed of vehicles in road traffic incidents. Vehicle damage alone will not enable the impact speed of a car to be calculated as the extent of the damage depends on the change in speed (Dv) brought about by the collision. Thus a car brought to a halt by colliding with a wall at 30 mph will receive the same damage as a car colliding with another, stationary, car of similar mass at 60 mph where the post impact speed of both vehicles will be 30 mph. In all three cases Dv is 30 mph. Although it is possible to calculate Dv by hand most of this work is done using computer programs. The data supplied to the program must be accurate and like all computer models the user must understand the limitations. In knowledgeable hands these programs can give accurate and reliable estimates of Dv which, coupled with knowledge of the post impact behavior of the car(s), can provide an estimated impact speed. pedestrian's speed of movement will be required. This can be arrived at in a number of ways. An upper limit on how fast a pedestrian could possibly be moving can be deduced from the world record for the 100 m race. As this is just under 10 s no ordinary pedestrian is likely to run at more than 10 m s71. Of more direct relevance the rule of thumb (Naismith's Rule) used by hill walkers to calculate point to point times is based on a walking speed of 3 miles or 5 km h71 ± equivalent to 1.4 m s71 ± on the level. This is probably a good starting point for any calculations based on a pedestrian's walking speed. An alternative approach is to look up previously recorded figures for pedestrian speed. These may provide information about the affects of age, injury and disability on walking speed but some effort will be required to interpret the information given. Finally the speed at which people similar to the victim move can be measured. This can be tackled in a number of ways. For example covert observation of the pedestrian crossing where the incident occurred will enable an investigator to measure the time taken by people similar to the victim to cross the road. An alternative, particularly where a child running was involved, is to get a number of children of the same age and stature as the victim to run over the same distance and to time them. This should be treated as a game if possible and is best done in consultation with the adult responsible for the children. Although asking the victim to repeat his or her movements has obvious appeal it should be remembered that the victim is not an independent observer of events. Pedestrian speed Time and Distance If the conflict which led to the incident being investigated involved a pedestrian some estimate of the In many cases the reason for determining the speed of both vehicles and pedestrians is to analyze the 14 ACCIDENT INVESTIGATION/Determination of Cause: Overview movements of the two objects which collided. Such analysis will show where the car might have been when the pedestrian stepped from the kerb or where the vehicle in the main road was when the other vehicle pulled out from the side turning. Comparison of the impact speed of an emerging vehicle with the distance traveled from a stop line to impact may enable the investigator to draw conclusions as to whether or not this vehicle complied with the stop sign. Two other factors, visibility and reaction time, play an important part in assessing the relative movements of vehicles and pedestrians. Without some knowledge of these it is impossible to draw conclusions from the relative movements of the parties to the incident. Visibility Before a driver or pedestrian can react to the presence of someone else they have to be able to see them. Although measuring visibility is not difficult it needs to be done with some thought. For example the visibility for one party may not be the same as that for the other. Take the example of a car waiting to emerge from a side turning where visibility is restricted by a fence. If the car has a long bonnet the driver will be some distance behind the give-way or stop line and thus the driver of the oncoming vehicle will be able to see the waiting car before the waiting driver can see the approaching vehicle (Fig. 6). The height of the vehicle and the driving position and even the height of the pedestrian can have a significant effect on visibility. Thus when measuring visibility the observer should have his or her eyes at the same height as the witness and should be in the same lateral position in the road. As far as possible Figure 6 Visibility may not be the same for both vehicles involved in an incident. Top: car A is able to see car B from some distance before it reaches the `Give Way' sign. Bottom: Even at the stop line car B cannot see car A until it is much closer. the target should be as similar as possible to the actual target in the incident. Reaction time A ball rolls into the road with a child in hot pursuit. This is a clearly identifiable hazard but there is an appreciable delay before the approaching car begins to brake. Why was there a delay between the hazard appearing and the driver's response? Human beings cannot react instantly because a number of cognitive processes have to take place first. . Perception of the child approaching or entering the carriageway; . Recognition that a hazard has appeared; . Decision as to whether to brake or steer; . Action to apply the brakes. For most drivers the time taken to complete the last two stages will be very short. In the context of the investigation of dangerous occurrences on the road, however, it is the delay in seeing and recognizing the hazard which gives rise to arguments. This delay between the hazard appearing and action commencing is called reaction or perception±response time. Although defining reaction time is a necessary preliminary to measuring it, actual measurement is difficult. Most systems designed to measure reaction time modify the value being measured by warning the driver to expect something and telling him or her what action to take. Many tests bear little resemblance to real driving conditions. The most widely known estimate of reaction time in the UK is that used to derive the thinking distance component of stopping distance in the UK's Highway Code. The origin of this figure, 0.68 s, is lost in the mists of time but it is probably significant that it amounts to 1 foot of thinking distance for every mile per hour of speed. It is unrealistically short for normal drivers in real driving conditions. It is difficult to set up an experiment which measures driver reaction time without having to tell the driver what is happening. One attempt to do so used a driving simulator for what were ostensibly tests quite unconnected to reaction time. Eleven drivers were tested who fell into two groups with mean reaction times of 0.83 s and 1.13 s. The slowest driver took 1.43 s. Alcohol and some other drugs tend to extend a driver's reaction time, often quite significantly. Perception±response time is discussed at some length in the literature. Although driver reaction time is a complex problem in cognitive psychology, investigation of road traffic incidents requires an understanding of the concept and the range of values which the normally ACCIDENT INVESTIGATION/Determination of Cause: Overview 15 alert driver might achieve. The effect of expectation on response should not be overlooked. Drivers do not expect pedestrians to be crossing multi-lane dual carriageways and thus react slowly when they do. The eye witnesses The evidence of eye witnesses needs to reviewed carefully. However, with care they can provide reliable evidence which can be obtained in no other way. The investigator needs to consider the following. Interpretation . What do they say and are they consistent? . If, as is normal, they disagree are there any areas of agreement? . Are there obvious explanations for disagreements (e.g. their viewpoint)? . Is there information which will be required for subsequent analysis? e.g. the state of traffic signals; the direction of travel and speed of pedestrians and vehicles. General considerations The critical part of any investigation is the collation and interpretation of the information obtained. This should be tackled in a logical and methodical manner and will be an iterative process which should have started as the information is collected. A growing understanding of the incident will have directed the investigator's inquiry to insure that the right information is obtained and nothing is overlooked. Care must be taken not to exclude alternative plausible explanations until sufficient information has been collected to justify ignoring them. All evidence particularly that of eye witnesses should be considered critically. . . . . Could the witness see? What attracted the witness's attention? Are the plans accurate? Do the photographs give the correct impression with no distortion of perspective. . Is what the witness saw possible? . What is the precision of the calculations and how in consequence should they be interpreted? Analysis of the information will go through a number of overlapping stages. Information obtained from one stage may well modify that obtained from an earlier stage which will need to be re-assessed. By the end of this iterative process the investigator will have firm factual and logical foundation for his or her conclusions. Analytical process There is no one correct way of analyzing an incident but all of the following steps should be included. Plans, photographs and observations Good plans and photographs enable the investigator to get a clear picture of the scene, an essential first step in the analysis of the incident. Plans and photographs: . provide a vital aid to understanding what the witnesses are saying; . show the relationship between marks, participants and the environment; . allow the investigator to develop his her own interpretation of events; . may be used as a source of data. Skidmarks and scuffmarks Ephemeral evidence left at the scene is one of the basic building blocks of a successful reconstruction of a road traffic incident. . What marks have been left on the road surface? . What can be deduced about the movements of vehicles and pedestrians from them? . Can they be used to estimate speed? The vehicle(s) The condition of the vehicle(s) involved in the incident is important for two reasons. . Is the vehicle itself a cause of the incident? . Can anything be deduced about impact speed? Calculations Calculations based on observations and measurements are inevitably multistage processes which may involve re-evaluation of the other information between stages: . Estimate of vehicle speed from tire marks, damage etc. . Estimate time taken for: . the pedestrian to cross the road; . another vehicle to emerge from a side road; . a vehicle to skid to impact. . Investigate questions of intervisibility or reaction time. With all calculations the investigator needs to be aware of: . the accuracy and precision of the result; . the sensitivity of the result to changes in input information. At each stage other information should be reevaluated and the direction of the investigation reviewed. What should be done and in what order will depend on the circumstances, but at the end of one or more iterations the investigator should have a clear understanding of the incident and how it 16 ACCIDENT INVESTIGATION/Determination of Cause: Reconstruction developed and be in a position to explain it in clear, simple language. Conclusion Throughout any analysis of an incident the investigator should always search for ways of corroborating one source of information with another. At the end of the process the explanation of the sequence of events leading up to and through the incident should be internally consistent and include all the known data. If some data have been excluded the investigator should provide reasons ± no data should just be ignored. Finally, the investigator must report his or her findings clearly and simply setting out the information available, logical process gone through, and the conclusions reached. Just as photographs, plans and other illustrations can assist the investigator to understand what happened they can be used to support and amplify the report. The old adage that a picture is worth a thousand words remains true. The primary reason for investigating road traffic incidents is to learn what lessons they teach and thereby improve road safety. The investigator endeavors to establish what happened, why it happened and how repetition can be avoided. By learning from experience the UK has reduced annual road traffic fatalities from around 5600 to around 3600 in 13 years. Further significant reduction in this figure must be achieved and thorough, knowledgeable investigation of all incidents and application of the lessons learnt will continue to play a significant part in achieving this goal. See also: Accident Investigation: Motor Vehicle; Rail; Determination of Cause: Reconstruction; Tachographs; Driver Versus Passenger in Motor Vehicle Collisions. Pattern Evidence: Vehicle Tire Marks and Tire Track Measurement. Further Reading Allen M, Abrams B, Ginsberg A and Weintrub L (1996) Forensic Aspects of Vision and Highway Safety. Tucson, AZ: Lawyer's & Judge's Publishing. Backaitis SH (1989) Reconstruction of Motor Vehicle Accidents ± A Technical Compendium. Warrendale, PA: Society of Automotive Engineers. Backaitis SH (1990) Accident Reconstruction Technologies ± Pedestrians and Motorcycles in Automotive Collisions. Warrendale, PA: Society of Automotive Engineers. Baker JS and Fricke LB (1986) Traffic Accident Investigation Manual ± At Scene and Technical Follow Up. Evanston, IL: Traffic Institute, Northwestern University. Eubanks JJ (1994) Pedestrian Accident Reconstruction. Tucson, AZ: Lawyer's & Judge's Publishing. Fricke LB (1990) Traffic Accident Investigation Manual; vol. 2, Traffic Accident Reconstruction. Evanston, IL: Traffic Institute, Northwestern University. Noon RK (1994) Engineering Analysis of Vehicular Accidents. Boca Raton, FL: CRC Press. Obenski KS (1994) Motorcycle Accident Reconstruction ± Understanding Motorcycles. Tucson, AZ: Lawyer's & Judge's Publishing. Olsen PL (1996) Forensic Aspects of Driver Perception and Response. Tucson, AZ: Lawyer's & Judge's Publishing. Watts AJ, Atkinson DR and Hennessy CJ (1996) Low Speed Automobile Accidents. Tucson, AZ: Lawyer's & Judge's Publishing. Determination of Cause: Reconstruction H Steffan, Technical University Graz, Graz, Austria Copyright # 2000 Academic Press doi:10.1006/rwfs.2000.0395 Introduction Car traffic has increased dramatically. Although additional traffic regulations, such as speed limits, and other restrictions were imposed to reduce accidents, crashes can be seen every day. Many result in vehicle damage or injuries to occupants or others. Claims resulting from these accidents often have to be settled in court. In most countries special `accident experts' assist judges in reconstructing accident situations, based, for example, on information from eyewitnesses, car deformations or tire marks. In many countries these experts are either specially trained police officers or members of the road authorities. In others, reconstructions are performed by independent specialists. These accident analyses, which form the basis for court decisions, were the start of specific accident research. Accidents are also reconstructed for many other reasons. Car manufacturers perform in-depth studies of real accidents to learn more about accident mechanisms and to study the potential and the effectiveness of new safety devices in cars. Accidents are also often reconstructed and analyzed to help improve road planning. There are several questions that must be answered when reconstructing a car accident. Today's accident reconstruction tries to provide full information about the movement of all involved vehicles, persons or objects from the point of first visual contact to their ACCIDENT INVESTIGATION/Determination of Cause: Reconstruction rest positions. Time history of velocities, positions and crash-related data, such as velocity changes, deformation energies and passenger loads, must be analyzed. In addition, prevention analyses are often included. These analyses allow determination of the conditions necessary to prevent repetition of the accident. There is one general rule in any accident reconstruction: a detailed collection of scene data forms the basis for a good reconstruction. Some of the most important scene data are: . . . . vehicle or human rest positions; road marks; vehicle damages and marks; personal injuries. Owing to the increased number of cars with ABS, fewer tire marks, which formed the most objective basis, can be seen and thus one major contribution to the reconstruction is lost. On the other hand, the increased performance of personal computers has made it possible to use highly sophisticated reconstruction or simulation algorithms to study accidents. In recent years several software products have been developed for the reconstruction of vehicle accidents. Some of them are designed just to calculate vehicle velocities from the kinematics of specific accident types. Others, with full vehicle simulators, allow the simulation of car motion during the accident, starting from the point of reaction to the end position for any kind of accident. It is now even possible to visualize the car motion on the screen during the calculation in real time. Three-dimensional geometric information regarding road marks can be imported from CAD systems or from photographs as scanned bitmaps, and all important road, car and tire characteristics can be taken into account, as well as the reactions of the driver. Targets It is important, when formulating the physical and mathematical model of a car, to take into account the fact that many parameters are not well known when reconstructing the accident. In particular, the condition of the tires, such as their age or air pressure, the dampers or the steering system are often not well documented. The resistance of the chassis is only known for well-defined crash conditions and not for the specific accident situation. Therefore it is important to find a compromise between accuracy and the amount of input data necessary to perform the calculation. On the other hand, the user should be able to take into account all parameters which are documented and known to influence driving and crash behavior. Based on this knowledge, simplified models 17 have to be used, which guarantee that the basic driving behavior is predicted correctly. All necessary input parameters must be defined on the basis of physical parameters and a simple means of varying the parameters guarantees that the expert can crosscheck their influence on the simulation result. The automotive industry uses several simulation models to learn about the driving behavior of vehicles. These industrial vehicle dynamics simulation programs are optimized to predict driving behavior under well-defined initial and boundary conditions. As a result these models require many input parameters. For the reconstruction of a vehicle accident, such detailed knowledge, especially regarding the suspension, the tires and the road conditions, is normally not available. In addition, the steering and degree of braking are often not known. It is thus difficult to use these simulation models for the reconstruction of vehicle accidents. A similar problem exists regarding collision models. Several programs (mainly finite element (FE)based) exist that allow the calculation of the deformations for well-defined collision conditions. To achieve good agreement with real impacts, they require a very detailed knowledge of the vehicle structure and a very powerful computer. Some 100 000 degrees of freedom are required to model one vehicle properly. In addition, every simulation has to be calibrated with similar crash tests. This is the major reason why FE programs are only used for accident reconstruction in a few specific cases. Several computer programs have been developed especially for the reconstruction of vehicle accidents. They allow the calculation of vehicle motion and collisions based on various physical models. PCCRASH is one of these programs with a worldwide distribution. It uses a kinetic time forward simulation of vehicle dynamics and combines it with a momentum-based collision model; accidents can be reconstructed, starting from the point of reaction to the end position, for all involved cars simultaneously. The reconstruction is performed in an interactive graphical environment, which allows a sketch or photograph of the accident scene to underlay the reconstruction. For an effective presentation of the results, 3D animations can be created directly from the calculated results. Accident Analysis Postcrash movement In a conventional accident analysis the reconstruction is normally started from the rest positions of the involved vehicles and calculated backwards to the 18 ACCIDENT INVESTIGATION/Determination of Cause: Reconstruction collision position. To determine the postcrash velocity of the vehicles, an average deceleration has to be estimated. In many cases, where no tire marks are available, straight-line movement of the vehicle is assumed for determining the distance of postcrash travel. Depending on the road situation and involved vehicle, an average deceleration level is assumed, typically in the range of 0.1±10 m s72. The postcrash velocity can than be calculated according to the formula: q Equation 1 2as 02 where v represents the postcrash velocity (m s71), a the average deceleration (m s72) and s the postcrash travel of the vehicle's center of gravity (m). The major problem with this method is estimating the vehicle's average deceleration during a complicated postcrash movement. In this phase the vehicle may have been rolling or sliding and this has a huge influence on the amount of energy dissipated. To overcome this problem, vehicle simulators are often used to compare the vehicle's movement with marks found on the road or on the vehicle. Thus the postcrash velocity can be determined more accurately. Collision model During the collision the contact forces between the two involved vehicles vary over time. These forces depend on the vehicle structure, the deformation velocity, the contact situation and several other parameters. As these dependencies are highly nonlinear and very difficult to formulate, the treatment of the parameters through their integral values has proven to be more efficient. Modern FE programs allow investigation of the time variation of the contact forces. But these programs require enormous calculation times and a huge amount of modeling. Simplified models like the CRASH algorithm have produced large errors under several conditions. In many cases, insufficient knowledge regarding the structural deformation behavior is available to estimate the proper parameters. Crash hypotheses that only compare the velocity conditions of both vehicles before and after the impact have therefore been used with great success for the reconstruction of accidents. Material properties in the contact area During the contact phase large forces may occur, which cause deformations to one or both collision partners. These deformations may remain fully or partially after the impact (plastic deformations) or they may fully recover (elastic deformations). Through the defini- tion of the parameter k the amount of elasticity for a crash can be defined. This parameter k is only valid for a whole crash situation and not for one of the partners. Therefore one crash partner may exhibit a high degree of elasticity when impacting with partner A and a high degree of plasticity when impacting with partner B. Using an example of a straight central impact (Fig. 1), the parameter k can be easily explained. To insure that the two partners collide, the velocity of partner 1 must be higher than the velocity of partner 2. In phase 1 contact forces act, which reduce the velocity of mass 1 and increase that of mass 2. They are equivalent in size, but with opposite direction. The relation between acceleration and contact force is calculated from: ma F Equation 2 where m defines the mass, a the acceleration and F the contact force. The end of phase 1 is defined when both partners have equal velocities. It is called the `compression' phase. In phase 2 the forces reduce again until the two masses separate. This phase 2 is called `restitution'. In this case the coefficient of restitution is defined as k 2 0 2 1 0 1 Equation 3 05k51 where k=0 represents a fully plastic and k=1 a fully elastic impact. Eccentric impacts Figure 2 shows an example of a measurement of the two acceleration components for an eccentric impact. The compression moment Sc and restitution momentum SR are now defined as Z tm Fdt Equation 4 SC t0 Z SR t1 tm Fdt Equation 5 where t0 is the time of first contact, tm defines the time of identical velocity for both vehicles at the point of impact and t1 describes the time of separation. Figure 1 Central impact. See text for explanation. ACCIDENT INVESTIGATION/Determination of Cause: Reconstruction 19 where Vlt defines the velocity component of the impulse point for vehicle 1 in direction t and Vln in direction n. So the components of the relative velocity for both vehicles at the impulse point can be calculated from In the case of a generic eccentric impact, the `coefficient of restitution' is now defined as a ratio between restitution momentum and compression momentum SR SC V2t Equation 10 Vn V1n V2n Equation 11 In addition, the balance of momentum can be formulated for both vehicles Figure 2 Measured accelerations. " Vt V1t Equation 6 The total exchanged momentum is calculated from S SC SR SC 1 " In a full impact the velocities of both vehicles at the impulse point must be identical at the end of the compression phase (Fig. 3). For simplicity, the impact model is only derived here in 2D. In some programs like PC-CRASH the models are also extended to 3D. They are identical except that all velocities, the momentum and angular momentum are defined in 3D coordinates and all three components of the velocity and rotational velocity are taken into account. As can be seen in Fig. 3 a local coordinate system is defined, which originates at the `impulse point'. The components of the relative velocity for both vehicles at the impulse point can be calculated from: V1t vs1t !1z n1 Equation 8 V1n vs1n !1z t1 Equation 9 m1 v0s1t vs1t T Equation 12 m1 v0s1n vs1n N Equation 13 m2 v0s2t vs2t T Equation 14 m2 v0s2n vs2n N Equation 15 The balance of angular momentum can be formulated I1z !01z I2z !02z !1z Tn1 !2z Nt1 Tn2 Nt2 Equation 16 Equation 17 When combining these equations, the change of the relative velocity for both vehicles at the impulse point can be calculated from Vt0 Vt c1 T Vn0 Vn c3 N Equation 18 c3 T c2 N Equation 19 with c1 1 1 n2 n2 1 2 m1 m2 I1z I2z Equation 20 c2 1 1 t2 t2 1 2 m1 m2 I1z I2z Equation 21 t1 n1 t2 n2 I1z I2z Equation 22 3 To be able to solve these equations and to calculate the postimpact velocities and rotations two additional assumptions have to be made (see below). The full impact In case of a full impact two additional assumptions are made: 1. No relative movement between both vehicles can be found in the impulse point at the end of the compression phase. Vn c3 Vt c2 Equation 23 Tc 2 c3 c1 c2 Nc Figure 3 Impact configuration. Vn c1 Vt c3 c23 c1 c2 Equation 24 2. The average between compression and restitution momentum is defined by the coefficient of restitution, which is defined according to Equation 6. 20 ACCIDENT INVESTIGATION/Determination of Cause: Reconstruction So the components of the total momentum can be calculated from T Tc 1 " Equation 25 N Nc 1 " Equation 26 These equations are sufficient to calculate all postimpact velocity conditions for both involved vehicles in the case of a full impact. The sliding impact In certain collisions the two vehicles will never reach identical velocities at the impulse point during the impact. In such cases a contact plane has to be defined, along which the two vehicles slide. The impulse point must coincide with this plane. For such a situation the following two assumptions are made: 1. No relative movement between both vehicles can be found at the impulse point at the end of the compression phase in a direction normal to the contact plane. So Nc can be calculated from Equation 24. 2. The direction of the momentum is limited by a friction (m). This value defines the friction between the two impacting vehicles. T N Equation 27 3. The average between compression and restitution momentum is again defined by the coefficient of restitution according to Equation 6, and T and N can again be calculated from Equations 25 and 26. The coefficient of restitution, which can be handled as an input or output parameter, is easy to define. It always lies in the range 0.1±0.3. The higher the deformations of the vehicles, the lower is the coefficient of restitution. Only for very small deformations are values higher than 0.3 possible. Using these equations, the relation between postcrash and precrash velocities can be determined. These equations are used in many different forms to calculate the precrash velocities from the postcrash velocities, mainly for the conventional reconstruction of car accidents, where the reconstruction is started from the rest position. Several simulation models use the same equations to determine the postcrash velocities from the precrash values. Energy equivalent speed As modern cars are mostly designed to absorb energy during a collision, the amount of damage found on the vehicles can also be used to determine the precrash velocity. For most vehicles crash tests are performed and the results published. They show the vehicles' deformation after an impact with a well-defined barrier. Figure 4 shows the deformations of a certain car type in the frontal area when impacting a rigid barrier with speeds of 15 and 48 km h71. Significant differences can be found in the amount of damage sustained by the vehicle. This knowledge can also be used for accident reconstruction. When comparing the deformations found on the vehicle to those of the reference tests, the amount of energy absorbed by the vehicle due to the impact can be estimated. As deformation energies are not very convenient quantities, they are recalculated into velocities and called energy equivalent speed (EES). EES is defined thus: r 2EDef EES Equation 28 m Figure 4 Vehicle damage after frontal impact at (A) 15 km h71, and (B) 48 km h71. ACCIDENT INVESTIGATION/Determination of Cause: Reconstruction Where EDef defines the vehicle's deformation energy and m the vehicle's mass. Thus the conservation of energy can be used in addition: Ekin1 0 Ekin2 0 Ekin1 Ekin2 EDef 1 EDef 2 Equation 29 where Ekini represents the kinetic energy of vehicle i before and Ekini' after the impact. Precrash movement As in many cases the impact speed is not the relevant speed, precrash analyses are also of great importance. They allow determination of the drivers' or other involved persons' reactions. The velocities, relative positions and visibilities at the reaction point can then be investigated and the cause of the accident and the failures of the involved persons or vehicles can be identified. There are several types of failures or combinations of failures, that cause accidents: the vehicle velocity not being adapted to traffic conditions and insufficient driver attention are only just two examples. Whenever accidents are investigated, the situation has to be analyzed from the reaction point. Only thus can real cause be found. The Driver's Reaction The point of reaction can be determined by various methods, depending on the accident situation. In principle, the time from the reaction to the collision position normally consist of three major phases: . reaction time; . lag; . action time. Reaction time The reaction time defines the necessary time to identify the situation, decide the kind of reaction and start the action through activation of certain muscles. It depends on many factors, like age and tiredness, and also on some which are difficult to estimate; for example, an eye blink may increase the reaction time by approximately 0.2 s. One aspect, which is also of great importance, is the visibility of the object. In cases of low contrast or small light differences, reaction time may increase dramatically. This is why so many pedestrian accidents occur at night. In addition, there is a significant difference if the resulting action has to be performed by the arms or by the legs. The greater distance between brain and leg means that an action being performed with the leg will require a significantly longer reaction time. Typical reaction times are between 0.5 and 1.5 s. 21 Racing drivers are known to react during a race within a time of 0.3 s. Lag The lag is defined by the amount of time required by the technical system to act. There is no lag for the steering system but a lag of 0.1±0.3 s for the brake system. This lag is mainly caused by the amount of time necessary to push the brake pedal to such a level that the full brake force is applied to the wheels. One technical solution to reducing this time is the so-called `brake assistant', which automatically applies the full brake force when the brake pedal is pushed very fast. Action time The action time defines the time when the action (mainly braking or steering) is active. Prevention analysis When the point of reaction has been found, so called prevention analysis must be performed. These calculations are used to determine a fictitious scenario where the accident would not have occurred. In this case, parameters like initial velocity, shorter reaction time, better visibility or higher friction on the road are varied. These analyses are used both to determine the influence of the driver's failure and often to change the road design to prevent similar accidents. Sample Case The following sample case demonstrates the analysis of a vehicle±vehicle accident caused mainly by one driver overrunning a `stop' sign. The first step when simulating a new accident is the identification of all involved vehicles. Modern simulation programs to allow access various databases containing all necessary geometric and mass data. In a second step the involved cars can be moved to the `average' collision position. Here their correct overlap must be taken into account. To define the friction conditions and drivers' actions, so-called `sequences' can be given (Fig. 5). They can be defined in a very simple and flexible way. The different steering, brake and acceleration actions can be defined by listing the actions. The values for the individual actions can then be given. The validity of one sequence can be limited by definition of a time interval or a travel distance of the vehicle's center of gravity. The brake or acceleration forces can be given for every wheel independently. This is important to simulate wheels locked during the accident. Changes in the friction due to oil or wet areas can be defined by identifying individual areas. The corresponding friction coefficient must then be specified. 22 ACCIDENT INVESTIGATION/Determination of Cause: Reconstruction Figure 5 Definition of driver actions. After these definitions have been given, the impact can be calculated and the postcrash movement will be simulated automatically (Fig. 6). As a result the movement of the involved vehicles, including their wheel traces, can be seen on the screen and can then be compared to a previously created DXF drawing of the scenario. As an alternative a scanned bitmap can be underlayed. So the preimpact velocities can be varied, as well as all Figure 6 Definition of impact values including results. other impact parameters. PC-CRASH, as one of the major software tools, also provides an optimization tool that allows automatic variation of specific parameters. Through the definition of target functions, the most plausible solution will be found immediately. Figure 7 shows the movement of two vehicles after a 908 impact in steps of 200 ms. A dry asphalt surfaced road was assumed. ACCIDENT INVESTIGATION/Determination of Cause: Reconstruction 23 Figure 7 Vehicle movement after impact: (A) collision, (B) 200 ms, (C) 400 ms, (D) 600 ms, (E) 800 ms, (F) 1000 ms, and (G) 1500 ms after collision, (H) final position. 24 ACCIDENT INVESTIGATION/Driver Versus Passenger in Motor Vehicle Collisions Results The major fault in this case was that the driver of the private car should have stopped before the crossing. From brake traces drawn from the truck before the impact, which had a length of 7 m, the initial speed of the truck was calculated to be 60 km h71. The truck driver reacted 1.7 s before the collision. Driving at a speed of 48 km h71 or less, the accident would have been prevented, as the truck would have stopped before the impact. For these calculations a reaction time of 1 s and a brake lag of 0.2 s was assumed. If the driver of the truck had been driving at a speed of 50 km h71, the truck would have reached the collision position 2.4 s after he had reacted. This means the private car would have continued for 0.7 s and thus have passed an additional distance of approximately 2.3 m, insufficient to prevent the accident. So the accident would have also occurred at an initial speed of 50 km h71 which was the speed limit at the reaction point but the impact speed would have been reduced from 44 km h71 to approximately 15 km h71. See also: Accident Investigation: Motor Vehicle; Determination of Cause: Overview; Tachographs; Driver Versus Passenger in Motor Vehicle Collisions. Pattern Evidence: Vehicle Tire Marks and Tire Track Measurement. Photography and Digital Imaging: Digital Imaging Enhancement. Further Reading Brach RM (1991) Mechanical Impact Dynamics: Rigid Body Collisions. Chichester: Wiley. Day TD and Hargens RL An overview of the way EDCRASH computes Delta-V, SAE 820045. Warrendale, PA: Society of Automotive Engineers. Gnadler R (1971) Das Fahrverhalten von Kraftfahrzeugen bei instationaÈrer Kurvenfahrt mit verschiedener Anordnung der HaupttraÈgheitsachsen und der Rollachse. Thesis, University of Karlsruhe. Kudlich H (1966) Beitrag zur Mechanik des KraftfahreugVerkehrsunfalls. Thesis, University of Vienna. Lugner P, Lorenz R and Schindler E (1984) The connexion of theoretical simulation and experiments in passenger car dynamic. In: Hedrick HJ (ed.) The Dynamics of Vehicles on Roads and on Tracks, Lisse: Swets-Zeitlinger. McHenry RR (1976) Extensions and Refinements of the CRASH Computer Program. Part I: Analytical Reconstruction of Highway Accidents. DOT-HS-5-01124. McHenry RR, Segal DJ and DeLeys NJ (1967) Computer simulation of single vehicle accidents. Stapp Car Crash Conference, Anaheim, California, October 1967. Rill G (1994) Simulation von Kraftfahrzeugen. Vieweg. Slibar A (1966) Die mechanischen GrundsaÈtze des Stoûvorganges freier and gefuÈhrter KoÈrper und ihre Anwendung auf den Stoûvorgang von Fahrzeugen. Archiv fuÈr Unfallforschung 2. Steffan H (1993) PC-CRASH, A Simulation Program for Car Accidents. ISATA; 26th International Symposium on Automotive Technology and Automation, Aachen. Steffan H PC-CRASH 6.0. A Simulation Program for Car Accidents: Users and Technical Manual. Linz: DSD. Steffan H and Moser A The collision and trajectory models of PC-Crash, SAE 960886. Detroit: Society of Automotive Engineers. Steffan H and Moser A The trailer simulation model of PC-Crash, SAE 980372. Detroit: Society of Automotive Engineers. Driver Versus Passenger in Motor Vehicle Collisions W S Smock, University of Louisville, Louisville, KY, USA Copyright # 2000 Academic Press doi:10.1006/rwfs.2000.0749 Introduction The determination of a motor vehicle occupant's role in a vehicular collision is always an important medicolegal question. If the occupants of the vehicle have been ejected or relocated within the vehicle as a result of the vehicular dynamics of the collision, determining the occupants' role at the time of the collision may be difficult. The investigation that coordinates an examination of injury mechanisms, occupant kinematics, vehicle dynamics and the evaluation of trace evidence will facilitate the determination of an occupant's role. Such a determination is critical when criminal charges are considered. It is imperative that, when charging an individual, the investigating agency performs a thorough investigation in order to protect the innocent passenger from being falsely prosecuted as the driver. Variables that Confound Occupant Role Determination `I wasn't the driver' is a statement often made by occupants of an automobile which has been involved in a serious or fatal collision. It is also a statement that may or may not be true. When a surviving occupant presents to an emergency department, it is imperative that care be taken to ensure that any short-lived evidence found on the individual is recognized and ACCIDENT INVESTIGATION/Driver Versus Passenger in Motor Vehicle Collisions collected. It is also imperative that all of a patient's injuries be documented before their appearance is altered in the delivery of patient care. By preserving evidence and painstakingly documenting injuries, the investigating agency insures a high standard of investigation. Statements obtained in the emergency department from the patients should be made part of the permanent record, within quotation marks, by those witnessing their utterances. Allegations of criminal and/or civil liability should be based on the tangible evidence collected from the vehicles, their occupants and the crash scene. Common problems which hinder the investigative process itself often complicate the differentiation of driver from passenger. These impediments may also be used in court as an effective defense against the charges. The following are examples of potential problems: . Occupants are removed from vehicles by wellmeaning bystanders whose statements and observations are not recorded by the investigating agencies. . Physical evidence of occupant movement within the vehicle and trace evidence of occupant and vehicle contact are not recognized, collected and documented. . The surviving occupant's injuries, including pattern injuries, are not photographically documented while the person is in the emergency department. . Evidence standards (clothing, shoes) and biological standards (hair and blood) are not collected from all occupants. . An autopsy is not conducted on the deceased occupant(s). . Substandard analysis of the crash scene prohibits accurate reconstruction of the vehicle dynamics. . Vehicle components found at the crash scene are haphazardly thrown back into the vehicles, resulting in the possibility or supposition of crosscontamination. . Inadequate resources are committed to the evaluation of the incident. . Assumption is made that the owner of vehicle is the driver. . The vehicle is not preserved or is left exposed to the elements, which may lead to destruction or loss of trace evidence. 25 point of impact. This determination is best made by an accident reconstruction expert. Occupant Kinematics In the event of a rapid deceleration of the kind that occurs instantly in crash circumstances, vehicle occupants, restrained or unrestrained, will experience a force which causes them to move initially toward the primary area of impact. This occupant movement or occupant kinematics has been conceptualized as a motion parallel to and opposite from the direction of the force which is developed by the impacting object (Fig. 1). This movement of the occupant, and subsequent contact with the vehicle's components, is dictated by the forces applied to the vehicle through its interaction with the environment. The application of the principles of occupant kinematics will predict in what direction a particular occupant will move, and, therefore, which component within the vehicle they will strike. Occupant kinematics is best determined by a physician/nurse with forensic training in concert with the accident reconstructionist. Injury Mechanisms The correlation and matching of pattern injuries from surfaces and components within a vehicle will reveal an occupant's position during a portion of the vehicle's collision sequence. The most commonly observed pattern injuries are: seat belt contusions (Fig. 2); air bag injuries ± facial abrasions, face and arm lacerations and fractures, and extremity amputations (Figs 3±6); steering wheel contusions; contusions, abrasions and lacerations from impact with window cranks, radio knobs, door latches and dashboard components. Different types of pattern lacerations will also result from contact with the different kinds of automobile glass used in front and side windows (Figs 7±9). Analysis of the occupant's injuries should be undertaken by a physician/nurse trained in forensic medicine. Vehicle Dynamics How the vehicle interacts with the environment will dictate what forces are applied to the vehicle's occupants. The forces applied to the occupants will dictate how the occupants move within the vehicle. When, for example, a vehicle hits a tree head-on, the occupants of the vehicle will move forward, toward the Figure 1 Occupant kinematics is defined as the movement of an occupant within a vehicle. An occupant will experience movement towards the point of impact. This movement is parallel and opposite from the principal direction of force. 26 ACCIDENT INVESTIGATION/Driver Versus Passenger in Motor Vehicle Collisions Figure 2 A seatbelt contusion may provide valuable evidence as to the position of an occupant. This patient's contusion extends from the left lateral neck across the right breast and was the result of contact with the driver's side seatbelt. Figure 5 Contact with the deploying air bag module cover can give rise to pattern fractures of the upper extremities. This open comminuted fracture of the forearm indicates a bending type of fracture from contact with the air bag module cover. Figure 3 (see color plate 2) Contact with deploying air bags will result in injuries to the occupants, including abrasions. This patient sustained superficial abrasions overlying the abdomen, secondary to air bag deployment. Such injuries can be matched to the vehicle's air bag. Figure 6 (see color plate 3) A degloving injury with underlying fracture. This patient sustained an open fracture, with degloving of the forearm, secondary to contact with the deploying air bag. Matching this injury and the blood transferred to the air bag would assist in identifying the role of this patient. Figure 4 A diagrammatic representation of a forearm injury from contact with the deploying air bag module cover. This will give rise to the fracture pattern seen in Fig. 5. Figure 7 Contact with the tempered glass found in side and rear windows will impart a `dicing' laceration to the skin. ACCIDENT INVESTIGATION/Driver Versus Passenger in Motor Vehicle Collisions 27 Figure 8 Sliding contact with tempered glass during occupant ejection will impart a characteristic superficial laceration to the skin. This is characterized by two parallel superficial lacerations 3±8 mm apart. Figure 9 Contact with the laminated glass found in windshields will result in linear lacerations. These lacerations tend to be deeper than the dicing lacerations induced by tempered glass. Trace Evidence cotransference of hair and tissue to the glass and of glass to the tissue (Fig. 14). Collection of this glass from a patient's wound can be matched with a particular window within the vehicle if a glass standard is collected from the vehicle involved. Two types of glass are used in automobiles: laminated, used in windshields; and tempered, used in the side and rear windows. Each of these types of glass will produce a pattern laceration unique to it. The windshield is composed of two layers of glass, laminated together, with a thin layer of clear plastic sandwiched between. This laminated glass will break into shards upon impact; wounds resulting from impact with laminated glass will be linear and incised (Fig. 9). The tempered or `safety glass' is a single layer of glass that breaks into small cubes when fractured. Wounds resulting from impact with tempered glass will appear `diced', punctate and rectangular in configuration (Figs 7 and 8). One of the most critical elements in the determination of the occupants' role in a motor vehicle collision is the collection of trace evidence from the victims and the vehicle. Special efforts must be made to collect clothing and biological standards from all vehicle occupants. The preservation of clothing, shoes and biological standards (including hair and blood) will be invaluable in determining an occupant's role. Examination of the soles of leather shoes may reveal the imprint of the accelerator or brake pedal, or the imprint of the leather floormat (Figs 10 and 11). The preservation of clothing will permit a forensic examiner to compare clothing fibers to those fibers transferred to vehicle components during the collision (Fig. 12). Fabric imprints may also be transferred to components within the vehicle (Fig. 13). Contact with the front windshield will frequently result in the A B Figure 10 (A) Examination of leather-soled shoes may reveal the presence of a pedal imprint. (B) The shoe reflects an imprint from the vehicle's brake pedal and indicates that the wearer of the shoe was, in fact, the driver. 28 ACCIDENT INVESTIGATION/Driver Versus Passenger in Motor Vehicle Collisions A B Figure 11 Examination of the dirt present on the sole of a boot (A) indicated the imprint of the brake pedal (B). The steering wheel may be damaged as the result of driver contact. The steering wheel in Fig. 15A displays rim damage from impact with the driver's mouth (Fig. 15B). Close examination of both driver and passenger air bags will often reveal transference of trace evidence, including hair, tissue, make-up and blood to the bag's surface (Fig. 16). Occupant contact with the deploying air bags will also result in pattern injuries appearing on the patient (Figs 3±6). The air bag module cover ACCIDENT INVESTIGATION/Driver Versus Passenger in Motor Vehicle Collisions 29 Figure 12 Fabric may be transferred from an occupant's clothing to components within the vehicle. Fabric from the passenger was transferred to the tempered glass in this rear window during her ejection. Figure 14 Occupant contact with the front windshield may reveal the transfer of hair, blood and tissue. This evidence can be matched to the standards obtained from the occupants. may also yield valuable forensic evidence. Examination of the module cover may yield transferred tissue or an imprinted fabric pattern. Removal of all air bags from the vehicle should be done routinely in cases where occupant roles are in question, as they will yield a tremendous amount of forensic information. Examination of the seat belt webbing and hardware may reveal the presence of loading marks if the occupant experienced a deceleration of the order of 25 km h71 or greater (Fig. 17). These marks will confirm restraint usage and this evidence can be correlated with seat belt contusions on the occupants. Sample Cases Case 1 Figure 13 Forceful contact of clothing to vehicle components may impart a fabric transfer. A fabric imprint is noted on the steering wheel. Comparison of the weave pattern on the patient's pants to the pattern on the steering wheel confirmed the patient's role as the driver. A 1956 Ford Thunderbird convertible was involved in a collision that resulted in the ejection of both front seat occupants (Fig. 18). One occupant sustained fatal injuries and the other sustained severe, closed head injuries. The surviving occupant had no recollection of the collision and was charged with vehicular homicide as he was the owner of the vehicle. 30 ACCIDENT INVESTIGATION/Driver Versus Passenger in Motor Vehicle Collisions A Figure 16 Examination of the air bag may also reveal the presence of transferred blood tissue, hair and makeup. Collection and preservation of a vehicle's air bag is obligatory if there is a question as to the role of the vehicle's occupants. B Figure 15 The presence of blood on the steering wheel in proximity to a divot of the steering wheel rim (A) from contact with the driver's teeth (B) confirmed the role of the occupant. The investigating agency failed to collect hair or bl