Main Encyclopedia of Forensic Sciences

Encyclopedia of Forensic Sciences

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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.
Categories: Medicine\\Trial
Year: 2000
Edition: 1
Publisher: Academic Press
Language: english
Pages: 1484
ISBN 10: 0122272161
ISBN 13: 9780122272158
ISBN: 012227217X
File: PDF, 40.55 MB
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Overview of a

Edited By
Jay Siegel , Michigan State University, East Lansing, U.S.A.
Geoffrey Knupfer , National Training Center for Scientific Support to
Crime Investigation, Harperley Hall, Crook, UK
Pekka Saukko , University of Turku, Finland
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.
Forensic science laboratories, police departments, academic libraries,
law firms and law school libraries, academic departments teaching
forensics, government agencies, and public libraries.
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) 06/03/2005

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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) 06/03/2005

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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
Price: Order form
EUR 995
GBP 665
USD 995
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999/999 06/03/2005

ACCIDENT INVESTIGATION/Airbag Related Injuries and Deaths



Airbag Related Injuries and Deaths
Determination of Cause: Overview
Determination of Cause: Reconstruction
Driver Versus Passenger in Motor Vehicle Collisions
Motor Vehicle

Airbag Related Injuries and
W S Smock, University of Louisville, Louisville, KY,
Copyright # 2000 Academic Press

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


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
. 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

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.

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



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




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




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



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-


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


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




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


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



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).

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

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

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.


Determination of Cause:
D Rudram, The Forensic Science Service, London,
Copyright # 2000 Academic Press

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
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

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
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
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
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


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
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.

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
. 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
 ˆ v2 =2gs
where g is the acceleration due to gravity and then the
speed of the car leaving the skidmarks is given by:
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


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:
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.

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

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
. 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


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.


. What do they say and are they consistent?
. If, as is normal, they disagree are there any areas of
. 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

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
. 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
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
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.

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

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:
H Steffan, Technical University Graz, Graz, Austria
Copyright # 2000 Academic Press

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.

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


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

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
Equation 1†
 ˆ 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
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 ˆ 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

2 0

1 0

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
Equation 4†
SC ˆ

SR ˆ




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


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


Equation 10†

Vn ˆ V1n


Equation 11†

In addition, the balance of momentum can be formulated for both vehicles

Figure 2 Measured accelerations.


Vt ˆ V1t

Equation 6†

The total exchanged momentum is calculated from
S ˆ SC ‡ SR ˆ 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 ˆ vs1t ‡ !1z n1

Equation 8†

V1n ˆ vs1n ‡ !1z t1

Equation 9†

m1 v0s1t

vs1t † ˆ T

Equation 12†

m1 v0s1n

vs1n † ˆ N

Equation 13†

m2 v0s2t

vs2t † ˆ


Equation 14†

m2 v0s2n

vs2n † ˆ


Equation 15†

The balance of angular momentum can be formulated
I1z !01z
I2z !02z

!1z † ˆ Tn1
!2z † ˆ


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 ˆ Vt ‡ c1 T

ˆ Vn

c3 N

Equation 18†

c3 T ‡ c2 N

Equation 19†

c1 ˆ

n2 n2
‡ 1‡ 2
m1 m2 I1z I2z

Equation 20†

c2 ˆ

‡ 1 ‡ 2
m1 m2 I1z I2z

Equation 21†

t1 n1 t2 n2

Equation 22†



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 ˆ 2
c3 c1 c2
Nc ˆ

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 ˆ Tc 1 ‡ "†

Equation 25†

N ˆ 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 ˆ 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:
Equation 28†

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
Ekin1 0 ‡ Ekin2 0 ˆ 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.


Racing drivers are known to react during a race
within a time of 0.3 s.

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
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


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

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

Driver Versus Passenger in
Motor Vehicle Collisions
W S Smock, University of Louisville, Louisville, KY,
Copyright # 2000 Academic Press

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
. 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
. 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
. The vehicle is not preserved or is left exposed to the
elements, which may lead to destruction or loss of
trace evidence.


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


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

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



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


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


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

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.

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