1. On-Scene Traffic Accident Investigation Level I
Jay Hoekwater

2. Background and Purpose
The success of any traffic accident investigation depends upon the quality and quantity of evidence collected at the scene and during follow-up inquiries. Many training programs in traffic accident investigation emphasize tasks which are totally reliant on proper evidence collection procedures. Often times however, the process of collecting and documenting physical evidence is not addressed in a manner which prepares the officer for that task.

3. On-Scene Traffic Accident Investigation Level I, focuses on the evidence collection process. Special emphasis is placed on evidence recognition and proper evidence collection techniques. Officers successfully completing this course should be able to interpret and collect the evidence at the accident scene and the subsequent follow-up investigation.

4. Definitions
1) An accident is that occurrence in a sequence of events which usually produces unintended injury, death, or property damage.
2) A traffic accident investigation is the thorough examination of all elements contributing to the accident, resulting in a well founded explanation of the series of events which occurred based upon the factual data.

5. Measuring and Diagramming the Accident Scene
Terminal Performance Objective
Given a simulated traffic accident, students will demonstrate the ability to accurately record the accident scene through the use of measurements and diagrams.

6. Enabling Objectives
Identify six results of an accident that should be documented by the use of measurements
Explain two measuring techniques commonly used in traffic accident investigation
Describe the four step measuring process
Demonstrate the ability to measure and diagram traffic accident scenes by applying both measuring techniques

7. Introduction
The biggest complaint of most accident reconstruction specialists is the failure of the On-scene investigator to make satisfactory measurements of the results of the accident. Locating the results of the accident, such as final positions of vehicles is done improperly nine times out of ten. These measurements are crucial to the investigation and provide the foundation needed to establish vehicle to roadway and vehicle to vehicle relationships as well as speed estimates.

8. Walk-Through
Before any measurements can be taken, the accident investigator must make a walk-through of the accident scene. The purpose of this walk-through is to locate, mark, photograph, list and describe all roadway evidence. This is an extremely important step. The investigator should walk-through the entire scene from beginning to end. He should have the following items as he makes his walk-through:

9. Chalk or spray paint, camera, pencil and measurement log sheet (Each piece of evidence must be marked, photographed, listed and described on the measurement log sheet)

10. The following results of the accident should be located:
Everything !

11. Final positions of vehicles, dead and injured persons, and major vehicle parts which have bee detached.
Metal scars
Tire marks
Scars alongside the road
Debris
Damage to fixed objects

12. It is advisable to mark the evidence in a logical progression as it is located, such as a,b,c, As each piece of evidence is located, marked, and photographed it should immediately be listed and described on the measurement log sheet.

13. List and Describe

14. Draw a Field Sketch
The importance of a field sketch must not be overlooked. The field sketch must include all the evidence, view obstructions, traffic control devices, and roadway features. The field sketch should be a representation of the general layout of the roadway and the results of the accident.

15. The investigator should not limit himself to one field sketch
The investigator should not limit himself to one field sketch. He should make as many as necessary to avoid cluttering up the sketch. The evidence should be drawn on the field sketch and it should be marked exactly as it was marked on the roadway and listed on the measurement log sheet. Generally speaking, measurements should not be recorded on a field sketch.

16. The field sketch should also include the direction or north, name of the person making the sketch, date, location, and case number. The field sketch is a permanent part of the case file and should not be discarded when the scale drawing is complete.

17. Establish a Baseline
A baseline is a tape measure stretched and anchored parallel to the accident scene. Any accident scene can be measured from a baseline. The baseline must be straight. It can be lined up on the road edge or fog line providing they are straight. Several hundred feet of road may be involved in some accidents. In those cases, the baseline may have to be moved several times. If the linear measurements are properly recorded, moving the baseline poses no problem.

18. Measure and Record the Measurements
Once the previous steps have been taken, the investigator can begin to measure. Each measurement must be recorded on the measurement log sheet as it is made. Recording measurements should not be a problem if the investigator has listed and described each item to be measured on the measurement log sheet.

19. The number of points to be measured for each item of evidence varies
The number of points to be measured for each item of evidence varies. The following guidelines are suggested.
NOTE: Two measurements are required for each marked point

20. One point: Metal scars and tire marks less than three feet long, small scrapes or dents in fixed objects, liquid debris less than three feet in length, and wheel parts such as detached wheels

21. Two points: Human body (head and foot), vehicle final rest positions (at least two wheels), straight skid marks (beginning and end), straight metal scars more than three feet (beginning and end), long stretches of damage to a guardrail (beginning and end), liquid debris dribble paths

22. Three points or more: Curved tire marks, straight skids with angles (offsets), large fields of debris

23. Measure and Record Measurements
The coordinate measuring technique and the triangulation measuring technique are the two accepted measuring methods used by traffic accident investigators.
You’re not paying attention son!

24. Coordinate measuring is measuring from the baseline at right angles to the point. The first measurement is the distance from zero to a point perpendicular to the object to be measured. The second measurement is the distance from the baseline to the point.

25. Coordinate measuring has some disadvantages
Coordinate measuring has some disadvantages. It is time consuming, it requires two people, and as the distance from the baseline increases, the accuracy tends to decrease.

26. Method for recording coordinate measurements: five feet three inches from 0, and four feet six inches from the baseline

27. Triangulation measuring involves measuring to the point from two points on the baseline, two fixed objects, or two points already measured.

28. The distance between the two points on the baseline forms the base of the triangle and the distance from each point forms the other two sides.

29. Triangulation measurements do not have to be made from two fixed objects. Triangulation is not more difficult than coordinate measuring and it is more accurate, faster, and can be done by one person providing he has a hammer and cement nails.

30. Permanently Locating the Baseline
Once all the measurements have been taken and recorded, the investigator may want to mark the beginning and end of the baseline or use measurements to establish its position relative to a fixed object(s). This is done so the baseline can be placed in its exact location if the investigator should have to return to the scene to get additional measurements.

31. Safety
When measuring, never assume that motorists will see you or try to avoid you if they do see you. Do not turn your back on traffic. Always wear a safety vest and plan measuring with safety in mind. Your safety is your responsibility.

32. Diagramming
Most scale diagrams of an accident scene can be drawn with nothing more than a pencil, template, and bow compass. However, other equipment is available which will make the job easier and also enhance the appearance of the drawing.

33. Diagramming Equipment
The following is a list of additional drawing equipment useful in making accident scene drawings:
Engineers’ triangle
Flex curve
T square
Engineers’ scale
Drawing table
Lettering guide
Computer with CAD Program

34. Traffic Template
Scale 1/10 or 1/120 and 1/20 or 1/240

35. Bow Compass Methods for drawing parallel lines
Methods for bisecting lines
Triangulation

37. Conclusion
Measuring and diagramming the accident scene are key elements in documenting the results of the accident found at the scene. The key to successful measuring is to have a methodical approach and practice that approach on every accident. Remember, law enforcement is charged with the responsibility of investigating traffic accidents. Documenting the accident scene is a critical element of a thorough investigation.

38. Planning for Traffic Accident Investigation
Terminal Performance Objective
Given a simulated traffic accident, students will exhibit the ability to correctly plan and initiate an effective traffic accident investigation.

39. Planning for Traffic Accident Investigation
Enabling Objectives
Identify six traits common to competent traffic accident investigators who plan and initiate effective investigations.
Identify the five stages of planning and initiating traffic accident investigations.

40. Introduction
Officers who conduct thorough and effective traffic accident investigations are successful because of the planning they have put into their task. Any officer who hopes to succeed in an activity as complex as traffic accident investigation must expect to put maximum effort into planning his investigation.

41. This instructional unit is designed to help officers understand the desired traits for accident investigators, training needs, equipment needed to conduct accident investigations, and the need for an investigative plan.

42. Investigator Traits
Successful accident investigators generally have several traits which insures their success The following is a list of some of those traits:
They have a particular aptitude for accident investigation.
They have a good basic understanding of accident causes and investigative techniques as well as a general knowledge of accident reconstruction principles

43. They are methodical and thorough
They do not mind working
They are willing to improve their expertise through advanced training and self study
They consider the factual data only and do not make ill-advised predeterminations

44. Training
An accident investigator’s effectiveness will depend upon his training and experience. Some aspects of an investigation can be learned with practice. Other activities such as describing marks left on the road by an accident and measuring to locate the results of an accident, require specialized training.

45. This need is demonstrated by the fact that officers who have attended several serious accidents continually make measurements that are unusable. Training becomes especially important when information collection can not be reduced to filling in the blanks of a motor vehicle accident report form.

46. Equipment
The tools needed for information gathering depends on the extent the accident is to be investigated. No special equipment is necessary to fill out the motor vehicle accident report form. The most obvious results of an accident are in the form of damage. It seems reasonable therefore, that all damage should be documented through notes, photographs, and measurements. Roadway dimensions and the location of traffic control devices must also be documented.

47. The following equipment is useful in the
investigative process:
Forms (an excellent guide to routine data
collection)
Clipboard
Pens, pencils
Note pads and graph paper
35mm Camera, flash, color film

48. Planning the On-Scene Investigation
Many times accident investigators wish that they could go back and investigate the accident all over again. Evidence may have been overlooked, or a vital activity forgotten. Quite often these kinds of mistakes are the result of a lack of planning on the part of the investigator. There are five times during the investigation when the situation can be evaluated well enough to plan what to do next. The five planning stages are:

49. On Learning of the Accident

50. On Arrival at the Scene

51. When the Emergency is Under Control

52. When Urgent Data Collection is Complete

53. When Work at the Scene is Finished

54. Learning about the Accident
Ask when and where the accident happened and severity
Decide urgency of response and best route to the scene
Find out if traffic is blocked and if other emergency vehicles are on the way
Arrange for additional help
Start for the scene

55. Be alert for vehicles leaving the scene as they might be carrying injured parties or they might be hit-and-run vehicles
Look for conditions confronting a driver approaching the scene such as low visibility, view obstructions, and traffic control devices

56. Arrival at the Scene
Select a safe parking area which will not block traffic

57. Look at bystanders and others in an attempt to locate drivers, witnesses, and volunteer helpers

58. Watch for fire and electrical hazards and get them under control

59. Look for traffic hazards, put out warning devices and get help with traffic control

60. Look for physical evidence and have it guarded until it can be examined, collected, or located by measurements

61. Care for the injured and ask for emergency assistance if necessary

62. Locate drivers and give out hit-and-run descriptions if necessary

63. Arrange to have the roadway cleared, delay removal of vehicles, except to aid injured, until final positions are marked

64. When the Emergency is under Control
Ask preliminary questions of drivers and be alert for signs of intoxication, confusion, or nervousness
Gather clues for hit-and-run investigations
Question other witnesses especially those who are anxious to leave
Examine driver condition, look for signs of alcohol or drug use (see OCGA for further clarification)

65. Question drivers more carefully, collect all data and ask questions regarding what they saw and did
Observe vehicle condition, note lights, light switches, gear position, and tires

66. Photograph all damage to roadway property, vehicles, and final positions

67. Measure to locate marks on the road and final positions, record the place to which injured persons and damage vehicles are to be taken

68. Have road cleared if traffic is obstructed

69. When Urgent Data is Complete
Make arrests or issue citations as necessary
Have involved parties exchange names and insurance data
Complete on-scene examination of vehicles
Make additional photographs of view obstructions, traffic control devices, and any other information

70. Make additional measurements if possible, revisit the scene later if the location will be difficult to measure
Have location cleaned up

71. When On-Scene Work is Finished
Notify relatives of dead and injured and owner of the vehicle
Inform other agencies of conditions needing attention
Organize notes
Complete factual data on report
Complete investigation and report

72. Conclusion
Remember your investigation will only be as good as the planning and preparation you put into it. What you do is important. Develop a good plan and practice it.

73. The Human Element in Traffic Accident Investigation
Terminal Performance Objective
Given a simulated traffic accident, students will demonstrate the ability to accurately gather information and evidence available through principals and witnesses.

74. Enabling Objectives
List three elements present in every traffic accident
List four kinds of information that must be obtained from each one of the three elements in a traffic accident
Identify three statement taking guidelines
Identify three pre-accident conditions associated with drivers and pedestrians

75. Introduction
Obviously the human element is of major importance in any traffic accident investigation. The major contributing factor in automobile crashes is human error. Accident investigators must realize the importance of collecting all the information about the accident from those involved. This is no small task and quite often it is as difficult as collecting other information about the accident.

76. Traffic Accident Elements
Three elements are involved in every traffic accident:

77. Roads
Vehicles
People

78. For each one of the three elements accident investigators must obtain four kinds of information:
Identification
Description
Condition prior to the accident
Results of the accident on the element

79. Locating Persons Having Information
Before information can be gathered regarding the identification of persons involved in an accident, those persons must be located.

80. Drivers
Finding drivers is the first thing to be done after the emergency at the scene is under control. Often, the driver will be the center of attention or the one doing something. The following hints are useful in locating drivers:

81. Two people standing by a vehicle engaged in a discussion
A person writing something on a piece of paper
A person inspecting vehicle damage, lifting the hood, or picking things up around the vehicle

82. The following three situations make finding
drivers difficult:
Occupants are dead or too seriously injured to question
The survivor says the dead occupant was driving
Occupants fail to reveal or make false claims about who was driving

83. Always be prepared to prove who was driving the vehicle.

84. The natural assumption is that the owner of the vehicle was driving
The natural assumption is that the owner of the vehicle was driving. This assumption will bring acceptable results in some cases. However, do not always accept such an assumption as fact. Seek additional information from witnesses and physical evidence in making driver determinations.

85. Witnesses and Passengers
As soon as possible the accident investigator should look for witnesses and passengers. Ask people at the scene if they saw the accident. Often witnesses will be speaking to a driver, talking among themselves, or examining damage. People who did not witness the accident but arrived on the scene prior to the officers arrival may also be useful witnesses.

86. Identification
Recording identification information from people involved in an accident is a simple process. Usually the motor vehicle accident report form provides the information necessary.

87. Others at the scene of serious accidents who
need to be identified are:
Pedestrians involved
Passengers
Ambulance drivers
Tow truck operators

88. Other police officers
Witnesses
First on the scene
Anyone else having important information

89. Levels of Inquiry
Often, accident investigators depend entirely on information provided by those involved in the accident. This information can be unreliable in some cases. Physical evidence should be used more extensively than witness statements. Yet witness statements can be useful for interpreting the results of the accident. Proper use of physical evidence for determining what took place should not lessen the importance of finding out what people know about the accident.

90. There are two levels of inquiry regarding the gathering of information from the people involved.

91. On-Scene Inquiry
In theory all information about the accident should be gathered at the scene. In practice this is impossible for a number of reasons.

92. The on-scene inquiry should focus on the
following information:
Routine identification of drivers, passengers, and witnesses
Inquiries about general vehicle condition (blowout, brake failure, general vehicle condition)

93. Questions about events (speed, maneuvers, final positions)
Questions about tire marks (panic braking, etc)

94. Follow-up inquiry
The follow-up inquiry usually takes the form of written statements. It is important to have a record of what a person says about an accident.

95. When taking a statement try to accomplish
three things:
Find out what the person will or will not say about the accident
Reduce the statement to writing
Attempt to get the person to agree to what has been written

96. The following statement taking guideline
may be helpful:
When
Try to arrange the statement interview at a
time convenient for the informant.

97. Where
Arrange for the statement to be taken at a place which is comfortable and convenient for the informant.

98. How
Be objective, ask positive questions (please tell me what you saw), ask specific questions that are easy to understand, do not argue, do not suggest answers, be diplomatic, courteous and understanding.

99. Questions to be Considered
General questions at the scene will yield the most significant information about those involved. For minor accidents, no other information may be needed However, for more serious accidents additional follow-up questions are usually needed.
Questions about the trip (24 hour background check)

100. Questions about the results of the accident
Miscellaneous questions about tire marks, vehicle condition, driver condition, and other vehicle occupants

101. Driver/Pedestrian Pre-Accident Condition
Since driver behavior is a factor in nearly every traffic accident, the investigator must attempt to determine driver condition just prior to the accident. The investigator should be alert for and consider the possibility of the following clues regarding driver condition:

102. Obvious physical handicaps
Temporary disabilities such as pre-accident injuries, fatigue, and alcohol or drug impairment
Indications the driver was pre-occupied or distracted
Contents of vehicles which suggest driver condition
Nature of the trip (may suggest fatigue or intoxication)

103. Documenting Injuries
Documenting injuries to those involved in traffic accidents involves more than just recording those injuries to fulfill reporting requirements. Injuries are just another form of damage which has to be considered and documented. If done properly injury patterns can assist the accident investigator in concluding how the accident occurred.

104. Procedures for Injury Documentation
Make photographs of injury patterns of persons killed in the accident. This can be done at the hospital or morgue Try to include a measuring device in each photograph
Obtain a copy of all reports regarding injuries (from ambulance and hospital personnel if possible)
Request autopsies (prosecutable, suspicious, etc.)

105. Conclusion
The human element is an important piece of the investigation. The approach to obtaining the information should be as methodical and thorough as any other aspect of the investigation.

106. The Roadway Element in Traffic Accident Investigation
Terminal Performance Objective
Given a simulated traffic accident , students will demonstrate the ability to accurately identify and interpret roadway evidence.

107. The Roadway Element in Traffic Accident Investigation
Enabling Objectives
Recognize and analyze tire mark evidence
Recognize and analyze metal scar evidence
Recognize and analyze debris
Recognize and analyze final positions of vehicles and bodies
Recognize and analyze signs a vehicle left the ground

108. Introduction
In some fatal accidents there may be no witnesses to explain how the accident occurred. In other cases, drivers or pedestrians may not know what took place or may imagine events which did not take place. Many accident investigators are at a loss if someone is not on the scene to tell them what happened. If they rely on someone telling them how the accident occurred they may ignore the physical evidence.

109. This instructional unit focuses on the identification and interpretation of roadway evidence. Once collected and interpreted, roadway evidence allows the investigator to establish vehicle to roadway relationships that are so critical to the investigation.

110. The best time to examine the accident scene is as soon after the accident as possible. Almost every traffic accident leaves some physical sign of what happened. Properly interpreted, roadway evidence can not be disputed It may not explain all that took place, but it can supplement statements by witnesses, prove or disprove theories of what happened, and guide the direction of the follow-up investigation.

111. Record the Information
Information about the road after a traffic accident must be recorded under the same four general headings that are also used for data about people and vehicles.
Identification of the accident location
Description of the road
Condition of the road at the time of the accident
Results of the accident on the road

112. Skid Marks General information
A skid mark is a friction mark caused by a tire that is locked and not free to rotate. The tire can be locked from braking or collision damage Most skid marks on the highway represent successful evasive tactics; the vehicle is braked to a stop before collision. They are often thought of as burned rubber.

113. The black mark left on a bituminous pavement, by a sliding tire, is actually the tar or asphalt softened by heat generated from friction and smeared on the surface as the tire slides across it. On Portland cement concrete surfaces bitumen is not an ingredient in the road. The friction marks on cement are usually caused by the tire rubber being abraded off by the roadway surface. Burning or severe softening rarely occurs with ordinary tires.

114. Spackling

115. Abraded Tire Grindings

116. Asphalt: A heavy black smear showing some rib markings (striations)
Portland Cement: A nearly invisible whitish track ( a black mark may be noticeable in some instances for a short period of time)

117. Soft Material: The sliding tire pushes material ahead and to the side causing a furrow
Abrasive Material: Surface scratches
Pavement Cleaning: Erasing caused by the sliding tire removing dirt or water from the surface

118. Skid Mark Life Kind of mark Weather Amount of traffic
Road repairs or construction
Surface
Type of tire

119. Skid Mark Characteristics
Now pay attention son!

120. Skid marks are relatively straight but they may swerve to the lower edge of the highway
Skid marks are usually less than 300 feet in length

121. Usually there are four marks present from a four wheel vehicle but there may be two, three, or one in that order of frequency
Marks made by left and right tires are generally equally dark and equally wide

122. Front tire skid marks are usually more prominent than rear tire skid marks
Where a skid mark begins it is the width of the tire tread, sometimes it may be a little wider, but almost never narrower

123. The point at which a skid mark begins can usually be located within a few feet
A skid mark nearly always ends abruptly either where the vehicle stops or where the collision begins
Skid marks often show striations quite clearly and they are always parallel to the mark

124. The outer edges of skid marks are sometimes more prominent than the middle, but usually both edges are equally distinct

125. Front and Rear Skid Mark Differences

126. 1) Length – Vehicles are designed so the weight distribution is nearly equal for each tire. During braking the road applies a retarding force at the tire road interface. The force of inertia tends to keep the vehicle moving forward. These forces cause the vehicle to pitch forward. The weight is shifted from the rear to the front tires.

127. If the brakes are equally strong, front to rear, the unloaded rear wheels would slid first, causing an unstable situation and reduces possible brake effectiveness. The development of a braking system having stronger brakes in the front than in the rear, was designed to correct the problem. The improved system causes front wheels to lock first and slide first in most cases. This causes different lengths between front and rear wheel skid marks.

128. 2) Tire over-deflection – The weight shift caused by a braking vehicle overloads the front tires with respect to the air pressure in them. Consequently, the front tires over-deflect or “cup”. When over-deflected, the edges of the tread carry more weight than the middle and also develop more friction and heat. The result is that the edges of the tire leave darker marks than the middle, making the typical front wheel skid marks.

129. The prominent edge marks are a useful means of deciding whether the mark is from a front or rear tire. Occasionally rear tires make over deflected skid marks. This can occur when rear tires are considerably overloaded, for example when a pickup truck is carrying to much cargo.

130. Skid Mark Irregularities

131. Gaps in skid marks occur when a vehicle makes more than one set of skid marks, one after another. The gap is usually 10 feet or more in length. Gap skid marks are more likely to be found in pedestrian accidents.

132. Skip or bounce skid marks are caused when the tire is repeatedly interrupted or narrowed

133. The following three circumstances cause skip or bounce skid marks.
Bouncing during braking
Road bumps or holes
Collisions
The distance between the interruptions is usually three feet or less.

134. Collision scrub marks are caused when damage rather than braking causes a wheel to slide. They are usually ten feet or less in length.

135. During a collision the force on the tire may be very great for an instant. Therefore, these marks may be very conspicuous in some instances. Other times, they may be inconspicuous if the pavement does not easily show skid marks.

136. Once the additional downward force caused by impact releases, the mark changes in appearance. After impact the mark may stop or change to a scuff mark if the wheel is free to rotate. If not it may continue to slide but it will leave a lighter mark.

137. Broadside skid marks are not caused from braking, yet they are skid marks since the wheels are not turning. Such a circumstance occurs momentarily during a yaw, if the yaw has continued far enough so that the vehicle is sliding sideways.

138. Offset skids are like collision scrubs because they mark the position of a tire at the onset of the collision. They are good indicators of the area of impact. They are often the end of the pre-collision skid and the start of the post collision skid.

139. A swerve is a slight deviation from a straight ahead path
A swerve is a slight deviation from a straight ahead path. Skid marks often show deviations from straight paths for reasons other than collisions. A skidding vehicle is susceptible to sideways movement due to the fact that it has exceeded its friction resistance to further motion in any direction. When this happens side forces, which would have no effect on a rolling vehicle which is being steered, can produce swerve in a skidding vehicle.

140. The following can cause a swerve to occur:
Cross slope of the road (super-elevation)
Unequal road surfaces (different coefficient of friction)
Unequal brake

141. Post Collision Skid Marks
Collisions usually cause skid mark irregularities in the form of an offset, a skid, swerve, or abrupt termination. A tire which was not skidding before collision may be on a wheel locked by collision damage. A tire that was skidding before impact may leave no skid mark after impact. This could be caused if the driver no longer applied the brakes or if damage reduced or discontinued contact between the tire and the road.

142. After collision skid marks reveal a great deal about how and exactly where a collision occurred. They may also be important in estimating after impact and pre-collision speeds. All skid marks should be photographed and measured regardless of whether they occur before or after collision.

143. Impending Skids (Skid Mark Shadow)

144. Recording Skid Mark Observations
Once skid marks have been located at the accident site the job of recording these marks begins The following should be recorded:
Location of the beginning and end of each mark
Description of each mark (if you are sure it is a skid mark, be prepared to explain the characteristics that make it such; if you are unsure simply call it a friction mark or tire mark)

145. Direction of the skid (skid marks normally have a faint beginning and an abrupt end)
Measurements of skid marks (for placement not length)
Photograph all marks
Measure track width of marks and vehicle from center of the tread on one side to the center of the tread on the other

146. Accident Significance
Skid marks are the most common type of road evidence and the most easily recognized When evaluated properly skid marks may disclose the following:
Vehicle to roadway relationships when the mark was made
Direction of travel prior to and after the collision

147. Area of impact
Mechanical or tire failure
Speed before and after impact
Identification of the vehicle (hit and run)

148. Yaw Marks General information
There are other kinds of tire friction marks besides skid marks. Yaw marks are scuff marks and they are made by a tire which is rotating and sliding on a pavement or other surface.

149. A yaw mark is a scuff mark made on a surface by a rotating tire which is slipping more or less parallel to its axis. The term yaw means that the vehicle is rotating about its vertical axis as it moves along its path.

150. Yaw Mark Varieties
Like skid marks, yaw marks appear differently depending on the road surface Usually yaw marks are lighter than skid marks.

151. Yaw Mark Life
Yaw marks do not last nearly as long as skid marks.

152. Yaw Marks
Characteristics- Yaw marks are always curved because they result from steering. Striations will also be present and they appear as oblique marks nearly crosswise of the mark

153. Recording Yaw Mark Observations
Measurements of the path of curvature including any crossover marks
Photograph marks so striations can be seen

154. Accident Significance
Yaw marks may be used in some cases to determine a vehicle’s speed. They can also be used to show the vehicle roadway relationships.

155. An acceleration scuff is a scuff mark made when sufficient power is supplied to the driving wheels to make at least one of them spin on the road surface. On pavement the marks look similar to a braking skid mark. On soft or loose material the spinning wheel kicks loose material backwards out of the furrow.

156. Acceleration Scuffs Accident significance
Acceleration scuff mark evidence is not common in traffic accidents. However, accelerating a vehicle in this manner could cause a loss of control which could result in an accident. Acceleration scuff marks may indicate reckless driving.

157. Flat Tire Scuff Marks (Flop Marks)
General information
Flat tire scuff marks are made by an over deflected tire. Remember, over deflected means seriously under inflated or overloaded.

158. Flat Tire Scuff Characteristics
Flat tire marks may extend for many miles along the road. Finding their beginning may be difficult since it is so faint. The mark will usually end where the vehicle was driven off the road to change the tire.

159. Accident Significance
If a flat tire mark does lead up to the area of impact and the vehicle that it came from does have a flat tire, you may have an indication the tire failure contributed to the accident. Quite often drivers may claim a tire failure caused the accident.

160. This is often true in head-on accidents
This is often true in head-on accidents. In many of these cases the tire was disabled during impact and not prior to impact. Therefore, it is important to examine the tires and the road after an accident to determine when the tire failure occurred.

162. A tire imprint is a mark on the road or other surface made by a rolling tire. Imprints will usually show the pattern of the tire tread that made it.

163. Tire Imprints Imprint characteristics
Imprints are made by a tire that is rolling and not slipping. The imprint is usually equally clear for all tires and is the same width as the tire making the imprint. They always start strong and usually end gradually. If striations are present they will be parallel to the mark and the tread design may show.

164. Accident Significance
Imprints are not normally as significant at the accident scene as other tire mark evidence. Sometimes they are confused with skid marks. They can be significant in showing where a vehicle ran off the pavement and came back on again as sometimes occurs prior to a head-on collision.

165. Road scars are marks made on the road or roadside usually by some metal part of an accident vehicle

166. Scratches and scrapes are made with little pressure by metal body parts dragged across the surface. If they are narrow they are scratches and if they are broad they are scrapes. Scratches are useful in determining where a vehicle overturned. Scrapes can be useful in locating the point of maximum engagement.

167. Be alert for marks left by a vehicle being towed through the accident scene.

168. Gouges are places where the pavement has been dug out by strong metal parts which have been forced down on the road.

169. Chips are small deep gouges where chunks of paving have been dug out as might be done with a pick axe. Usually a chip is made when the metal object strikes the road with a force greater than the vehicle’s own weight, a force which can only be produced by collision. This makes chips a good indicator of are of impact.

170. Chops are broad, shallow gouges such as could be made by an axe chopped at an angle into the pavement. Vehicle frames and rims are some vehicle parts which commonly make chops. Chops are likely to occur at maximum engagement and may indicate direction.

171. Grooves are long narrow gouges
Grooves are long narrow gouges. They are made by projecting metal parts and wheels and may continue for some distance beyond maximum engagement.

172. Scars on fixed objects may be found on the road or adjacent to it
Scars on fixed objects may be found on the road or adjacent to it. They may be dented guardrails, damaged traffic signs, or damage to utility poles or trees. They can be useful in determining the path of a vehicle and its final rest position.

173. Road scars can help to locate vehicle to roadway relationships throughout the collision sequence. In order to show vehicle to roadway relationships the marks will have to be matched to the vehicle which made the marks. Occasionally, these marks can be helpful in speed determinations.

174. Debris is loose material scattered at the scene as a result of a traffic accident.

175. Kinds of debris – Underbody debris sticks to the underside of a vehicle and is dislodged during collision.
Vehicle liquids may escape from their containers during the collision. Their pattern on the road is often overlooked but it can be significant.

176. Vehicle parts are usually present at an accident scene
Vehicle parts are usually present at an accident scene. In many cases vehicle parts are not as significant as some other forms of debris. They can be important in some circumstances such as a hit and run accident.

177. Solid cargo can be used in some instances to establish direction of travel.

178. Debris Accident significance
When debris is dislodged during the collision sequence it continues to move in the direction the vehicle was moving and at approximately the same speed until it strikes something. It is usually not a good indicator of area of impact because of the way it scatters. Debris can be useful in determining the flow of the accident, speed in some cases, and final positions.

179. In some accidents a vehicle may leave the ground for a short distance
In some accidents a vehicle may leave the ground for a short distance. This may happen due to a flip or a fall.

180. Signs a vehicle left the ground can be significant in showing speed in some cases and the vehicle’s path of travel.

181. Final positions – The final position is the exact location where a vehicle or body comes to rest after a traffic accident.

182. Uncontrolled final positions are reached by vehicles or bodies unintentionally after collisions. Locate the position of the vehicle by measurements whether it is on or off the road

183. Locate the body by measurements if it is outside the vehicle.

184. Final positions must be established even if the vehicles or bodies have been moved before the officer arrives.

185. This is done by witnesses and observing tire marks and some kinds of debris.

186. Controlled final positions are those to which vehicles or bodies are moved to on purpose after the collision. These need to be noted but are less significant than uncontrolled final positions.

187. Conclusion
The importance of recognizing, interpreting and recording road evidence can not be over emphasized. As with any other evidence it must be photographed and measured properly. The biggest shortcoming in police accident investigations is the failure to properly interpret and collect road evidence.

188. The Vehicle Element in Traffic Accident Investigation
Terminal Performance Objective:
Given a simulated traffic accident, students will demonstrate the ability to accurately identify and examine evidence from vehicles.

189. The Vehicle Element in Traffic Accident Investigation
Enabling Objectives:
Recognize and analyze six types of vehicle information that must be collected at the scene
Identify two means for documenting vehicle damage at the accident scene
Recognize two types of vehicle damage

190. Introduction
The complete evaluation of accident vehicles is just as important as the complete evaluation of the drivers and roadway evidence. Traditionally, vehicle evaluations have been overlooked by those responsible for investigating accidents.

191. Proper vehicle examinations can assist in the determination of vehicle to vehicle relationships, occupant information and movement, vehicle to roadway relationships, mechanical defects, and speed in some cases. This information is essential in the formation of a fact based opinion of how the accident occurred.

192. The Vehicle Element
Some aspects of the vehicle inspection can take place at the scene while other vehicle information may have to be collected later. The accident investigator must recognize that accident vehicles are evidence which has to be protected and evaluated. Valuable information from the vehicles is sometimes lost or tampered with because the accident investigator did not have the vehicles impounded in a secure location.

193. Information
Remember vehicles show the obvious results of the accident in the form of damage. They may also reveal other information about the trip, occupants, and pre-accident condition. All of this information is extremely important to the investigation.

194. Be sure it is properly recorded in the form of measurement, photographs, and notes.

195. Record the Information
Information about the vehicles involved in a traffic accident must be recorded under the same four general headings used for the human and roadway elements.
Identification of the vehicle
Owner’s name and address
Vehicle identification number
License number

196. Description of the vehicle
Size and general structure (motorcycle, sub-
compact, full size)
Body style and appearance (2 dr sedan, 4 dr
hard top, wagon, bus, etc)
User or service (private, rental, government)

197. Condition of the vehicle at the time of the accident
Results of the accident on the vehicle

198. On-Scene Data Collection
Officers investigating accidents must be able to establish priorities in on-scene data collection. The following order may serve as a guide for data collection regarding vehicles:

200. Identification Information
Identification information is the next most important vehicle information which has to be collected at the scene. This enables anyone conducting a follow-up examination the assurance of examining the right vehicle.

201. Vehicle Damage
A general survey at the scene is usually sufficient since the vehicle can be more thoroughly examined at a later time. One main reason for this examination is so the investigator can determine if additional damage was done when the vehicle was removed from the scene. This is extremely important and is done in two ways:

202. Photograph accident vehicles from the front
rear and sides. Take good notes.
Make notes on the condition of lamps, major
detached parts and tires.
Vehicle contents should be noted at the scene
if possible. This information may not be
available later on.

203. Match damage – Generally the best time and place to match contact damage on the vehicles to the marks on the road is at the scene. Gouges or scrapes on the road will nearly always correspond to abrasion or breakage of vehicle parts.

204. Match Damage
Some damage to the body of the vehicle may not be obvious but will be equally important. Damage to the underside of a vehicle can be observed while the vehicle is being lifted for towing.

205. Locked Wheels
Knowing which wheels were locked after the accident is often important. Sometimes simple observations of damage will determine whether a wheel could have rotated freely. In some cases the best time to determine this is when the vehicle has been lifted for towing.

206. When the car is towed across the ground watch the wheels to see which ones turn. If they do turn, note if the drive shaft has been disconnected to allow them to turn. Take good notes.

207. Follow-up Data Collection
At the scene the vehicle is given a general inspection for noting conditions and results of the accident. Serious accidents almost always require a more thorough follow-up vehicle inspection Sometimes these inspections focus on specific problems the investigator is considering. In addition to specific problems, the accident investigator should consider the following suggestions for a follow-up vehicle inspection:

208. Officers should check for manufacturer recalls on all of the vehicles involved in the collision.

209. Types of Damage
Contact damage is damage to any part of a motor vehicle by direct contact with some object which is not part of the vehicle. There are four things which can cause contact damage.

210. People
Ground Contact
Other Vehicles
Fixed Objects

211. Contact Damage can be either internal or external
Contact Damage can be either internal or external. It is usually indicated by closely compacted, crumpled body parts with fine hard scratches in the surface of the metal; smearing of the paint; ragged tears and punctures in sheet metal.

212. Induced damage is damage to any part of a motor vehicle caused by some other part of the same vehicle or by the shock of the collision. Induced damage is usually indicated by folds, bends, creases, and wrinkles.

213. Signs of ground contact – Sometimes a more detailed examination of the vehicle is required to determine which parts of the vehicle contacted the ground. When the vehicle part that made the mark on the ground is identified, it should be photographed and measured. Remember to match the damage.

214. Signs of ground contact – Road surface material or chunks of grass and dirt may also help the officer make determinations about which part of the vehicle made the marks on the road or adjacent to the road. Grass pinched between the tire and the rim can be significant also.

215. Tires and Lamps
Follow-up tire examination should focus on a damage description of the tires and wheels as well as tread depth, air-pressure, and description of each tire. It may also be necessary to match the tire with the marks in the road. Remember, make good notes, photographs, and measurements as needed.

216. Follow-up lamp examination should focus on a damage description of each lamp, and switch position. If lighting is in question the lamps should be removed carefully, identified completely, and stored securely. Special care should be taken with filaments as they are very fragile and essential to any lamp examination. Light switches should not be turned on for the purpose of examining lamps.

217. Collect lamps anytime lighting is in question.

218. Sources of injury to passengers – The damage to the interior of a vehicle should be matched to the injuries sustained by the occupants.

219. In some cases this may not be possible but the damage should be documented with photographs and notes. Remember, all the damage has to be documented and matched to the object causing that damage whenever possible.

220. Measuring Vehicle Damage
In some cases photographs alone are not a sufficient record of vehicle damage. If damage is going to be the basis for speed estimates, detailed vehicle measurements will be needed. Damage measurements are also helpful in determining direction of thrust (principal force).

221. Conclusion
The importance of properly interpreting and collecting vehicle evidence can not be over emphasized. As with other types of evidence make good photographs, measurements, and notes.

222. Traffic Accident Photography
Terminal Performance Objective
Given a simulated traffic accident, students will demonstrate the ability to recognize and coordinate the collection of photographic evidence.

223. Traffic Accident Photography
Enabling Objectives:
List three reasons photographs are used in traffic accident investigation
Identify six things that should be photographed at the accident scene

224. Introduction
Photography is an important part of any investigation whether it be an accident or criminal investigation. Photographs are just one means by which information can be recorded. Photography is an indispensable means of recording certain kinds of accident information and a useful supplement in recording many other kinds.

225. Why Use Photographs Reminder
Photographs are useful to refresh an investigator’s memory about something seen in the past. They are also useful for briefing new investigators to the case.

226. Use of Photographs Credibility
Photographs are generally regarded as being free from the bias that may prejudice verbal statements or written reports. They are an effective way of verifying an officer’s reports and observations.
Recording Evidence

227. The Process
Who makes the photographs

228. Police accident investigators arrange for
photographs to be made at the scene in one of three
ways:
The investigating officer makes the photographs
An ID technician is called to make the photographs
A professional photographer makes the photographs

229. When Should Photos be Made
This may vary from one accident to the next In most serious accidents photographs will have to be made at the scene as soon as possible. Photograph things that will change first. Final positions of vehicles should be photographed as soon as possible so they can be removed and traffic flow restored.

230. What Should be Photographed
On-scene photographs should show how the situation appeared when the vehicles came to rest, how objects were arranged and how things were related to each other. The following things should be photographed:

231. Final positions of vehicles and people
Road Evidence
Marks off the road and damage to fixed objects
Recognizable land marks and approach view of the drivers from their eye level
All four sides of the vehicle involved

232. Photographing Road Evidence
Photographs of road evidence must show clear detail so tire marks and other road evidence can be seen. Close-up photographs are sometimes required. Photograph all relevant marks. When in doubt take a picture. It is a good idea to include a measuring device in the photographs of road evidence.

233. Photographing Vehicle Damage
Photographs of vehicle damage should be taken at the scene whenever possible. This is done so subsequent damage caused by towing will be noted. More detailed photographs of vehicle damage can be taken later. Damage photographs should include all contact and induced damage Contact damage photographs should include:

234. Imprints of one vehicle on another
Friction or abrasion marks
Damage to lamps
Damage to the load
Sources of injury to pedestrians or occupants
Detailed damage to tires and wheels

235. Special Photographs
There are situations when the officer may have a specific need for a photograph which shows a unique circumstance. For example:

236. Matching Vehicle Damage
Matching vehicle damage to the road or other vehicle, matching vehicle damage to the imprint of a pedestrian’s clothing, matching imprints of a tire mark to the tire making the mark, matching imprints on the sole of a shoe to the brake or accelerator pedal, matching occupant interior contact points to the injuries on the occupant.

237. Road Situations
Features of the road at the time of the accident should be photographed. The following examples should be noted:

238. Special Photographs Road Situations Weather conditions
Traffic control devices
View obstructions
Road surface conditions

239. Photo Techniques Practice
Practice is necessary for making good pictures. The accident investigator responsible for making photographs should practice under different conditions. Charting the photographs may also help improve photographic skills.

240. Bracketing
Bracketing involves taking more than one picture of the item and changing the “f” stop one setting for each picture.

241. Fill flash
Many times a flash will provide the necessary light to fill in any shaded areas that are being photographed. Pictures taken of vehicle damage and vehicle interiors are often improved when a flash is used.

242. Overlapping photographs
Overlapping involves taking more than one photograph of a wide area. Once the pictures are developed they can be aligned so the entire area can be seen. This is particularly useful when photographing what a driver might see as he approached an intersection.

243. Photograph Identification
Numbering
It may be useful for the accident investigator to develop a system so he will know what each photograph is supposed to show.

244. Technical data
Type of camera and lens
Filters
Type of film
How the film was processed
Photographer/date/time
Chain of custody

245. Conclusion
Refine your photographic skills Having the ability to make good accident scene photographs will enhance the investigation.

246. Measuring and Diagramming Accident Vehicles
Terminal Performance Objective:
Given a simulated traffic accident, students will accurately record vehicle damage through the use of measurements and diagrams.

247. Measuring and Diagramming Accident Vehicles
Enabling Objectives:
List six measurements needed from accident vehicles
Demonstrate the process for measuring and diagramming accident vehicles

248. Introduction
Measuring and diagramming accident vehicles is becoming an important part of accident investigation. The development of sophisticated accident reconstruction computer programs has increased the need and importance of measuring damaged vehicles.

249. Measurements Needed The following measurements are needed:
Contact and induced damage
Wheelbase
Front and rear overhang
Overall length
Front and rear track
Vehicle width at the middle

250. Establish a baseline having square corners around the vehicle
Mark the points to be measured on the vehicle
List and describe the points to be measured on the measurement log sheet
Draw a field sketch
Measure from the baseline to each point using the coordinate measuring technique

251. Measuring Techniques
Record the measurements on the measurement log sheet
Record additional measurements such as wheelbase, overhang, etc on an appropriate form

252. Diagramming Techniques
Once the measuring process is complete a scale diagram can be made which will show an aerial view of the damage. A scale of 1 inch equals 2 feet is a good scale to use. Diagramming vehicles requires patience. The investigator must believe in his measurements and plot points on the paper which have been measured. Those points are then connected with straight lines.

254. Significance
The need for vehicle damage measurements is not diminished even if your agency does not have accident reconstruction computer technology. If an expert is a witness for the defense he may have the technology to reconstruct the accident by use of computer programs. On occasion these experts will make mistakes and portray a set of circumstances which are not necessarily correct.

255. If the state faces a situation of this nature they should enlist the aid of an expert who can evaluate the input data used by the defense expert. The state’s expert can also use the data collected by the on-scene investigator to substantiate the state’s case. However, if the on-scene investigator has not done a thorough job of data collection the state’s case may be compromised. The defense expert’s opinion will be more difficult to refute.

256. Conclusion
Measuring and diagramming damaged vehicles is more difficult than measuring and diagramming the road and related evidence. Measuring vehicles is not a science. It is an art. Practice is the only way to improve your skills. Do not let the difficulty prevent you from making the effort. It is your job.