Accident Reconstruction for Supervisors

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					        Ok After First Aid
Comes the Accident Reconstruction
  You left me a lot of clues on how the
           events went down
• Be a “Columbo”
• Thin 5 “Ws” (Who, What, When, Where &
  Why) and “H” (How)
• Key Mission - Investigate
• Key Result – Document Evidence
                 After the police
• The second type of investigator that arrives on the scene,
  including insurance adjusters, private investigators, and
  accident reconstructionists, can still gather much useful
  evidence. Even though some evidence might be gone,
  other evidence can be gathered and used together with the
  police measurements and at-scene photographs to
  determine what happened.
• Types of evidence that can be gathered include the location
  of pre-impact skid marks, offset marks and gouge marks. If
  gathered properly, these can help the accident
  reconstructionist to determine the pre-impact direction
  and speeds of the vehicles, the types of evasive action used
  by the drivers and ultimately who was at fault in the
   a.   Overall of scene
   b.   Facing direction of vehicles approach
   c.   Area of impact
   d.   Fixed object damage
   e.   Sight distances
   f.   Sight Obstructions
   g.   Road Condition
   h.   Any evidence which you are about to secure
                          i.    points of rest of vehicles, objects, people
                          ii. tire marks
                          iii. metal scars
                          iv. debris
                          v.    fluid marks
   i. Any other conditions or items that may be of importance
The NOW Picture not the after
•   BE SAFE!
•   Coordinate with claims adjuster
•   Talk to driver
•   Inspect the scene
•   Inspect vehicles and other damaged property
•   Secure evidence
•   Talk to police not at the police
•   Talk to witnesses
•   Detail on-site claims activity
    Safety does quit because you have
              traffic vest on
• “Safety First” is the phrase that needs to occupy the thoughts of
  the investigator the entire time the investigation is being done.
  Even though this slows down the investigation, obviously it is a
  necessary component to being available for the next assignment.
  Though the scope of this paper is not to show
  methods to follow when conducting a scene investigation in a safe
  manner, it is a reminder to use proper safety methods. Remember
  the investigator is out there to gather evidence and not to cause
  another accident. When arriving at the scene be sure to park
  completely off of the roadway and as far off the
  shoulder as possible. Be visible with proper safety equipment,
  including safety vests and always be thinking “Safety First”.
Blood borne pathogens are present
• Once at the scene and after remembering “Safety First”, size up the
  scene and decide what needs to be logged and preserved. The
  physical evidence can be extremely helpful in assisting the accident
  reconstructionist in his job. This evidence includes pre-impact skid
  marks, which will show the
  direction of travel and assist in determining the speeds of the
  vehicles and offset skid marks and gouge marks, which help to show
  where the impact occurred. Other useful information includes
  scratch marks, oil or fluid spills, which can be helpful in determining
  the vehicles final rest positions. When using
  conservation of linear momentum calculations to determine vehicle
  speeds, the impact and departure angles and distances are
Look Left Look Right Look all the way
          around the Scene

Common events are:

1.   Point of possible perception B where a normally
     attentive person could have perceived the
     hazardous situation. Always comes at or before the         6.    First Harmful Event B “the first occurrence in a
     point of perception.                                             traffic accident that results in appreciable
                                                                      damage or injury; the occurrence determining
2.   Point of perception B where the (potentially)                    the time and place of the accident; usually the
     hazardous situation is actually perceived by the                 first contact in impact.”
     driver or pedestrian involved.
                                                                7.    Initial contact B the first accidental touching of
                                                                      an object collided with by a traffic unit in motion.
3.   Encroachment B is movement into the path
     assigned to another traffic unit. Example: crossing        8.    Maximum engagement B the greatest collapse
     the centerline.                                                  or overlap in a collision. The deepest
                                                                      penetration of the perimeter of the traffic unit.
4.   Start of evasive action B the first action taken by a
     traffic unit to avoid a collision course or otherwise      9.    Disengagement B separation of a traffic unit in
     avoid a hazard.                                                  motion from an object with which it has collided.

5.   Point of no escape B that place and time beyond            Note: May have repeated contacts where #7, #8,
     which the accident cannot be prevented by the                  and #9 are repeated in the second collision.
     traffic unit. The position of this point in the chain of
     events can vary considerably.                              10.    Stopping and final position B where the vehicles
                                                                      come to rest; the accident situation is
• Geometric and Traffic Regulatory Clues
   –   Geometric deficiencies
   –   Surface deficiencies
   –   Signing location and deficiencies
   –   Detail traffic control operations
   –   Street lighting location and deficiencies
   –   Construction zones
   –   Sight distances
   –   Sight obstructions
That Scene Has a Little Box that Tells
         an Amazing Story

Phase 1: Pre-Impact
  •   Ability to Make Appropriate Decision
  •   Perception / Reaction (Conspicuity)
  •   Attempt to Avoid
  •   Attempt to Stop

Phase 2: Impact

 •   Damage
 •   Injury
 •   Speed and Direction Changes
 •   “Crash Worthiness” of Objects

Phase 3: Post-Impact

 • Movement of Vehicle to Point of Rest
 • Occupant Movements / Additional Injury
 • Vehicle / Occupant “Containment”
Ok look at the Crush and Mush
• Scene Clues
  – Skid marks
  – Gouge marks
  – Points of impact
  – Debris
  – Fixed object locations and damage


   a.   Basic 4 of each unit
   b.   close ups of areas of damage to each unit
   c.    Interior
            i.    Seats
            ii. Dashboard
            iii. Gearshift
            iv. important items (alcohol, drugs, etc.)
   Look around again and again and again
          Things you would do:                                           WHY ?

1. Examine the tyres of the vehicles                Flat or damaged tyres may cause the car to lose

2. Examine the road’s condition                     Oil spill, strange obstacles and sharp objects may
                                                    cause the accident

3. Record the features of the skid marks            May show whether the tire was flat or overloading.

4. Measure the length of the skid marks             May help estimate the speed of the vehicle before

5. To know whether the drivers are drunk or         Alcohol or drug will affect a driver’s reaction time
medicated                                           during an accident.

6. Obtain the oral confession of the eyewitnesses   They can provide information which are helpful in
                                                    reconstructing the accident.

7. Examine the hazard lights of the Vehicle         To check out whether the victim had turned on the
                                                    hazard lights before the collision.

Air-Size-Tread-Scuff Marks-Stock- After Market
                                    METAL SCARS
                                           Characteristics             How They Are Made                   Accident Significance

A. Scratch                      1. Narrow                       1. With little pressure              1. Shows where a vehicle rolled
                                                                2. Sheet metal dragged across        over on the roadway
                                                                road surface                         2. Shows the path the vehicle

B. Scrape                       1. Broad                        1. With little pressure              1. Locating point of maximum
                                                                2. Underbody parts                   engagement

C. Chip Gouge                    1. A small and deep chunk of   1. By metal parts with the force     1. Made during maximum
                                pavement dug out of road        of an accident behind it             Engagement
                                surface                         2. Not just weight alone             2. Can not determine movement
                                                                                                     or direction of vehicle travel

D. Chop Gouge                   1. Broad & shallow              1. Vehicle frames                    1. Occurs at maximum
                                2. Heavy mark in bituminous     2. Transmission housing              engagement
                                material                        3. Bent wheels                       2. It can indicate the direction of
                                3. Only a scratch in Portland   4. Any metal part that is broad in   travel
                                cement (concrete)               shape and size

E. Groove Gouge                 1. Long                         1. By projecting                     1. Can/can not determine
                                2. Narrow                          a. nuts                           direction of travel
                                                                   b. studs                          2. Continues beyond point of
                                                                   c. etc.                           maximum engagement
                                                                2. Drive Shaft                       3. Can match it with the vehicle
                                                                                                     part making it
                                                                3. Broken tie rod ends

F. Towing Scratches & Grooves   Same as A, B & E above          1. Towing a vehicle from the         1. None
                                                                scene                                2. Can add confusion to the
                                                                                                     3. Should observe when vehicles
                                                                                                     are being moved
  Types of Tire Marks


 Skid     Yaw      Tire
Marks    Marks    Scrubs
Features of skid marks

                              START and STOP
The acceleration of a vehicle
Acceleration = the rate of change of the speed


          v  u  2a s
             2          2

  a = acceleration; v = final velocity; u = initial velocity; t = time interval; s = distance travelled

 Take our your drag sled do the math

To prove          F = constant x W


                                         Figure 2
       Figure 1




Drag factor f = F / W

            The braking of a vehicle

                speed  254 D f
Where speed : the speed just before sliding (measure in km/h)
      f : drag factor
      D : length of the skid mark (measure in m)

               Skid Marks
• When you brake suddenly, the wheels of your
  car lock.
• You no longer have the ability to steer.
• The car will slide straight ahead.
• Skid marks are usually straight.
• The skid mark provides evidence of the
  distance over which braking took place.
          ABS and Skid Marks
• Anti-lock brake systems (ABS) prevent locking
  and skidding by turning the brakes on and off
  several times a second.
• The driver can maintain steering control.
• Vehicles equipped with ABS may leave faint,
  intermittent skid marks.
• These skid marks may be in a curved path.
                Yaw Marks

• Yaw marks occur when a vehicle travels in a
  curved path faster than the tires can handle.
• The adhesion limit of the tires is reached, so
  they begin to slip.
• Tires “squeal” and leave marks on the
               EXAMPLES OF SKIDS

Centrifugal or Sideslid Skid

                               Yaw Skid
• Yaw marks are always
• There are often
  striations at an angle
  to the length of the
                   Tire Scrubs
• Tire scrubs are caused by a damaged or
  overloaded tire.
• They happen during or immediately after a
• Tire scrubs are usually curved and irregular in
• They may have striations at an angle.
• This picture shows a
  straight skid mark that
  changes to an irregular,
  curved tire scrub at
• The dark mark is a tire
  scrub from a second car.
         Measuring Skid Marks
• If 4 marks are found, they should be
  measured individually.

• To get the average skid distance, add the four
  measurements together and divide by four.
         Skid Marks Continued
• If three skid marks are found, add the three
  together and divide by three.

• The same applies to two marks.

• If only one mark is found, measure the entire
  length and use this as the skid distance.
               Drag Factor
• Tires slide on some road surfaces easier
  than others.
• Can you think of road conditions under
  which tires would slide easily?

What  type of road surface would be the
  hardest for tires to slide on?
       Examples of Drag Factor
• Asphalt: 0.50 to 0.90

• Gravel: 0.40 to 0.80

• Ice: 0.10 to 0.25

• Snow: 0.10 to 0.55
I.Decide if measurements are necessary
  Photograph the scene
  Locate the temporary evidence
IV.Locate and mark each point to be measured, including:
   a. Start of skid marks
   b. Skid mark direction changes
   c.   Skid mark crossings
   d. Vehicle wheel positions at first rest
   e. Gouges in the roadway
   f. Major debris points
V. Make a field sketch of the accident scene
Math is Primary ALL THE WAY!
          You Have Arrived!!
• You now have the three variables required to
  complete the minimum skid speed formula.

    S  30Dfn
S  30Dfn
  In this formula:

        S = speed in miles per hour
        30 = a constant value
        D = skid distance in feet
        f = drag factor for the road surface
        n = braking efficiency in decimal form
1.   View Obstructions                 5.   Construction Zones
                                             - Advanced warning
      - On the road                          - Cone/barrel placement
      - Off the road                         - Equipment & crew
      - Roadway contours                     - Work zone speeds
      - Intersections
                                       6.   Traffic Control
2. Reduced Visibility                        - placement
     - Darkness                              - absence
     - Fog/smoke                             - readability
     - Heavy snow or rain                    - appropriateness
     - Glare                                 Traffic Signals
                                             - Visibility
3.   Surface Conditions                      - operation sequence
       - Slipperiness                        - clearance intervals
       - Ruts
                                       7. Street Lighting
       - Holes                               - Placement
       - Curbs                               - Intensity
       - Shoulders                           - Maintenance
       - Railroad crossing
                                       8. Pedestrian/Bicycle
                                            - Facilities
4.   Road Alignment                         - Sidewalks
      - Curves                              - Crosswalks
      - Road widths
      - Bridges

•   Post accident vehicle movement
•   Point of impact
•   Skid marks /evidence of braking previous to impact
•   Human factors
•   Documents
•   Reference sources and materials
•   Statements
•   Measurements
•   Photographs
•   Calculations
•   “Standards of Knowledge”
•   Facility review
•   Operational review
                                               Drawing the Scene
Roadway Evidence
There are many types of roadway evidence that is left from a car wreck. A few of the most typical items are:
•                                                      Paint Marks left by Police
•Skid Marks
•Yaw Marks
•Tire Tracks
•Gouges in the Pavement or Dirt
•Damage to Guardrails, Barrier Walls, Telephone Poles, Curbs, Buildings, Mailboxes, and Other Structures.
•Tree Scars Indicating Impact with a Tree
•Fluid Stains such as Engine Oil, Transmission Fluid, Brake Fluid, Radiator Fluid, Blood, etc.
•Vehicle Debris from Damaged Car Parts
•Glass Fields from a Broken Windshield
•Points of Impact between Vehicles
•Final Resting Positions of Vehicles and Pedestrians
•Clothing / Shoes Worn by Pedestrians
•Cargo Separated from its Vehicle
Once you have introduced yourself you can begin building rapport. Rapport can be gained with an interviewee by
being relaxed and using a comfortable conversational style. Also it is important to be sincere and respectful
giving the interviewee the feeling that you are understanding and can be trusted.
After establishing a reasonable degree of rapport you can begin to move into the questioning phase of the
interview. It is important to remember that rapport is built and maintained throughout the interview not just at
the beginning. Therefore it is important to continue to be professional and somewhat relaxed during the entirety
of the interview. That said, the interviewer should maintain a balance realizing the need to maintain control of
the discussion and keep focused and on track.
Some tips to remember before beginning:
• take your time
• allow periods of silence where necessary
• avoid compound questions
• stay neutral, professional, and unbiased
• do not make assumptions or jump to conclusions
• do not interrupt
• questions should start out general and move to specific
• try not to use leading or loaded questions
• avoid accusatory questions or statements
• don’t argue or debate
Defects in the design or construction of a
highway can create hazardous conditions that
lead to accidents.

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