Vehicle Mishap Investigation Handbook: Basics and Practice

1. MINA Handbook Chapter 10: Vehicle Mishap Investigation

2. Investigating Vehicle Mishaps Private Motor Vehicles Motorcycles Government Motor Vehicles

3. Basics - Inertia • Inertia • Momentum is inertia in motion • Property of matter that causes it to resist change in its motion • A body at rest wants to remain at rest • A body in motion wants to remain in motion

4. Basics - Momentum • Force Force x Time = Impulse = Mass x (change in) Velocity An impulse changes an object’s momentum

5. Momentum • If I have an 80,000 kilogram truck moving at 2mph and a 2,000 kilogram pickup truck moving at 80 mph, which one has the most momentum? Momentum = mass X velocity 80,000* x 2 = 160,000 2,000* x 80 = 160,000 *should use Kg for mass

6. Effect of Kinetic Energy

7. The Haddon Matrix

8. The Police “Cause” of the Accident and Safety • For the police officer, it is convenient to match a law violation with a “cause” but this practice tends to ignore other existing factors that may have been present and were equally contributing to the accident. • By the time the officer investigator gets to the physical evidence it may have been disturbed, swept away, or washed down. The scene has lost its integrity. • Safety investigations need to get beyond the typical police investigation that fills out a form and looks for a law violation. • But how does a safety investigator prepare for a vehicle accident investigation?

9. Practice, Practice, Practice • Get in the habit: • Be specific • Evaluate what people say • Make personal observations • Write down information at the time • At every step, think about the data you are collecting • Get the facts and avoid “I’ll get that later” • Practice is as necessary for vehicle accident investigation as it is for combat arms or first aid. • Perform skid tests • Question skid marks on base road surfaces • Practice placing chalk marks • Practice measuring • Practice field sketches • Practice photography • Visit an automobile “graveyard”

10. Investigation Guides MINA TEXT APPENDIX 4

11. THE FACTORS OF A MISHAP People Vehicles Environment

12. Look for Multiple Factors For example, in a two car head-on collision, multiple factors come into focus. Ask questions. Why was one driver left of center? Was it a problem of perception? Or Attitude? Was a driver distracted? Why didn’t the other driver take evasive action? Why was one driver injured and the other not? Were the vehicles in good mechanical condition? Were seat belts and airbags installed and did they work? Did the vehicle provide “living space” to the occupants during the crash sequence? Is there a road design defect? A failure to properly mark, sign, or maintain the road? Was there a distraction along the road?

13. Humans • Positions – “normal” seating? • Seatbelt use – airbag selection, deployment • Physical handicaps – eyesight, hearing, etc • Distractions – kids, pets, cell phones, eating, drinking coffee/sodas, critters, etc. • Impairment – alcohol, drugs, CO, fatigue, etc • Attitudes - approach to driving, habits • Road Rage – reaction to incidents • Witnesses at a traffic accident scene or indirect witnesses • Responders – knowledge, skill, training, other • Injuries – aggravated or mitigated? • Three crashes in a vehicle accident

14. Traffic Accident Witnesses • Don’t ask. “Did you witness this?” “Witness” turns people off. • Ask. “What happened here?” or “Which way did this car come from?” • If they give you a written statement, don’t say “Sign this.” They’ll get defensive. • Say. “Thank you. I’ll go over this later. In case I can’t make something out, give me a phone number at the bottom so I’ll know who to call.”

15. Human Error in Traffic Accidents • Study found human error the sole cause in 57% of all accidents and contributing factor in over 90%. • Only 2.4% were due sole to mechanical fault and only 4.7% were causes only by environmental factors.

16. THE ENVIRONMENT

17. Environment Important Terms of the Road • GRADE The uphill or downhill incline of the road surface • CROWN Construction of the road with the center higher than the outside to assist in water runoff. • SUPERELEVATION The bank of a curve. It may be positive or negative

18. Environment • Weather conditions – fog, rain, ice, snow, etc., other visual impediments: night, smoke, etc. • Pavement type & condition • Traffic control devices • Objects on or near roadside • Obstructions to visibility • First contact point

19. Information from Roads • Pavement type & condition • Evaluate the entire traffic way – road, shoulder and roadside • Tire marks • Tire/Road surface drag factor – coefficient of friction (u) • Scars on road, shoulders • Debris – gravel, “normal debris” • Traffic controls devices, do they relate to the actual surface conditions? • Skid marks, scuff marks, yaw marks

20. Coefficient of Friction (u) • Force required to move a vehicle at a constant speed over the surface divided by the weight of the vehicle. • Sources for u • Charts • Traffic engineers • Drag sleds • Skid tests – using an exemplar vehicle

21. Common Variables That Affect Coefficient of Friction (u) • Size of Tire-Pavement contact patch (footprint) • Weight • Vehicle type • Temperature • Speed • Tires

23. Measuring Skid Marks Objective: To determine how far the vehicle’s center of mass skidded. A skid mark is a tire mark on a road surface produced by a tire that is locked, not rotating. There are other marks made by tires: scuffs, scrubs and yaw marks. NOTE: To arrive at a center of mass distance you must sometimes add or subtract wheel base length or gap length to actual tire mark length. NOTE: To measure skid marks, you must know the drag factor of the vehicle and the distance the vehicle skidded.

24. Straight Overlap Skid Marks • Rear tires should track directly behind the front tires leaving only left and right skid marks. • If it cannot be determined where the front wheel skid marks begin due to being overridden by the rear wheel skid marks, measure the entire length of the two skid marks, subtract one-half of the wheelbase of the vehicle from the total and divide by two. The result is the average skid distance.

25. Straight Overlap Skid Marks • Rear tires track directly behind the front tires leaving only left and right skid marks. • If it cannot be determined where the front wheel skid marks begin due to being overridden by the rear wheel skid marks, measure the entire length of the two skid marks, subtract one-half of the wheelbase of the vehicle from the total and divide by two. The result is the average skid distance.

26. Straight Offset Skid Marks • All four wheels may leave a separate skid mark. • Use either longest, shortest or average of skid marks as center of mass distance travel

27. Gap Skid Marks • Most commonly from anti-lock brakes • If the gap is shorter than the wheel base (anti-lock system) Measure the entire length of the skid including the gap. • If the gap is longer than the wheel base treat each as a separate skid

28. Skip Skid Marks Usually distinguished by small breaks, no more than 1-2 feet long that repeatedly and regularly interrupt the skid mark. Bouncing rear wheels of semi-trailers are the most common source. Measure from beginning to end of the entire skid mark including breaks.

29. Measuring Skid Marks • The skid marks in a skid test are often not the same length. Which do you use? • Using the longest skid mark produces the lowest u which will decrease the speed computed from skid marks at the mishap scene. • Using the shortest skid mark from the skid test produces the highest u which will increase the speed computed from skid marks at the mishap scene. • Averaging the lengths will produce a u somewhere in-between.

30. Vehicle Speed From Skid Marks • Equation • Table • Nomograph • Template

31. Vehicle Speed From Skid Marks • When length of skid marks, pavement coefficient of friction and grade are known, you can calculate the vehicle’s minimum speed at the point it began to skid. • This is NOT speed at impact Where S = speed in MPH D = skid distance of center of mass, in feet F = coefficient of friction on the road surface G = grade of the road surface Uphill is + Downhill is -

35. Difficulties - Measuring a Yaw Mark • If the calculated speeds do not decrease from beginning through midpoint to the end, you have made an error or some other factor such as acceleration is involved – Do not try to calculate speed from yaw. • A significant change in striation appearance indicates that the forces acting on the vehicle have changed (vehicle was hit, hit something. Brakes have locked, etc.) The yaw mark segment after the change should not be used in calculation. • Don’t use yaw marks when significant weight shift occurs – high center of mass vehicles (SUV’s) • All four wheels must be on the same pavement for calculations to be valid. • Yaw marks after a collision as affected by the physics of the collision – Do not use for calculations.

36. Vehicles • Condition and repair status • Positions • Scratches & scrapes, impact marks (capture) • Debris • Lights (bulb analysis) • Computer chips • Pedal imprints on shoe soles • Tissue of hair on windshield, steering wheel, etc. • Glass condition

37. Determining Seat Belt Use • Need to understand the dynamics of the collision • Need to understand the direction of forces applied • Need to understand the restraint system’s capabilities • Always wear gloves when examining seat belts and vehicles interiors

38. Determining Seat Belt Use • First, visually inspect the vehicle interior in a direction opposite the PDOF • Perform a visual check of the belt system • Does it look as though it is frequently worn? • Were they pushed beneath the seats? • Is there any fraying? • Stains or markings on the webbing? • Compare the feel of the belt with other belts in the vehicle • Look for shiny surfaces on the webbing • Look for buckling or puckering in the webbing • Rapid payout of webbing may generate heat • Is the belt cut?

39. Determining Seat Belt Use • Determine the length of the belt in use. • Slip the latch plate into the buckle. Listen for it to “click”, tug on it to see if it comes out of the buckle. Check the release. • Check the attachment points. • Activate the retractor by giving the belt a sharp tug – or some automobiles have vehicle sensitive retractors.

40. Determining Seat Belt Use

41. Problem Seatbelts

42. Vehicle Damage

45. Motorcycles • Estimating Vault Distance and Speed • Angle of ejection • 45 degrees is often used to estimate a minimum speed • A vault over a hood of a car can be much lower, around 5 or 6 • Distance cyclist is airborne • Distance cyclist slides after ground contact • Drag factor: cyclist contacts ground at same horizontal speed that was ejected. Drag factor is figured after ground contact to FRP when cyclist is tumbling or sliding.

46. Center of Gravity

47. Remote Condition Factors Remote condition factors may be considered when dealing with cause analysis although they are seldom of significance to the investigator on a single accident case. • Moral influences, religion, beliefs, legal influence and values on vehicle designers, highway engineers, drivers and pedestrians. • Operating a vehicle in another region of the world that has different laws, rules (formal and informal), values, highway construction, maintenance and signage.

48. Data Recovery Systems • In the 1970’s, electronically controlled fuel injected engines gained wide use in production automobiles. • New electronic systems found their way into the automobile • Acceleration sensors for airbag modules • Wheel speed sensors for ABS and Traction Control • Vehicle yaw rate sensors for Stability Control • 1970’s, NTSB recommended using onboard collision sensing and recording devices to gather information on vehicle crashes.

49. Data Recovery Systems • In 1992, crash-data recorders were installed on 70 Indy race cars. • Capability to record pre-crash data began in 1999. • Typically records last 5 seconds of data immediately prior to enabling the algorithm. • Vehicle speed, engine speed (RPM), throttle position, brake switch, driver’s seat belt status, passenger’s airbag selection switch status