11. Accident Investigation

11. Accident Investigation road/"https://pittsburgh.cbslocal.com/2019/08/05/route Accident Investigation pioneer When is an Accident Investigated? • Fatality, Injury, Alcohol related, Crime related, Unusual circumstances, Large amounts of damage. Required Skills • Math, Physics, Common Sense, Analytical Skills, Experience Basic Concepts • An object in motion will stay in motion unless acted upon by an outside force. • The faster you are traveling, the longer it will take to stop. • Alcohol slows down reaction time. • Slick roads reduce the coefficient of friction. • Driving a motorcycle into a car hurts. Mph to F/S Determining Vehicle Speed Skid marks, Damage to car & surrounding area, Injuries, debris trail, Speedometer “pinning.” • 30 mph = 44 f/s • 60 mph = 88 f/s • 100 mph = 146 f/s A F = Drag Factor for Road Surface Reaction Time N = Braking Efficiency (%) • The average person takes 3/4 second to react in an emergency. • This means if you are going… • 30 mph, you will travel 33 feet before you hit the brakes. • 60 mph, you will travel 66 feet before you hit the brakes. • 100 mph, you will travel 109 feet before you hit the brakes. How Do We Know What Happened? • Location of vehicle(s), injuries, seat belts, cell phones, weather, driver & witness accounts. S = √(30DFN) • S = Speed (mph) • D = Skid Distance (Decimal, Feet) Brakes • Each wheel on a car provides a certain amount of the total brake force available. • If all 4 wheels are braking evenly, leaving 4 distinct skid marks, braking efficiency is 100%. • If the Rear brakes are not functioning at all, then 40% of the brake force is not available. • For rear wheel drive cars, the brake force can be assumed to be 30% for each of the front wheels and 20% for each of the rear wheels. Air Bag & Black Box Crash Data Available (Depending on Year & Model) 1. Vehicle Speed (in 5 1-second intervals preceding the impact) 2. Engine Speed (in 5 1-second intervals preceding the impact) 3. Brake Status (in 5 1-second intervals preceding the impact) 4. Throttle Position (in 5 1-second intervals preceding the impact) 5. Driver Seat Belt State (on/off) 6. Passenger Airbag State (on/off) 7. Airbag Warning Lamp Status (on/off) 8. Time from Vehicle Impact to Airbag Deployment 9. Maximum Delta-V (DV) for Near-Deployment Event 10. DV vs Time for Frontal Airbag Deployment Event 11. Time from Vehicle Impact to Time of Maximum DV 12. Time Between Near-Deploy and Deploy Event (if within 5 seconds) Additional Crash Data (2006 & Newer GM Vehicles) 1. Low Tire Pressure Warning System Status 2. Traction Control Status 3. Anti Lock Brake Status 4. Transmission Range 5. Service Engine Lamp Status 6. Vehicle Door 2/4 Status (Open/Closed) 7. Outside Air Temperature (ºF) 8. Passenger Seat Belt Switch 9. Yaw Rate 10. Lateral Acceleration 11. Steering Wheel Angle 12. Principle Direction of Force Degrees (PDOF)