Accident Investigation Tree eats car Car in the

Accident Investigation

Tree eats car…

Car in the bush…

Truck in house…

Sand buckets work…

Possible cause for single vehicle accidents

Possible Reasons 1. 2. 3. 4. 5. 6. 7. 8. *Distraction (Phone, Radio, Bugs…) Drunk Excessive speed with loss of control Slick road surface (unsafe speed, unsafe distance, bald tires) Avoidance of animal, person or other vehicle Brake/Accelerator Confusion Equipment malfunction Asleep

Process Scene • • • Photograph Draw Measure Interview Witnesses Look at vehicle documents Document weather/road conditions

Skid Marks • Evidence of braking before crash • Friction between road and tire causes burning • Can determine Minimum Traveling Speed preceding accident, site of incident, evidence of avoidance or lack of avoidance

Skid Marks-Min. Speed Simplistic SKID to STOP formula: • Assumes final velocity is 0 mph (ie. gently comes to a stop with no impact) S = speed in miles per hour (MPH), D = skid distance, in feet, and f = drag factor (includes grade considerations, braking efficiency, and coefficient of friction) f=Coefficient of Friction X Breaking Efficiency + slope

Skid Marks and Speed Vi = initial velocity, in feet per second (FPS), VE = velocity at the end of skid, in feet per second (FPS), a = acceleration/deceleration, in feet per second squared, and D = skid distance, in feet. Note: Car 1 is still traveling into Car 2 when skid marks stop

Friction Table (Estimates) • • Concrete: 0. 75 Wet Concrete: 0. 60 Dry Asphalt: 0. 65 Wet Asphalt: 0. 50 Wet Grassy Field: 0. 20 Gravel and Dirt Road: 0. 35 Ice: 0. 10 to 0. 15 Snow: 0. 20 to 0. 25

Flaws with Friction Table • Road varies in age, exact construction material, and condition • Subject’s car tire condition important

Best ways to determine real coefficient of friction • Optimal use subject car and run at known speed • Create skid marks • Calculate coefficient of friction • Or use a Drag Box

Determining a surface’s coefficient of friction • Drag Box – Box has weight – Box has tire surface on bottom of box – Measure force to pull box and maintain speed – Coefficient of friction=Avg. pull force/box weight

What if no skid marks? Explanations….

• Brake malfunction – How do disk brakes work? • • Not watching road Couldn’t see out window Drunk Unconscious

No Skid Marking • Event Data Recorder – Logs pre-crash speed – Logs brake use

No Skid Marks • Can look at Victim's Crush Depth – Depth depends on car type – About 20 in for every 35 mph V=(Vo+k)D V=Impact Speed Vo=max speed for no crush (manufacturer) K=crush stiffness (manufacturer) D=Avg. Crush Depth (measured)

Did Driver signal lane change or have headlights on?

Brake Lights

Lights • • Brake Lights have filament bowed upward This means lights were on at crash Heat and impact causes deformed shape Means that driver braked before crash

Lights Horizontal filaments tells of lights no being on at crash

NYS Traffic Law • Speeding (1 -10 MPH over posted limit): 3 points • Speeding (11 -20 MPH over posted limit): 4 points • Speeding (21 -30 MPH over posted limit): 6 points • Speeding (31 -40 MPH over posted limit): 8 points

NYS Traffic Law • Speeding (more than 40 MPH over posted limit): 11 points • Reckless driving: 5 points • Failing to stop for a school bus: 5 points • Following too closely (tailgating): 4 points • Inadequate brakes while driving an employer's vehicle: 2 points

• Failing to yield right-of-way: 3 points • Violation involving a traffic signal, stop sign, or yield sign: 3 points • Railroad-crossing violation: 3 points • Improper passing, unsafe lane change, driving left of center, or driving in wrong direction: 3 points • Leaving the scene of an incident involving property damage or injury to a domestic animal: 3 points • Safety restraint violation involving a person under 16: 3 points • Any other moving violation: 2 points

• May have your license suspended for accumulating 11 or more points within 18 months