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 Common methods used to determine speed in a collision:

1. Skid Marks




                        Roadway Grade

            -Results: Minimum Speed

2. Time Distance


                        Distance Vehicle Traveled

                        Velocity/ Speed Conversion Factor - Speed x 1.466 = Velocity, Virginia Code 46.2-880

                        Suspected Speed Results


                        Actual Speed

                        Avoidability Issues

                        Witness Credibility

3. Yaw Marks





            -Results: Actual Speed

4. Momentum


                        Vehicular Gross Weights

                        Approach Angles

                        Departure Angles

                        Post Impact Speeds (Skid Formula)

            -Results: Accurate speed estimates at impact

5. Fall, Flip, Vault


                        Point of Impact

                        Point of Final Rest

                        Distance Airborne

                        Departure Angle

                        Roadway Friction

            -Results: Accurate speed determination at the time of the event

6. Collision Damage


                        Depth of Engagement

                        Width of Engagement

                        Manufacturer's Crush Specifications

            -Results: Very accurate speed at impact

7. Crash Data Retrieval System & Infortainment System Downloads


                        1990 - 1997 GM Vehicles- limited data

                        1998 - forward GM Vehicles- all data

                        2000 - forward, all vehicle research and development

                        2015 - ALL Vehicles required by law

            -Results: Computer Download Information

                        Type I

                                    Near Deployment Event

                                    Air Bag Does Not Deploy

                                    Event Stored Until Ignition Cycled 250 Times

                        Type 2

                                    Deployment Event

                                    Pre Crash and Crash Data

                                    Cannot Be Erased


                                    Velocity Change (DeltaV)

                                    Vehicular Speed

                                    Brake Switch Circuit Status

                                    Driver Seat Belt Circuit Switch Status

                                    Passenger Front Airbag Suppression Switch Status                                   

                                    Time Evaluations


Accident Investigation Tips

  • Take prompt action - inspect the site immediately.
  • Save and protect any evidence that could be critical later...take LOTS of pictures both close and far.
  • Do not disturb the accident site unless it presents a hazard. Give yourself time to inspect and analyze your findings.
  • Take photographs and measurements. Document pertinent serial numbers, manufacturer and model names.
  • Analyze your findings - study possible causes of the accident, including unsafe conditions or practices.
  • Ongoing training must be an important part of your safety plan.

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