Specialized InvestigationsSpecialized InvestigationsTraffic Accident ReconstructionWhat are some of the goals of

traffic accident reconstructions?◦Speed of vehicle◦Direction of vehicles◦Point of impact

Data CollectionData CollectionIndicators of point of impact

◦Changes in skid marks◦Gouge marks in pavement◦ Other physical damage◦Witness information

Indicators of speed◦Physical damage to vehicles◦Road surface characteristics◦Length and direction of skid marks◦Other physical damage

AccreditationAccreditationACTAR: Accreditation Commission for Traffic

Accident ReconstructionMinimum training and experience

requirements for traffic accident reconstructions

Consistency and professionalism of those involved in traffic accident investigation and reconstruction

12 participating bodiesApproximately 700 ACTAR Accredited

Reconstructionists practicing throughout the United States, Canada, Australia, Singapore and the United Arab Emirates

Second Line InvestigatorsSecond Line InvestigatorsPre-scene series of events are

those events leading up to the driver's (or pedestrian's) possible perception of the impending hazard.

The pre-scene series of events are divided into two groups: Pre-trip and Trip events.

Pre-trip EventsPre-trip EventsPre-trip events are those events

relative to the driver and vehicle occurring before the trip has started. i.e., vehicle defects, driver education, drug or alcohol use, lack of sleep, and illness.

Trip EventsTrip EventsTrip events are those events that

happen during the trip. i.e., impairment by drugs or alcohol, a stop along the way, vehicle mechanical failure, view obstructions, or sudden illness.

On-scene EventsOn-scene EventsOn-scene series of events are

those events that begin at the area of possible perception for the driver and end at vehicle separation.

Area of possible Area of possible perceptionperceptionThe place and time at which a

normal person can perceive a hazard.

SeparationSeparationThe area where the vehicles

separate and travel to final rest.

Tire Mark AnalysisTire Mark AnalysisThey are skids marks, scuffs marks,

and tire print marks: Skid marks are made by tires that

are sliding while the brakes are fully locked.

Scuff marks are made by tires that are sliding and are free to rotate.

Tire print marks are made by tires that are not sliding and are free to rotate.

Vehicle Speed EstimationVehicle Speed EstimationEngineers use two principles of physics to

determine impact speeds - conservation of momentum and conservation of energy.

If the masses of two vehicles are known and their final resting points identified, their velocities and initial directions can be determined by using vector analysis.

Skid mark analysis can be used to account for changes in velocities.

The sum of the momentums before the impact point is equal to the sum of the momentum after impact.

Vehicle Damage Vehicle Damage AssessmentAssessmentThese inspections will usually

include measuring the amount of damage and the damage profile of the vehicles.

This information is useful when an accident reconstruction is performed.

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