ACTAR Collision Analysis & Reconstruction 3 — Questions and Answers
Question 1: A reconstructionist uses the 'CRASH3' program or similar stiffness-based model. What does the stiffness coefficient 'B' represent?
- The force required to initiate any crush
- The rate of force increase per unit of additional crush depth (Correct answer)
- The vehicle's total weight
- The post-collision rebound velocity
Correct answer: The rate of force increase per unit of additional crush depth
The stiffness coefficient B represents the slope of the force-crush relationship — how much additional force is required per additional unit of crush.
Question 2: In a rollover reconstruction, which energy source is analyzed to estimate minimum vault speed?
- Tire deformation energy
- Potential energy gained during roll
- Kinetic energy at the initiation point (Correct answer)
- Air drag energy over the vault distance
Correct answer: Kinetic energy at the initiation point
The kinetic energy at roll initiation is analyzed, often using vault distance and height to back-calculate minimum pre-rollover speed.
Question 3: What does 'PDOF' stand for in the context of collision reconstruction?
- Post-Dynamic Offset Factor
- Principal Direction of Force (Correct answer)
- Pre-Deformation Offset Function
- Point of Departure from Original Friction
Correct answer: Principal Direction of Force
PDOF — Principal Direction of Force — describes the resultant direction of the impact force applied to the vehicle.
Question 4: When analyzing a head-on collision between two vehicles of very different masses, which vehicle typically experiences the greater velocity change (delta-V)?
- The heavier vehicle
- The lighter vehicle (Correct answer)
- Both experience equal delta-V
- The vehicle traveling at higher speed
Correct answer: The lighter vehicle
By Newton's third law, the impulse is equal and opposite, so the lighter vehicle undergoes a greater velocity change (delta-V) because delta-V = impulse / mass.
Question 5: In the context of roadway evidence, what information do 'gouge marks' primarily provide to reconstructionists?
- Vehicle speed before braking
- Point of maximum engagement or the area of contact between vehicles (Correct answer)
- Post-impact travel direction
- Road surface drag factor
Correct answer: Point of maximum engagement or the area of contact between vehicles
Gouge marks are created when hard vehicle components contact the road surface and typically indicate the area of maximum engagement or point of impact.
Question 6: For a vehicle traveling on a banked curve, how does superelevation affect the effective drag factor used in critical-speed calculations?
- Superelevation has no effect on the drag factor
- It increases effective drag on the high side and decreases it on the low side (Correct answer)
- It always decreases the effective drag factor
- It always increases the effective drag factor
Correct answer: It increases effective drag on the high side and decreases it on the low side
The roadway bank (superelevation) adds or subtracts from the lateral friction available, depending on which side of the curve the vehicle is sliding.
Question 7: A vehicle's EDR (Event Data Recorder) shows a recorded speed of 55 mph at 1 second before impact. What must a reconstructionist verify before using this data?
- Whether the vehicle had cruise control engaged
- The data's accuracy, calibration, and whether the sensor was functioning properly (Correct answer)
- The driver's license status at the time
- The vehicle's insurance coverage
Correct answer: The data's accuracy, calibration, and whether the sensor was functioning properly
EDR data must be validated through proper download protocols and cross-checked against physical evidence to confirm accuracy and sensor integrity.
ACTAR Collision Analysis & Reconstruction 3
A reconstructionist uses the 'CRASH3' program or similar stiffness-based model.
What does the stiffness coefficient 'B' represent?