ACTAR Crash Dynamics 4 — Questions and Answers
Question 1: What does the term 'delta-V' represent in vehicle collision analysis?
- The change in velocity experienced by a vehicle during the collision event (Correct answer)
- The difference in speeds between two vehicles before impact
- The peak deceleration force on an occupant
- The closing speed at time of impact
Correct answer: The change in velocity experienced by a vehicle during the collision event
Delta-V is the vector change in velocity a vehicle undergoes during the impact phase, a key metric for severity assessment and occupant injury evaluation.
Question 2: When a vehicle understeers during a pre-crash avoidance maneuver, the front tires are operating:
- Below their lateral force capacity
- At or beyond their lateral force capacity, causing the vehicle to push wide (Correct answer)
- In a regenerative braking mode
- With excess camber thrust
Correct answer: At or beyond their lateral force capacity, causing the vehicle to push wide
Understeer occurs when front tire lateral forces are saturated, causing the vehicle to follow a path with a larger radius than the steering input commands.
Question 3: In the context of a side-impact collision, the 'struck side stiffness' is generally lower than frontal stiffness because:
- Side impacts are always lower speed
- Vehicle door structures lack the longitudinal frame rails present at the front and rear (Correct answer)
- Side airbags absorb all energy
- Tires on the struck side act as energy absorbers
Correct answer: Vehicle door structures lack the longitudinal frame rails present at the front and rear
Vehicle doors and side panels lack the strong longitudinal frame rails and crumple zone design present at the front, making them structurally less stiff and leading to greater intrusion per unit energy.
Question 4: Which of the following conditions would cause an analyst to OVERESTIMATE pre-impact speed when using skid mark analysis?
- Using a drag factor that is too high
- Using a drag factor that is too low (Correct answer)
- Measuring skid marks as longer than actual
- Ignoring grade correction on a downhill road
Correct answer: Using a drag factor that is too low
Using a drag factor that is too low underestimates the decelerating force, requiring a higher computed speed to produce the observed skid length, thus overestimating speed.
Question 5: A vehicle traveling uphill on a grade of 5% has an effective drag factor that is:
- Increased by 0.05 compared to level road (Correct answer)
- Decreased by 0.05 compared to level road
- Unchanged because grade only affects stopping distance
- Doubled due to gravitational resistance
Correct answer: Increased by 0.05 compared to level road
On an uphill grade, gravity adds resistance to braking, so the effective drag factor increases by the grade value (expressed as a decimal), e.g., f_eff = f + 0.05.
Question 6: The term 'closing speed' in a collision context refers to:
- The speed of the faster vehicle alone
- The rate at which the distance between two approaching vehicles decreases (Correct answer)
- The post-impact speed of both vehicles combined
- The speed at which airbags deploy
Correct answer: The rate at which the distance between two approaching vehicles decreases
Closing speed is the scalar sum of the components of each vehicle's velocity directed toward the other, representing how quickly the gap between them closes.
Question 7: In an energy-based reconstruction of a collision, which measurement of crush depth is considered the most critical input for accurate delta-V estimation?
- Maximum crush depth at the point of greatest deformation
- Average crush depth across the damage profile (Correct answer)
- Crush depth at the vehicle centerline only
- Depth of the deepest single point of intrusion
Correct answer: Average crush depth across the damage profile
The Campbell model uses the average of multiple crush measurements across the damage zone to represent energy absorbed, making the average crush profile the most critical input.
ACTAR Crash Dynamics 4
What does the term 'delta-V' represent in vehicle collision analysis?