John Fiske Brown Associates, Inc.

    ACCIDENT RECONSTRUCTION DEFINITIONS

 

ABS (antilock braking system): Computer intervention to interrupt skidding momentarily for improved control simultaneous with maximum brake performance.

Acceleration: Rate of change in velocity with respect to time.

Acceleration Skid: Tire mark left due to hard acceleration, “burn-out” (informal).

Accident Reconstruction: The art and science of using engineering principals to determine what really happened in an anomalous event.

Accident: An unintended event with a negative outcome.

Backlite:  The rear-facing window of a car, sometimes called the rear windshield.

Baker, J. Stannard: The pioneer of accident reconstruction.

Barrier Equivalent Speed: The speed at which the same vehicle would have to hit a fixed rigid barrier to sustain the same magnitude of damage.

Bead: The reinforced part of a tire that engages the rim.

Biomechanics: The application of engineering mechanics to a biological system, especially the human body.

Bobtail: A short truck without a trailer, specifically a truck tractor with no trailer.

Braking Skid:  Tire mark left due to hard braking.

Cab: The driver's compartment of a truck, not an entire vehicle (see tractor).

Closing Speed: The speed of one vehicle relative to another without regard to actual speed relative to the ground.

Crash Speed: An ambiguous term to be avoided.

Centrifugal Force:  Radial force acting on a vehicle while turning or negotiating a curve.

Centrifugal Skids:  Tire marks left from a vehicle turning at critical speed (see Yaw Marks).

Critical Speed: Speed at which the centrifugal force of a vehicle negotiating a curve exceeds the traction force of the tires on the road.

Crush:  Permanent damage or deformation sustained by a vehicle as a result of impact.

Deceleration: Negative acceleration.

Delta:  Δ (Greek), Difference or change.

Delta-V: (ΔV) Change in velocity, may be cited in miles per hour (mph) or feet per second (fps).

Duals: Two tires at one wheel position.

Eighteen-wheeler: A maximum legal size truck, usually having 18 tires on 5 axles.

g: Universal gravitational constant; for Earth, 32.2 feet per second per second.

GAWR: Gross axle weight rating, the maximum total weight to be applied to the ground by that axle.

GVWR: Gross vehicle weight rating, the maximum total weight the vehicle is designed to apply to the ground.

Human Factors: The study of the interaction of humans with their working environment.

Hydraulic: Using moving fluid (liquid) that is pressurized to do work.

Hydroplane: To be supported by the surface of water by traveling at high speed.

Impact Speed: Closing speed at impact (see closing speed).

Lay it down: To deliberately cause a moving motorcycle to be upset onto its side.

OEM: Original Equipment Manufacturer.

Momentum:  Mass or weight times velocity or speed.

Pressure: Force distributed over area.

Prolongation of a line: Poorly defined term used in traffic accident reports.  It may be the true prolongation, a perpendicular offset to a point of tangency, or a figment of someone’s imagination.

Quarter Panel: The sheet metal surrounding the rear wheel area of a car or pickup.

Tractor: A truck built specially to pull a semi-trailer.

Turning Circle: Diameter of the minimum circle within which a vehicle can physically fit during a turn (a design specification).

V: Generally designates Velocity.

Vector: A mathematical quantity having both a magnitude and direction.

Velocity: Speed in a specified direction.  In accident reconstruction velocity is usually expressed in feet per second and speed in miles per hour.  Speed, if expressed in feet per second, may be called (incorrectly) velocity.

Yaw mark: Tire mark made by a tire that is side-slipping during a high-speed turn (see Centrifugal Skids and Critical Speed).