Biomechanical Injury Criteria:  A calculated value (or “score”) corresponding to the general (i.e., population-based) risk of injury to a certain body part, based on the severity and/or duration of forces experienced by that body part during an incident. 

Bobtail:  A tractor truck without a trailer. 

Center of Gravity:  The point at which the entire weight of a body may be considered as concentrated so that if supported at this point the body would remain in equilibrium in any position. Theoretical point that often is used for analysis through which all mass acts. 

Coefficient of Friction:  A number representing the resistance to sliding of two surfaces in contact. 1 

Coefficient of Restitution (e):  A measure of how much rebound occurs during an impact, ranging from 0 to 1. For example, e = 0 means the impact is perfectly “plastic” or “sticky” (the objects do not separate after impact), whereas e = 1 means the impact is perfectly “elastic” (picture two billiards balls colliding). 

Collision Deformation Classification: A classification of the extent of vehicle deformation as per SAEJ224 (Society of Automotive Engineers J Standard). 

Conservation of Energy:  The principle of physics stating that the amount of energy in a closed system is constant regardless of the changes in the form of that energy. 1 

Conservation of Momentum:  Regarding vehicles, the principle of physics that the sum of all vehicle before-collision momentum must equal the sum of all vehicle after-collision momentum. 1 

Contact Damage:  Damage to the vehicle caused by direct contact with another object.  

Crash Pulse:  The measured acceleration curve of a vehicle during the duration of a crash. 

Critical Velocity:  A velocity above which a particular highway curve, or a curve encountered by a driver, could not be negotiated by a motor vehicle without exceeding the available traction force at the tires on a specific surface. 1 

Crush Profile:  The geometric shape in a specified plane which describes the vehicle damage resulting from an impact. 1 

Delta V:  The change in velocity that results at a vehicle’s center of mass during a collision. This term is often used in accident reconstruction to quantify the severity of a crash.  

Design Controls for Medical Devices:  This phrase refers generally to a set of practices intended to ensure that finished devices meet product requirements. More specifically, this term refers to the requirements put forth in 21 CFR part 820.30, which are enforced by the FDA. This regulation mandates, for non-excepted devices, the creation of key documents in the development cycle such as Design Input, Design Output, Design V&V, Design Reviews, Change Management, and Design History File. 

Drag Factor:  A number representing the acceleration or deceleration of a vehicle or other body as a decimal fraction of the acceleration of gravity. 1 

Drive Terminal:  The location of a chairlift's primary braking system, which can be located at the top or bottom of an installation. 

Exemplar:  An example or unblemished model. For example, the reconstructionist often utilizes exemplar vehicles that resemble the subject vehicle before it was damaged in a crash.  

Failure Modes and Effects Analysis:  A detailed, proactive brainstorming of the ways or modes in which a failure could occur and the subsequent consequences, or effects, or such failures. For bio/medical products, FMEA is typically done both for product design (Design FMEA) or processes like manufacturing and testing (Process FMEA). 

Friction:  The resisting force to motion between two surfaces at their interface (contact). 1 

Induced Damage:  Damage to a vehicle that is a result of a crash but not a direct result of the impact with another object or vehicle. Also referred to as indirect damage. 

Lift Attendant:  A person who is responsible for the supervision and control of persons travelling up and down chairlifts. 

Lift Operator:  A person who is responsible for the operation of a chairlift including starting, stopping, and adjusting speed. 

Maximum Engagement:  Greatest penetration of one body, such as a vehicle, by another during a collision, which is the instant of greatest force between colliding objects.   

Mechanism of Injury:  The specific transfer of forces, moments, or energy to specific human tissues resulting in a mechanical overload exceeding the physical strength of the tissue (i.e. injury). 

Micromobility Device:  A range of small, lightweight vehicles such as bicycles, skateboards, and scooters (including the electric versions) that are driven by users. 

Occupant Kinematics:  How the occupants of a motor vehicle move within the vehicle during a collision. Occupant kinematics analysis is based on the dynamics of the crash, human biomechanics, seat belt loading marks, and other evidence of vehicle/occupant interaction. 

Overhang:  The longitudinal distance from the center of the front/rear axle to the foremost/rearmost point on the vehicle. 

Oversteer:  A characteristic of a motor vehicle that results in a tendency to turn more sharply than is intended by the driver. 

Pedelec:  Another name for an electric bike. 

Perception-Response Time:  The time necessary for a driver to recognize an easily identifiable hazard and enact a measurable response.  

Photogrammetry:  The science of producing reliable measurements through the use of photographs that contain usable evidence of a given crash or event. 

Pitch:  Rotation around the lateral axis of the vehicle. 

Principal Direction of Force (PDOF):  The total of the collision forces expressed as one resultant force; the summation of those forces over the contact duration expressed as a resultant vector. 1 PDOF is typically represented as an angle (degrees), or hours on a clock dial. For example, a front-to-rear impact has a PDOF of 12 o’clock, or 0 degrees. A perpendicular right-to-left impact has a PDOF of 3 o’clock, or +90 degrees. A rear-to-front impact has a PDOF of 6 o’clock, or 180 degrees. A perpendicular left-to-right impact has a PDOF of 9 o’clock, or -90 degrees. 

Return Terminal:  The terminal of a chairlift that is not the drive terminal. 

Roll:  Rotation around the longitudinal axis of the vehicle. 

Scuff Mark:  A tire friction mark made by a tire that is both rotating and slipping on a road or other surface. 1 

Skid Mark:  A friction mark on a pavement made by a tire that is sliding without rotation. 1 

Slip Angle:  The angle between the direction a vehicle is traveling and the front-to-rear axis of the vehicle.  

Tire Friction Mark:  A mark made when a slipping or sliding tire rubs the surface of the road or another surface. 1 

Understeer:  A characteristic of a motor vehicle that results in a tendency to turn less sharply than is intended by the driver. 

V&V:  Verification and Validation. These are procedures employed to check that a product meets requirements and fulfills its intended purpose. Verification refers to procedures that verify (e.g., check a result against a requirement) a specification, whereas validation is the establishment of objective evidence with a high degree of certainty that a requirement has been met. 

Wheel Slip:  The ratio of the forward velocity of the tire at the road surface to the forward velocity at the center of the wheel. 1 

Wheelbase:  The longitudinal distance from the center of the front axle to the center of the rear axle.  

Yaw:  Rotation around the vertical axis of the vehicle.  

Yaw Mark:  A scuff mark made while a vehicle is yawing; the mark made on the road by a rotating tire that is slipping in a direction that is parallel to the axle of the wheel. 1 

1 Fricke, Lynn B. Traffic Crash Reconstruction, 2nd ed. Northwestern Center for Public Safety, 2010.