ABS Antilock brake system.
Acceleration The second derivative of position with respect to time (the first being velocity). The change in velocity with respect to time. It is expressed in feet per second (fps) squared, meters per second (m/s) squared or the more familiar gravitational unit, g. 1 g is equal to 32.2 fps2 or 9.81 m/s2. Peak acceleration is a measure of the highest recorded acceleration amplitude. Mean acceleration is nearly always less than the peak and is the average acceleration over the duration of the event (total change in velocity divided by the duration).
Acceleration-time history A plot of the acceleration of a body or object (which is usually on the y axis) over time (which is usually on the x axis).
Aggressivity The measure of the aggressiveness of a vehicle in terms of the potential damage it inflicts upon its crash partner, or the potential for injury or death of the crash partner’s occupants; aggessivity=fatalities in collision partner/number of crashes of subject vehicle.
AIS Abbreviated injury scale.
ATD Anthropometric test device (or dummy).
Backset The distance between the back of the head and the front of the head restraint.
BEV Barrier equivalent velocity (see also equivalent barrier speed (EBS) and equivalent energy speed (EES)); a value calculated using empirically-derived energy formulae which are based on the results of vehicle-to-rigid-barrier crash tests and the resulting residual crush; this calculated value—depending on the characteristics of the subject crash—can be equal to, less than, or greater than the vehicle’s actual delta V.
Bullet vehicle The vehicle that strikes another vehicle.
CAD Cervical acceleration/deceleration (the kind of force-induced kinematic response occurring in the occupants of rear-struck vehicles).
CAFE Corporate average fuel economy; an average economy required by the government of all auto manufacturers. It is in constant flux, changing by government decree and there are standards for passenger cars and light trucks, vans, and SUVs.
CDS Crash worthiness data system.
Cervical spine distortion A common German term for whiplash.
Change of velocity Also known as delta V, it is the difference between a vehicle's pre-impact velocity and its post-impact velocity. It is considered one of the more important crash parameters in terms of understanding injury risk in all collisions.
Closing velocity This term defines the differential velocity between two crash partners and is more meaningful than impact velocity for the purposes of considering injury risk.
Compression Opposite of tensile stress. A downward force on the head, for example, would result in axial compression of the spine.
Covariant When variables tend to vary with each other and are not strictly independent. Shoe size and weight are covariable. Age and the number of health practitioner visits are covariable.
Crash partner The other vehicle one crashes with.
Crash pulse Usually the acceleration-time history of a crash.
Crashworthiness The ability of a vehicle to protect its occupants in a crash.
DAI Diffuse Axonal Injury.
DOT Department of Transportation.
Dynamic crush The total amount of structural crush occurring in a crash; due to the elasticity of steel, this measurement will generally be higher than the residual crush; at maximal dynamic crush, colliding cars have no relative velocity (inertial forces at the interface are zero).
EBS Equivalent barrier speed (see BEV).
EDR Event data recorder.
EES Equivalent energy speed (see BEV).
Elastic modulus The ratio of the increment of some form of stress to the increment of some specified form of strain (e.g., Young's modulus, shear modulus, etc.). Also known as the coefficient of elasticity.
EMG Electromyogram.
Far side impact A side impact in which the occupant is struck on the side opposite them (e.g., a driver is struck from the passenger's side).
FARS Fatal automotive reporting system.
FMVSS Federal Motor Vehicle Safety Standard.
fps Feet per second.
GCS Glasgow Coma Scale; a scale of 1-15 in which 15 is a perfect score.
Head lag The rearward motion of the head relative to the torso during the first phase of whiplash.
Head overspeed Increased speed over that of the torso during the forward phase of CAD; due primarily to the kinematic effect of the head's rearward phase combined with the head restraint's coefficient of restitution, the elasticity of human tissues, and the dynamics of a seat rotating around a pivot at the base.
Head restraint geometry Described the relationship between the occupant's head and neck and the head restraint; usually in terms of backset and topset.
HIC Head injury criterion.
IARV Injury assessment reference values.
IIHS Insurance Institute for Highway Safety (www.iihs.org).
IIS Injury Impairment Scale.
Impact velocity The term impact velocity describes the velocity that one vehicle is traveling at the time it strikes another vehicle; in the context of injury mechanics, it is not very meaningful (see closing velocity).
ISS Injury Severity Scale.
Jerk The third derivative of position with respect to time. The change in acceleration with respect to time, expressed in fps3.
km/h Kilometers per hour; to convert km/h to mph multiply by 0.621.
kN kilo Newton (1,000 Newton).
Late whiplash Chronic whiplash. It is an unfortunate term because it can be misinterpreted to indicate a late onset of symptoms. However, it is widely used in the literature.
m/s Meters per second.
MADYMO Mathematical dynamic model; it is a multibody mathematical system used in crash testing simulation.
MAIS Maximum AIS.
Momentum Also known as linear momentum or vector momentum. Momentum is equal to the product of mass and velocity.
Msec Milliseconds (1,000 msec=1 second).
MTBI Mild traumatic brain injury, usually defined as a GCS of 13 or higher.
N Newton; 1 N=105 dyne or 0.225 lb.
NASS National automotive sampling system.
Near side impact A side impact in which the occupant is struck on the side nearest them (e.g., the driver is struck on the driver's door side).
NHTSA National Highway and Traffic Safety Administration, a branch of the Department of Transportation (www.nhtsa.gov).
NIC Neck injury criterion; a criterion of neck injury from MVC which considers the relative velocity and acceleration between the top of the neck and the bottom of the neck.
Nm Newton meter; 1 Nm=0.74 lbf ft.
Occupant/vehicle coupling The point at which the occupant and vehicle attain a common velocity.
PET Positron emission tomography.
PMHS Post mortem human subject (cadaver).
PMTO Post mortem test object (cadaver).
Pretensioner A (usually pyrotechnic) dynamic restraint tensioning system designed to draw an occupant into the seat.
Quasistatic loading Laboratory loading condition in which the load is applied gradually and increases incrementally so as to allow for the determination of failure loads.
Radian Or Rad; a unit of angular measurement equal to 57.3 degrees.
Recall bias A condition in which one group of subjects is more likely to recall events than another group (e.g., mothers of children born with cerebral palsy are more likely to accurately recall events during their pregnancies than mothers of healthy babies).
Re-entry The forward phase of whiplash.
Residual crush The amount of measurable crush resulting from a collision.
Retroflexion The opposite of anteflexion; +qy rotation (neck extension).
Ride down A term indicating a reduction in potential force due to an increase in the duration of acceleration time history (e.g., when the knee strikes the knee bolster, the acceleration of the knee is less due to the increased time it takes to compress the bolster padding).
Rotation A turning of the head, for example, from right to left around the z axis; qz.
SAE Society of Automotive Engineers (www.sae.org).
Safety cage The compartment of a vehicle in which occupants ride; also known as the occupant compartment.
SCL-90-R System checklist 90 revised.
sEMG Surface electromyogram.
Shear Also known as shear strain; a deformation of a solid body in which a plane in the body is displaced parallel to itself relative to parallel planes in the body; an example would be C5 moving anteriorly while C6 remains stationary.
SPECT Sometimes also SPET, single photon emission computed tomography.
SRS Supplemental restraint system (usually an airbag).
Subfailure A condition of ligaments or joints in which the normal architecture is preserved grossly but in which internal disruption of fibers has weakened the tissue to the point that dynamic loads are no longer tolerated; ligamentous instability.
SUV Sport utility vehicle.
Target vehicle The vehicle that is struck by another vehicle.
TBI Traumatic brain injury.
Tensile stress Stress directed along the longitudinal axis. Stretching in a linear fashion.
TMD Temporomandibular joint disorder.
Topset The distance from the top of the head to the top of the head restraint.
Torque The cross product of a vector from some reference point to the point of application of the force with the force itself. Also known as a moment of force. A twisting as in rotation of the head around the spinal axis.
Torso overspeed When the torso's speed is higher than that of the vehicle in rear impact crashes due, chiefly, to the inherent stiffness of the vehicle's seat back and its coefficient of restitution; once loaded during the rearward phase of the crash, it releases energy during the forward phase.
Unibody A shell type of construction in which the body and chassis are combined; also called monocoque.
WAD Whiplash-associated disorders, a term coined by the Quebec Task Force on WAD in 1995 to describe, in rather vague terms, all conditions attributable to whiplash.
Whiplash A term which is variously described in the literature as an injury to the cervical spine and/or supporting soft tissues resulting from motor vehicle trauma: the term, as most often used, excludes fractures or dislocations of vertebrae, and some authors (including myself) limit the term to rear impact crash vectors, while others consider it to include an injury from any type of crash scenario.
Witness marks Subtle residual signs of stress or strain to an object; seen for example as stretch marks on seat belt webbing.
Young's modulus The ratio of a simple tension stress applied to a material to the resulting strain parallel to the tension.