UNCONTROLLED FINAL POSITION
A final position reached by a traffic unit after an
accident without conscious human intervention.
UNCOUPLING LEVER OR ROD
A rod with a bent handle forming a lever, usually
attached to the end sill, by which the lock of the automatic coupler is opened
and the cars uncoupled without going between them. The lever proper is the part attached to the rod and operating
the unlocking mechanism, but in the case of freight cars, the lever and rod are
generally made in one piece.
UNDAMPED
Un-damped systems are those in which there are no
forces opposing the vibratory motion to dissipate energy.
UNDER DRIVE
Refers to a condition in which the vehicle's
transmission is in a gear having a ratio less than 1:1, that is, the engine
crankshaft turns at a faster rate than the vehicle's drive shaft. Opposite of overdrive. (Also see direct drive).
UNDER STEER
A characteristic of a motor vehicle that results in
a tendency to steer toward the outside of a curve. Motor vehicles with more weight on the front wheels than on the
rear or with too little pressure in the front tires are likely to understeer at
high speed.
UNDERBODY
Assembly of the floor pan and rear compartment pan
assemblies forming the lower closure of the body.
UNDERBODY DEBRIS
Debris consisting of mud, dust, rust, paint, snow,
or road tar loosened by collision from the underside of the vehicle body,
fenders, and other parts.
UNDERSTEER
A vehicle is understeer at a given trim if the
ratio of the steering wheel angle gradient to the overall steering ratio is
greater than the Ackerman steer angle gradient.
UNDERSTEER/OVERSTEER GRADIENT
The quantity obtained by subtracting the Ackerman
steer angle gradient from the ration of the steering wheel angle gradient to
the overall steering ratio.
UNIFORM ACCELERATION
Uniform acceleration is a constant acceleration,
meaning that the speed changes at a constant rate.
UNIFORM VEHICLE CODE
A specimen set of motor vehicle laws, designed and
advances as a comprehensive guide or standard for state motor vehicle and
traffic laws.
Units
Setup parameter to select the display units of measure in the ProDriver ( Detroit )
UNIVERSAL JOINT
A coupling providing transmission of power through
an angle.
UNREPORTED ACCIDENT
An accident which is not reported by police, but
may be reported to an insurance company, doctor, or to no one.
UNSPRUNG MASS
The un-sprung masses are the equivalent masses
which reproduce the inertia forces produced by the motions of the corresponding
un-sprung parts.
UNSPRUNG WEIGHT
The part of the weight of the motorcycle which is
not supported on springs (wheels and tires).
UPC
Uniform parts code, designed to classify auto parts
and used primarily for cost accounting.
UPPER BACK PANEL
Portion of body sheet metal between backlight and
decklid.
UPPER STRUCTURE
The portion of the body including the roof and
glass areas.
URBAN AREA
An area within boundaries fixed by State or Local
officials designated by the US Bureau of Census as having a population of 5,000
or more, and not within another urban area.