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- R -
Relay (Relay Driving)
Common practice in the less-than-truckload
industry, in which one driver takes a truck for 8
to 10 hours, then turns the truck over to another
driver, pony express style.
Reefer
Refrigerated trailer with insulated walls and a
self-powered refrigeration unit. Most commonly
used for transporting food.
Retarder
Device used to assist brakes in slowing the
vehicle. The most common type of retarder on
over-the-road trucks manipulates the engine's
valves to create engine drag. (This type is
commonly referred to as "Jake Brake" because the
predominant manufacturer is Jacobs Vehicle
Equipment Co.) Other types of retarders include
exhaust retarders, transmission-mounted hydraulic
retarders and axle-mounted electromagnetic
retarders.
RFG (Reformulated Gasoline)
Gasoline blended with pollution reducing
additives.
RoadRailer
Semitrailer specially designed to travel both on
highway and on rails. Manufactured by Wabash Corp.
Rolling Radius
Tire dimension from center of the axle to the
ground; measured with tire loaded to rated
capacity. Used in calculating geared speed.
RPM (Revolutions Per Minute)
Measure of the speed at which a shaft spins. Most
often used to describe engine crankshaft speed.
Indicated by a tachometer.
Runaway Truck Ramp
Emergency area adjacent to a steep downgrade that
a heavy truck can steer into after losing braking
power. Usually two or three lanes wide and several
hundred feet long, the ramp is a soft,
gravel-filled pathway which absorbs the truck's
forward momentum, bringing it to a safe stop.
Depending on the surrounding terrain, the ramp may
be level or run up or down hill.
- S -
Semitrailer
Truck trailer supported at the rear by its own
wheels and at the front by a fifth wheel mounted
to a tractor or dolly.
Setback Axle
Front steering axle moved rearward from the
generally accepted standard position. Advantages:
Shorter turning radius and more of a vehicle's
weight shifted to front axle.
Shipping Weight
"Dry" weight of a truck including all standard
equipment, but excluding fuel and coolant.
Single-Source Leasing
Service in which companies can lease drivers and
trucks from the same source, rather than having to
procure them from different companies.
Sleeper
Sleeping compartment mounted behind a truck cab,
sometimes attached to the cab or even designed to
be an integral part of it.
Sleeper Team
See
Team.
Sliding Fifth Wheel
Fifth wheel mounted to a mechanism that allows it
to be moved back and forth for the purpose of
adjusting the distribution of weight on the
tractor's axles. Also provides the capability to
vary vehicle combination lengths.
Sliding Tandem (Slider)
Mechanism that allows a tandem axle suspension to
be moved back and forth at the rear of a
semitrailer, for the purpose of adjusting the
distribution of weight between the axles and fifth
wheel.
Speedability
Top speed a vehicle can attain as determined by
engine power, engine governed speed, gross weight,
driveline efficiency, air resistance, grade and
load.
Spoke Wheel
See
Cast Spoke Wheel.
Spread Axle (Spread Tandem)
Tandem axle assembly spaced further apart than
the standard spacing of 54 inches. The
U.S. federal bridge formula favors trailer axles
with an eight or nine foot spread by allowing
higher weight than on tandems with standard
spacing.
Straight Truck
See
Truck.
SUV
Sport/utility vehicle.
Synchronized Transmission
Transmission with built-in mechanisms to
automatically "equalize" the speed of its gears to
allow smooth shifting without the need to
double-clutch.
- T -
Tag Axle
See
Axle.
Tare Weight
See
Chassis Weight.
Tandem Axle (Tandems)
Pair of axles and associated suspension usually
located close together. (see
Spread Axle)
Team (Driver Team)
Team of two drivers who alternative driving and
resting.
TEU (Twenty-Foot Equivalent Unit)
Standardized unit for measuring container
capacity on ships, railcars, etc.
TL (Truckload)
The quantity of freight required to fill a
trailer; usually more than 10,000 pounds. (see
LTL)
TL Carrier
Trucking company which dedicates trailers to a
single shipper's cargo, as opposed to an LTL (Less
Than Truckload) carrier which transports the
consolidated cargo of several shippers and makes
multiple deliveries. (see
LTL Carrier)
TOFC (Trailer On Flatcar)
Method of moving cargo which involves
transporting semitrailers on railroad flat cars.
(see
Piggyback)
Tractor
Truck designed primarily to pull a semitrailer by
means of a fifth wheel mounted over the rear
axle(s). Sometimes called a truck tractor or
highway tractor to differentiate from it from a
farm tractor.
Tractor Trailer
Tractor and semitrailer combination.
Tri-Axle
Truck, tractor or trailer with three axles
grouped together at the rear. (see
Tridem)
Tridem
Group of three axles on a truck, tractor or
trailer. Tridems are most common on European
semitrailers.
Trip Leasing
Leasing a company's vehicle to another
transportation provider for a single trip.
Trip Recorder (On-Board Computer)
Cab-mounted device which electronically or
mechanically records data such as truck speed,
engine rpm, idle time and other information useful
to trucking management.
Truck
Vehicle which carries cargo in a body mounted to
its chassis, rather than on a trailer towed by the
vehicle.
Twins (Twin Trailers)
See
Doubles.
- U -
ULEV
Ultra-low emissions vehicle.
Upper Coupler
Load bearing surface on the underside of the
front of a semitrailer. It rests on the fifth
wheel of a tractor or dolly and has a
downward-protruding kingpin which is captured by
the locking jaws of the fifth wheel.
- V -
VIN (Vehicle Identification Number)
Assigned by the manufacturer, this number is
unique to each vehicle and appears on the
vehicle's registration and title.
VMRS (Vehicle Maintenance Reporting Standards)
Set of codes developed to facilitate computerized
tracking of parts and labor used in equipment
repair. Established and maintained by the American
Trucking Associations.
- W -
Walking Beam Suspension
Type of truck and tractor rear suspension
consisting of two beams, one at each side of the
chassis, which pivot in the center and connect at
the front to one axle of a tandem and at the rear
to the other axle.
WIM (Weigh-In-Motion)
Technology for determining a vehicle's weight
without requiring it to come to a complete stop.
- Y -
Yard Jockey
Person who operates a yard tractor.
Yard Tractor (Yard Mule)
Special tractor used to move trailers around a
terminal, warehouse, distribution center, etc.
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