page_title: Glossary of the American trucking industry
section_title: Vehicle parts
hierarchical_section_title: Glossary of the American trucking industry / Vehicle parts
caption_attribution_description: English: Interior of an Navistar International 9400i truck. The small blue illuminated square near the center of the photo is the Cummins Icon Idle system which allows the engine and the climate control to turn on only when it is needed as determined by a thermostat inside the truck. Switches on the dashboard (starting with the top left) include marker lamps, headlights, panel dimmer, windshield wipers, and fridge on/off; cruise set, cruise on/off, and powered mirror (passenger side only); engine brake power select (1, 2, or 3), engine brake on/off, diagnostics, and mirror heat. The large red octagonal knob is for the trailer brakes, and the yellow square one is for the tractor. Below the two knobs is the power divider switch, which engages both drive axles on the tractor (similar to a 4-wheel drive switch, although it is not recommended to operate interaxle differential switch at speeds over 35mph). At the bottom of the windshield, the large blue box which reads "E-ZPass" is an electronic toll collection transponder, for use on many of the toll roads on the East Coast of the United States. Other options (added by the driver) include, digital time, date, and exterior temperature. The paper taped to the dashboard is a list of the driver's favorite terrestrial radio stations from major cities across the continent.
context_page_description: A specialized set of jargon describe the tools, equipment, and employment sectors used in the trucking industry in the United States. Some terms may be used within other English-speaking countries, or within the freight industry in general. For example, shore power is a term borrowed from shipping terminology, in which electrical power is transferred from shore to ship, instead of the ship relying upon idling its engines. Drawing power from land lines is more efficient than engine idling and eliminates localized air pollution. Another borrowed term is "landing gear", which refers to the legs which support the front end of a semi-trailer when it is not connected to a semi-truck. Some nicknames are obvious wordplay, such as "portable parking lot", in reference to a truck that carries automobiles.
context_section_description: Baffle
  A partition or separator within a liquid tank, used to inhibit the flow of fluids within the tank. During acceleration, turning, and braking, a large liquid-filled tank may produce unexpected forces on the vehicle due to the inertia of liquids.
  Bulkhead
  A strong wall-like structure placed at the front of a flatbed trailer (or on the rear of the tractor) used to protect the driver against shifting cargo during a front-end collision. May also refer to any separator within a dry or liquid trailer (also called a baffle for liquid trailers) used to partition the load.
  Bunk
  See sleeper berth.
  Cab
  The interior of a truck where the driver sits to operate the vehicle.
  Cheater axle
  See lift axle.
  Dual wheels
  A pair of tire and wheel assemblies mounted side-by-side on a single axle hub. In some applications it is replaced by a super single. On pickup trucks it is sometimes called a dually. The assembly has a greater load carrying ability as compared to a single wheel. It also provides redundancy so if one of the two tires fail the second will maintain support preventing loss of vehicle control and allowing the vehicle to travel to a repair facility.
  Engine brake
  A braking system that utilizes the back pressure from the engine's pistons to slow down the vehicle. Commonly used to prevent heavy trucks from accelerating out of control while driving on steep downhill grades.
  Fifth wheel
  A pivoting platform on the rear of a truck tractor, used to support the front end of the trailer being towed that contains locking jaws that engage the trailer kingpin.
  Float
  A popular name for a wide tire used on the steer (front) axle (originally known as a Super Single).  Floats distribute the weight on the front axle over a wider area, preventing the tire sinking into softer ground.  Commonly used on dump trucks, cement mixers, etc.
  Glad hands
  Interlocking connectors attached to air hoses that supply air from the tractor to the trailer for air brakes.
  Headache rack
  See bulkhead.
  Jake brake
  A popular brand of engine brake. See also engine brake.
  Kingpin
  A large pin, underneath the front of a trailer, which interlocks with the fifth wheel.
  Landing gear
  A set of retractable, crank-up legs that support the front of a trailer when it is not connected to a tractor.
  Lift axle
  An air-powered axle that may be raised or lowered to the ground to provide greater load-carrying capacity, or to comply with axle weight requirements (see also Federal Gross Weight Bridge Formula).
  Retarder
  A device used to assist braking that does not use friction. such as engine braking or axle-mounted electromagnetic retarders. See also engine brake.
  Sleeper berth
  The portion of the truck's interior designated for sleeping, legally must contain a bed.
  Super single
  A popular name for a single, larger wheel and tire, (properly called a "wide-base tire"), substituted for a tandem assembly. The main benefit of a super single is a reduction in weight; combined with lower rolling resistance the super single promises better fuel economy. The disadvantage is the lack of tire redundancy from which tandem wheels benefit, as tire failure can disable the vehicle and increased highway wear, through the high point loading and scrubbing of road surfaces when making tight turns.
  Tandem axle
  A set of axles spaced close together, legally defined as more than 40 and less than 96 inches apart by the USDOT.
caption: The cab of an 18-wheeler
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