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Glossary of Truck Industry Terms R – U


Radar Detector.
Any device or mechanism to detect the emission of radio microwaves, laser beams or any other future speed measurement technology employed by enforcement personnel to measure the speed of commercial motor vehicles upon public roads and highways for enforcement purposes. Excluded from this definition are radar detection devices that met both of the following requirements:
(1) Transported outside the driver’s compartment of the commercial motor vehicle. For this purpose, the driver’s compartment of a passenger-carrying CMV shall include all space designed to accommodate both the driver and the passengers; and
(2) Completely inaccessible to, inoperable by, and imperceptible to the driver while operating the commercial motor vehicle.

Radial Tires.
The body ply cords run across the tire perpendicular to the tread.

A device of tubes and fins through which circulating water from the engine water jackets passes to give off excess heat and thus cool the engine.

Radiator Cap.
Located at the top of the radiator. It keeps the coolant from overflowing.

Radioactive Material.
Any material having a specific activity greater than 0.002 microcuries per gram (uCi/g), as defined in 49 CFR 173.403.

Radius Rods/Arm.
Suspension coupling designed to provide fore and aft location of an axle.

Slang term for open-top trailer using a tarpaulin cover.

Rail Vehicle.
A vehicle whose skeletal structure is fitted with stakes at the front and rear to contain logs loaded crosswise.

Rain Cap.
Protection device used on exhaust stacks to prevent rain entry when the engine is stopped.

The reflex or voluntary motion that occurs in response to a person perceiving an event.

Reaction Time.
The time that elapses between the point that a driver recognizes the need for action and the time that he takes the action.

Rear Axle Ratio.
Ratio of the speed of the propeller shaft to the speed of the axle shaft.

Rear Extremity.
The rearmost point on a motor vehicle that falls above a horizontal plane located 560 mm (22 inches) above the ground and below a horizontal plane located 1,900 mm (75 inches) above the ground when the motor vehicle is stopped on level ground; unloaded; its fuel tanks are full; the tires (and air suspension, if so equipped) are inflated in accordance with the manufacturer’s recommendations; and the motor vehicle’s cargo doors, tailgate, or other permanent structures are positioned as they normally are when the vehicle is in motion. Nonstructural protrusions such as taillamps, rubber bumpers, hinges and latches are excluded from the determination of the rearmost point.

Rear-View Mirrors.
Mirrors used to see on the sides and behind the vehicle. Should be at the proper angle and clean.

Reasonable Dispatch.
The performance of transportation on the dates, or during the period, agreed upon by you and the individual shipper and shown on the Order For Service/Bill of Lading. For example, if you deliberately withhold any shipment from delivery after an individual shipper offers to pay the binding estimate or 110 percent of a non-binding estimate, you have not transported the goods with reasonable dispatch. The term “reasonable dispatch” excludes transportation provided under your tariff provisions requiring guaranteed service dates. You will have the defenses of force majeure, i.e., superior or irresistible force, as construed by the courts.

Recap (Tires).
1) To recap a tire by bonding new tread rubber to the used tire; or
2) A tire that has been recapped.

Receiver/Consignee. The person or company to whom the goods are being shipped or consigned.

1) An exchange of rights, in motor transportation may involve granting equal rights to vehicles of several states in which reciprocity agreements are in effect; or
2) To give preference in buying to vendors who are customers of a buying company.

A change (made in transit) in the route, destination, or consignee as indicated in the original bill of lading.

Record of Duty Status (Driver’s log).
Daily record required to be completed by driver which shows driving, on-duty/not driving, sleeper-berth, and off-duty time.

Reefer Trailer.
A trailer designed for transporting food. Consists of insulated walls and self-powered refrigeration unit.

Slang for refrigerated trailer.

Reflective Material.
A material conforming to Federal Specification L-S-300, “Sheeting and Tape, Reflective; Non-exposed Lens, Adhesive Backing,” (September 7, 1965) meeting the performance standard in either Table 1 or Table1A of SAE Standard J594f, “Reflex Reflectors” (January, 1977).

Reflective Triangle.
Warning device carried on big rigs that is placed to warn other drivers when the rig is stopped. It is usually bright orange with red borders.

Reflex Reflector.
A device which is used on a vehicle to give an indication to an approaching driver by reflected lighted from the lamps on the approaching vehicle.

Refresher Training.
The training required periodically for qualified collectors, BATs, and STTs to review basic requirements and provide instruction concerning changes in technology (e.g. new testing methods that may be authorized) and amendments, interpretations, guidance, and issues concerning this part and DOT agency drug and alcohol testing regulations. Refresher training can be provided by any appropriate means (e.g. classroom instruction, Internet application, CD-ROM, video).

Refrigerated Trailer.
Used for hauling cargo that needs to be refrigerated. Also called a reefer.

Refuse to Submit (to an alcohol or controlled substances test).
A driver:
(1) Fail to appear for any test (except a pre-employment test) within a reasonable time, as determined by the employer, consistent with applicable DOT agency  regulations, after being directed to do so by the employer. This includes the failure of an employee (including an owner-operator) to appear for a test when called by a C/TPA (see 40.61(a) of this title);
(2) Fail to remain at the testing site until the testing process is complete. Provided, that an employee who leaves the testing site before the testing process commences (see 40.63(c) of this title) a pre-employment test is not deemed to have refused to test;
(3) Fail to provide a urine specimen for any drug test required by this part or DOT agency regulations. Provided, that an employee who doesn’t provide a urine specimen because he or she has left the testing site before the testing process commences (see 40.63(c) of this title) for a pre-employment test is not deemed to have refused to test;
(4) In the case of a directly observed or monitored collection in a drug test, fails to permit the observation or monitoring of the driver’s provision of a specimen (see 40.67(l) and 40.69(g) of this title);
(5) Fail to provide a sufficient amount of urine when directed, and it has been determined, through a required medical evaluation, that there was no adequate medical explanation for the failure (see 40.193(d)(2) of this title);
(6) Fail or declines to take a second test the employer or collector has directed the driver to take;
(7) Fail to undergo a medical examination or evaluation, as directed by the MRO as part of the verification process, or as directed by the DER under 40.193(d) of this title. In the case of a pre-employment drug test, the employee is deemed to have refused to test on this basis only if the pre-employment test is conducted following a contingent offer of employment;
(8) Fail to cooperate with any part of the testing process (e.g., refuse to empty pockets when so directed by the collector, behave in a confrontational way that disrupts the collection process); or
(9) Is reported by the MRO as having a verified adulterated or substituted test result.

Regional Director of Motor Carriers.
The Director of the Office of Motor Carriers, Federal Highway Administration, for a given geographical region of the United States.

Regular Route.
Refers to line-haul transport between given origins and destinations using assigned highways.

Regular Run.
The driver operates between the same points on each trip and may or may not have a regular starting and finishing time for each period of driving.

Relaxation Response.
A relaxation technique that calms the mind, body and spirit. The relaxation response helps combat the ill effects of stress.

Relay (Relay Driving).
A practice in which one driver takes a truck for 8 to 10 hours, then turns the truck over to another driver.

Relay Run.
Refers to a trip in which a driver drives for 10 hours and then goes off-duty as prescribed by the hours-of-service laws. Another driver takes the unit on to the next point. This cycle may be repeated several times as the truck is driven from origin to final destination by several different drivers.

Relay Emergency Valve.
A combination valve in an air brake system, which controls brake application and which also provides for automatic trailer brake application should the trailer become disconnected from the towing vehicle.

Relay Valve.
Valve designed to decrease the response time of the air brakes particularly on long vehicles. It is fitted near the local reservoir and brake chamber of the air brake system.

When dispatch sends a replacement tractor and driver to recover a load in transit.

Representative Vehicle.
A motor vehicle which represents the type of motor vehicle that a driver applicant operates or expects to operate.

Reservoir Air Pressure Gauge.
A gauge designed to measure the amount of air pressure in the air tanks in psi. If the air pressure drops below 60 psi, the vehicle is operating under unsafe conditions and a warning light or buzzer is activated.

Reservoir Tank.
See Dry Tank.

Goods sent to another destination under conditions which do not make the act subject to reconsignment rules and charges of the carrier.

Residential Delivery.
The bill of lading will specify the address and method of collecting payment if the shipment is to a residence.

Residential District.
The territory adjacent to and including a highway which is not a business district and for a  distance of 300 feet or more along the highway is primarily improved with residences.

A party against whom relief is sought or claim is made.

Restricted Articles.
Types of freight that cannot be handled at all or may only be handled under certain specific conditions.

Restricted Routes.
Routes that you are not allowed to go on because the route is hazardous or prone to accidents.

A device designed to assist the air brake system in slowing down the vehicle by dissipation the energy of motion by electrical or hydraulic means. See Jake Brake.

Retarder Systems.
Retarders supplement diesel truck service brakes and assist in reducing brake shoe overheating and resulting brake fade on long, steep downgrades.

Retention Groove.
A groove in the fifth wheel designed to retain lubrication for the ease of turning of the fifth wheel.

For the purposes of this part:
(1) Compliance review means an on-site examination of motor carrier operations, such as drivers’ hours of service, maintenance and inspection, driver qualification, commercial drivers license requirements, financial responsibility, accidents, hazardous materials, and other safety and transportation records to determine whether a motor carrier meets the safety fitness standard. A compliance review may be conducted in response to a request to change a safety rating, to investigate potential violations of safety regulations by motor carriers, or to investigate complaints or other evidence of safety violations. The compliance review may result in the initiation of an enforcement action.
(2) [Reserved]
(3) Safety management controls means the systems, policies programs, practices and procedures used by a motor carrier to ensure compliance with applicable safety and hazardous materials regulations which ensure the safe movement of products and passengers through the transportation system, and to reduce the risk of highway accidents and hazardous materials incidents resulting in fatalities, injuries and property damage.

Revolutions Per Minute (RPM).
The number of turns or rotations the engine makes in a minute. Engine RPM is expressed in hundreds on the tachometer.

Rib Tread.
Grooves in the tire tread that run parallel to the sidewalls. They are designed for highway speeds.

Slang for truck, tractor semi trailer, truck and full trailer, or other combination vehicle.

Rim Pull Torque.
A force at the tire to road contact point.

Part of the wheel that holds the tire in place. To prevent excess wear, loss of air pressure, or loss of a tire, rims should not be dented or damaged and should be rust free.

Rubber Manufacturers Association.

Rocky Mountain Double.
Larger than a standard double, but smaller than a turnpike double. The lead trailer is typically longer than the second trailer. overall length is 80 to 100 feet.

Rocky Mountain Double.
A vehicle composed of seven axles with a tractor, one 45-48 ft. trailer and one 26-28 ft. trailer.

Roll and Rest.
A single driver takes the truck from origin to destination.

Roll-up Door.
A style of rear door on a van trailer that is similar in operation to a garage door.

Rolling Parking Lot.
Slang for a car carrier.

Rolling Radius.
Distance measured from the center of tire/axle to the ground; the measurement is used for calculating gear speed.

Rolling Traction.
The friction occurring when one surface rolls over another.

The round disc of a disc brake assembly.

1) The course or direction that a shipment moves;
2) To designate the course or direction a shipment shall move; or
3) The carrier or carriers over which a shipment moves.

Routing Agency.
The State highway agency or other State agency designated by the Governor of that State, or an agency designated by an Indian tribe, to supervise, coordinate, and approve the MRHM routing designations for that State or Indian tribe.

Routing Designations.
Any regulation, limitation, restriction, curfew, time of travel restriction, lane restriction, routing ban, port of entry  designation, or route weight restriction, applicable to the highway transportation of NRHM over a specific highway route or portion of a route.

Routine Servicing.
Tasks that can be done by drivers, such as add fuel, oil, and coolant, or drain the moisture from the fuel and air systems.

RPM (Revolutions per Minute).
The measure of speed at which an object spins. It is most often used to describe engine crankshaft speed.

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.

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Saddle Tanks.
Barrel type fuel tanks that hang from the sides of the tractor’s frame.

A device, designed and constructed as to be readily demountable, used in driveaway-towaway operations to perform the functions of a conventional fifth wheel:
(1) Upper-half. Upper-half of a “saddle mount” means that part of the device which is securely attached to the towed vehicle and maintains a fixed position relative thereto, but doesn’t include the “kingpin;”
(2) Lower-half. Lower-half of a “saddle mount” means that part of the device which is securely attached to the towing vehicle and maintains a fixed position relative thereto but does not include the “kingpin;” and
(3) Kingpin. Kingpin means that device which is used to connect the “upper-half” to the “lower-half” in such manner as to permit relative movement in a horizontal plane between the towed and towing vehicles.

Saddle-Mount Combination.
Is a combination of vehicles in which a truck or tractor tows one or more trucks or truck tractors, each connected by a saddle to the frame or fifth wheel of the vehicle in front of it. The saddle is a mechanism that connects the front axle of the towed vehicle to the frame or fifth wheel of the vehicle in front and functions like a fifth wheel kingpin connection.

Society of Automotive Engineers.

Safe Haven.
An area approved in writing by local, state, or federal officials in which unattended vehicles carrying Class A or Class B explosives may be parked.

Safety Audit.
An examination of a motor carrier’s operations to provide educational and technical assistance on safety and the operational requirements of the FMCSRs and applicable HMRs and to gather critical safety data needed to make an assessment of the carrier’s safety performance and basic safety management controls. Safety audits do not result in safety ratings.

Safety Ratings.
(1) Satisfactory safety rating means that a motor carrier has in place and functioning adequate safety management controls to meet the safety fitness standard prescribed in 385.5. Safety management controls are adequate if they are appropriate for the size and type of operation of the particular motor carrier.
(2) Conditional safety rating means a motor carrier does not have adequate safety management controls in place to ensure compliance with the safety fitness standard that could result in occurrences listed in 385.5 (a) through (k).
(3) Unsatisfactory safety rating means a motor carrier doesn’t have adequate safety management controls in place to ensure compliance with the safety fitness standard which has resulted in occurrences listed in 385.5 (a) through (k).
(4) Unrated carrier means that a safety rating has not been assigned to the motor carrier by the FHWA.

Safety-Sensitive Function.
All time from the time a driver begins to work or is required to be in readiness to work until the time he/she is relieved from work and all responsibility for performing work. Safety-sensitive functions shall include:
(1) All time at an employer or shipper plant, terminal, facility, or other property, or on any public property, waiting to be dispatched unless the driver has been relieved from duty by the employer.
(2) All time inspecting equipment as required by 392.7 and 392.8 of this subchapter or otherwise inspecting, servicing, or conditioning any commercial motor vehicle at any time;
(3) All time spent at the driving controls of a commercial motor vehicle in operation;
(4) All time, other than driving time, in or upon any commercial motor vehicle except time spent resting in a sleeper berth (a berth conforming to the requirements of 393.76 of this subchapter);
(5) All time loading or unloading a vehicle, supervising, or assisting in the loading or unloading, attending a vehicle being loaded or unloaded, remaining in readiness to operate the vehicle, or in giving or receiving receipts for shipments loaded or unloaded; and
(6) All time repairing, obtaining assistance, or remaining in attendance upon a disabled vehicle.

Safety Valves.
Keep the air pressure from rising to a dangerous level.

Sand Piles.
Mounds or ridges built high enough to drag the undercarriage of the rig.

Looking far ahead, just ahead of the rig, and on both sides.

Search for and collect from discarded waste.

The surroundings, or environment, in which the driver operates. It includes the road conditions, weather, scenery, people, animals, and other road users.

Scheduled Preventive Maintenance.
Servicing that is based upon time or mileage since the last scheduled maintenance.

School Bus.
A CMV used to transport pre-primary, primary, or secondary school students from home to school, from school to home, or to and from school-sponsored events. School bus does not include a bus used as a common carrier.

School Bus Operation.
The use of a school bus to transport only school children and/or school personnel from home to school and from school to home.

Specialized Carriers and Rigging Association.

Screening Test (or Initial Test).
(1) In drug testing, a test to eliminate “negative” urine specimens from further analysis or to identify a specimen that requires additional testing for the presence of drugs.
(2) In alcohol testing, an analytical procedure to determine whether an employee may have a prohibited concentration of alcohol in a breath or saliva specimen.

Screening Test Technician (STT).
A person who instructs and assists employees in the alcohol testing process and operates an ASD.

Seat Belt.
Safety harness that holds you in the seat.

Seating Capacity.
Any plan view location capable of accommodating a person at least as large as a 5th percentile adult female, if the overall seat configuration and design and vehicle design is such that the position is likely to be used as a seating position while the vehicle is in motion, except for auxiliary seating accommodations such as temporary or folding jump seats. Any bench or split bench seat in a passenger car, truck or multi-purpose passenger vehicle with a gross vehicle weight rating less than 10,000 pounds, having greater than 50 inches of hip room (measured in accordance with SEA Standards J1100(a)) shall have not less than three designated seating positions, unless the seat design or vehicle design is such that the center position cannot be used for seating.

Secondary Braking System.
Can slow or even stop the rig if the service brake system fails.

Secondary Collision.
A collision that results from either being involved in an accident or taking evasive action to avoid an emergency.

Secondary Vehicle Controls.
Do not affect the rig’s power or movement but help the driver’s vision, communication, comfort and safety.

The Secretary of Transportation or the Secretary’s designee.

Security Seals.
Seals shippers place on cargo containers that do not let the driver fully inspect the load.

A term used loosely to refer to a tractor coupled with semi-trailer. Slang for tractor-trailer.

Semi-Automatic Transmission.
One that is essentially a manual transmission, but uses electronic controls to automate some of the gear changes.

Semi-elliptic Spring.
A leaf spring designed to operate with a pin-ended beam reacting with the loads as they are at mid-length bending. Modern designs utilize a shallow arc.

A trailer with only rear axles, supported and coupled to a tractor by the fifth wheel when in transit. Length can be up to 53 feet.

Any motor vehicle other than a “pole trailer” with or without motive power designed to be drawn by another motor vehicle and so constructed that some part of its weight rests upon the towing vehicle.

Serious Traffic Violation.
Conviction of any of the following offenses when operating a CMV, except weight, defect and parking violations:
(a) Excessive speeding, involving any single offense for any speed of 15 miles per hour or more above the posted speed limit;
(b) Reckless driving, as defined by sTate or local law or regulation, including but not limited to offenses of driving a CMV in willful or wanton disregard for the safety of persons or property;
(c) Improper or erratic traffic lane changes;
(d) Following the vehicle ahead too closely.
(e) A violation, arising in connection with a fatal accident, of State or local law relating to motor vehicle traffic control;
(f) Driving a CMV without obtaining a CDL;
(g) Driving a CMV without a CDL in the driver’s possession. Any individual who provides proof to the enforcement authority that issued the citation, by the date the individual must appear in court or pay any fine for such a violation, that the individual held a valid CDL on the date the citation was issued, shall not be guilty of this offense; or
(h) Driving a CMV without the proper class of CDL and/or endorsements for the specific vehicle group  being operated or for the passengers or type of cargo being transported.

Service Agent.
Any person or entity, other than an employee of the employer, who provides services specified under this part to employers and/or employees in connection with DOT drug and alcohol testing requirements. This includes, but is not limited to, collectors, BATs and STTs, laboratories, MROs, substance abuse professionals, and C/TPAs. To act as service agents, persons and organizations must meet the qualifications set forth in applicable sections of this part. Service agents are not employers for purposes of this part.

Service Brake System.
Is normally used to slow down or stop the vehicle.

Service Brakes.
Primary brakes used for normal brake application.

Set-back Axle.
Gear configuration where the front axle is set back from the front of the vehicle which creates a shorter turning radius and more of the vehicle’s weight is shifted to the front axle.

Seven Consecutive Days.
The period of 7 consecutive days beginning on any day at the time designated by the motor carrier for a 24-hour period.

Pivoting link between a leaf spring and its mounting.

Shift Lever.
Lever for manually changing gear in a manual transmission.

Shifting Chart.
Displays shifting lever position for all gears in a manual transmission shifting lever. Often found on the visor of the tractor.

The person or company who offers the goods for shipment.

Shipper’s Load and Count.
Indicates that the contents of a truck were loaded and counted by the shipper and not checked or verified by the carrier.

Shipping Container.
A container that is used for transporting and protecting urine specimen bottles and associated documents from the collection site to the laboratory.

Shipping Papers.
Papers used in connection with movement of freight.

Shipping Weight.
“Dry” weight of a truck including all standard equipment, but excluding fuel and coolant.

Happens whenever something reduces the flow of blood throughout the body and could kill a person. Keep the person warm and quiet.

Shock Absorbers.
Reduce the motion of the vehicle body as the wheels move over uneven surfaces.

Shoring Bar.
A device placed transversely between the walls of a vehicle and cargo to prevent cargo from tipping or shifting.

Short Ton.
2,000 pounds. Also called a net ton.

When quantity of freight received is actually less than that shown on the documents.

All logs typically up to 4.9 m (16 feet) long. Such logs are often described as cut-up logs, cut-to-length logs, bolts, or pulpwood. Shortwood may be loaded lengthwise or crosswise, though that loaded crosswise is usually no more than 2.6 m (102 inches) long.

Side Extremity.
The outermost point on a side of the motor vehicle that is above a horizontal plane located 560 mm (22 inches) above the ground, below a horizontal plane located 1,900 mm (75 inches) above the ground, and between a transverse vertical plane tangent to the rear extremity of the vehicle and a transverse vertical plane located 305 mm (12 inches) forward of that plane when the vehicle is unloaded; its fuel tanks are full; and the tires (and air suspension, if so equipped) are inflated in accordance with the manufacturer’s recommendations. Non-structural protrusions such as taillights, hinges and latches are excluded from the determination of the outermost point.

Side Marker Lamp (Intermediate).
A lamp shown to the side of a trailer to indicate the approximate middle of a trailer 30 feet or more in length.

Side Marker Lamps.
Lamps used on each side of a trailer to indicate its overall length.

Sided Vehicle.
A vehicle whose cargo compartment is enclosed on all four sides by walls of sufficient strength to contain articles of cargo, where the walls may include latched openings for loading and unloading, and includes vans, dump bodies, and a sided intermodal container carried by a vehicle.

Sight Distance.
The objects you can see at night with your headlights. Your sight distance is limited to the range of your headlights.

Sight Side.
The side of the tractor visible by driver, i.e., driver’s side. Opposite of blind side.

Signal or Identification Lights.
Truck lights on top, sides and back to identify it as a large vehicle. It is important for these lights to be clean, working, and the proper color.

Single Drive Axles.
Found on the rear of the tractor.

Single Drop Frames.
These are low beds that can haul heavy and oversized equipment without going over the height limits. Since these trailers are low to the ground they may have bottom clearance problems at railroad crossings, curbs, and large potholes, but not as much of a problem as a double drop frame.

Single-Employer Driver.
A driver who, in any period of 7 consecutive days, is employed or used as a driver solely by a single motor carrier. This term includes a driver who operates a commercial motor vehicle on an intermittent, casual, or occasional basis.

Single Reduction Drive Axle.
Drive axle in which the reduction in rotational speed between the drive shaft and the final drive is one stage.

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.

1) A wooden platform or pallet on which heavy articles or packaged goods are placed to permit handling; or
2) Failure of tires to grip the roadway because of loss of traction.

When the rig’s tires lose grip or traction of the road.

Slack Adjuster.
Lever designed to be an adjustable component fitted on the brake chamber push rod which is used to compensate for clearance between the brake shoe and drum when wear to the brake lining occurs. Some models are automatic while other are manually adjusted.

Slack Adjuster.
An adjustable device located on the brake chamber pushrod that is used to compensate for brake shoe wear.

Sleep Apnea.
A temporary suspension of breathing, occurring in some newborns (infant apnea) and some adults (sleep apnea) during sleep.

Commercial vehicle cab with a sleeping compartment for the driver.

Tractor cab equipped with bunk facilities so a driver may rest.

Sleeper Berth (SB).
A berth in the tractor cab in which the driver can sleep. Its size and other specifications are determined by the law.

Sleeper Berth Time.
Time spent resting in an approved type of sleeper berth.

Sleeper Operations.
The driver of a rig that has a sleeper berth can accumulate the required off-duty time in two periods as long as neither period is less than two hours.

Sliding assemblies for the fifth wheel and the tandem axle.

Sliding (Adjustable)Fifth Wheel (Slider).
Slides backward and forward. It can be locked into place to adapt to different loads. It greatly increases the flexibility of the total rig.

Sliding Fifth Wheel.
Fifth wheel assembly that allows it to be moved back and forth in order to adjust the distribution of the weight between the tractor and trailer axles.

Sliding Tandem (Slider).
Trailer tandems designed to be moved back and forth for the purpose of adjusting the distribution of weight between the axles and fifth wheel.

Sliding Traction.
The friction occurring when one surface slides across another.

Sliding trailer tandem axle assembly.
Is a tandem axle that allows the axle and suspension to slide, or move along, the frame rails of the trailer to make weight adjustments.

Slip Resistant Material.
Any material designed to minimize the accumulation of grease, ice, mud or other debris and afford protection from accidental slipping.

Slip Seat.
Operation where drivers change periodically, but the truck continues towards the same final destination.

Smoothbore Tank.
A tank that has no bulkheads or baffles.

Space Management.
Keeping a cushion of air around the rig at all times.

Spare Tire.
Additional tire used as a precaution in case something happens to the vehicle tires. Make sure they are properly secured, the right size, and inflated.

Special Purpose Vehicle.
(1) A trailer or semitrailer manufactured on or after January 26, 1998, having work-performing equipment that, while the motor vehicle is in transit, resides in or moves through the area tat could be occupied by the horizontal member of the rear impact guard, as defined by the guard width, height and rear surface requirements of 571.224 (paragraphs S51.1 through S51.3), in effect on the date of manufacture, or a subsequent edition.
(2) A motor vehicle, not described by paragraph (1) of this definition, having work-performing equipment that, while the motor vehicle is in transit, resides in or moves through the area that could be occupied by the horizontal member of the rear impact guard, as defined by the guard width, height and rear surface requirements of 393.86(b)(1).

Specimen Bottle.
The bottle that, after being sealed and labeled according to the procedures in this part, is used to hold the urine specimen during transportation to the laboratory.

The rate of motion of your rig.

Driving faster than the legal or posted speed limit or driving too fast for the conditions.

Indicates road speed in miles and kilometers per hour and is required by law to work.

Splash Guards (mud flaps).
Rubberized sheaths hanging behind the wheels that lessen the amount of water/mud kicked up in back of the trailer or truck. Make sure they are properly attached and not rubbing the wheels.

Split Shifting.
Coinciding gear shifts in the main and auxiliary transmissions.

Split Specimen.
In drug testing, a part of the urine specimen that is sent to a first laboratory and retained unopened, and which is transported to a second laboratory in the event that the employee requests that it be tested following a verified positive test of the primary specimen or a verified adulterated or substituted test result.

Mechanism that divides a gear into two or more ratios such as direct, overdrive, or underdrive. Controlled by a switch on the gearshift.

Splitter Valve.
Splits gears into direct or overdrive. This valve is controlled with a button on the top of the gear shift knob.

Spoke Wheel.
Made of two pieces. Difficult to balance and align the tires and rims. See Cast Spoke Wheel.

1) Someone who assists another driver in a backing maneuver;
2) A worker in terminal yard who parks vehicles brought in by regular drivers; or
3) A supervisor who checks the activities of drivers on the road.

Spread Axle (Spread Tandem).
A tandem axle arrangement spaced 54 inches apart or greater, substantially greater than the spacing of a conventional commercial vehicle, which is used to circumvent weight restrictions.

Spread Tandem.
A two-axle assembly in which the axles are separated by distances substantially greater than that in conventional assemblies.

Spring Brake.
Also known as dual chamber, piggy backs, MGM’s or maxi’s. Dual air chamber which incorporates an air supplied brake chamber and air compressed spring which actuates upon sudden air loss or activation of a dash mounted brake control switch. Brakes remain locked until the chamber is refilled with air or the spring is manually released.

Spring Capacity.
The amount of weight load that the spring in a suspension system is capable of carrying.

Spring Hanger.
A bracket on a truck chassis to which an eye of a leaf spring is attached.

Stab Braking.
First, apply the brakes fully. Then release the pedal partly when the wheels lock. Put on the brakes again when the wheels start to roll.

Device used to stabilize vehicle during turns. Also called a sway bar.

Stake Body.
Truck or trailer platform body with readily removable stakes which may be joined by chains, slats or panels.

Stamped Steel Top Plate.
One type of manufactured fifth wheel top plate. See Fifth Wheel Plate.

The practice of temporarily removing an employee form the performance of safety-sensitive functions based only on a report from a laboratory to the MRO of a confirmed positive test for a drug or drug metabolite, an adulterated test, or a substituted test, before the MRO has completed verification of the test result.

Standard Double.
Uses two semitrailers. The second trailer is converted into a full trailer by using a converter dolly.

Standard Double Rig.
A single axle tractor pulling a 28’ semitrailer and a 28’ trailer.

The amount of force required to begin movement. It is a function of engine torque, transmission ration, axle ratio and tire dimension.

A State of the United States, the District of Columbia, the Commonwealth of Puerto Rico, the Commonwealth of the Northern Mariana Islands, American Samoa, Guam and the Virgin Islands.

State of Domicile.
That State where a person has his/her true, fixed, and permanent home and principal residence and to which he/she has the intention of returning whenever he/she is absent.

Starter Motor.
An electric or air powered motor used to set the crankshaft in motion in order to start the engine.

Starting Routine.
Steps used to start the engine.

The routine followed for starting an engine.

State Primary Routes.
Within each state, these are the major routes.

Stationary Fifth Wheel.
A fifth wheel that is placed to get the best weight distribution between the tractor’s steer axle and the drive axle(s) of a properly loaded trailer, and is fixed in that position.

Steer Axles.
Front axles with steerable wheels.

Steering Arm.
Lever that moves the steering action from the tie rod to the steering knuckle.

Steering Arm.
The one on the right side attaches the tie rod to the wheels. The one on the left side is attached to the drag link.

Steering Axle.
Axle through which directional control of vehicle is applied. It may be powered or non-powered and there may be more than one steering axle on the unit.

Steering Gear.
Components by which a vehicle is steered.

Steering Gear Box.
Transfers the turning of the steering shaft to the Pitman arm.

Steering Shaft.
Connects the steering wheel to the steering gear box.

Steering System.
Allows you to steer the vehicle and should not have more than 10 degrees of steering wheel play.

Steering Wheel.
Connected to the steering shaft and controls the direction of the vehicle.

Steering Wheel Lash.
The rebound of motion of the steering wheel after it has been turned its maximum rotations.

Step Deck Trailer.
This type of trailer differs from the conventional flatbed in that the platform is typically lower than the height of the fifth wheel on the tractor.

Stop (Engine) and Emergency Stop.
Some tractors are equipped with a starter button and an “engine stop” switch. The engine stop is used to shut off the engine. Some tractors are equipped with an “emergency engine stop” switch to be used only when the engine starts to “run away” (exceeding the safe upper RPM limits). Once the emergency stop has been used, the engine will not start again until a mechanic has made repairs.

Stop Lamp Switch.
Activates the brake lights on the rear of the tractor and connected trailer when more than 5 psi of air goes to the brake chamber.

Stop Lamps.
Lamps shown to the rear of a motor vehicle to indicate that the service brake system is engaged.

Storage and Delay Charges.
An additional amount to be paid to the carrier if a delivery is postponed by the consignee or shipper or a shipper or a shipment must be stored before it can be delivered. These terms are stated in the bill of lading.

Straight Back Parking.
An alley dock backing technique in which the rig is pulled forward so that the rear is facing the target, then backed in.

Straight Bill of Lading.
A contract that provides for delivery of a shipment to the consignee. The driver does not need to get a copy from the consignee when the goods are delivered.

Straight Truck.
A single unit truck with the engine, cab, and cargo compartment all on the same frame.

Your body’s response to difficulty, frustration, fatigue, or anger.

Stud Piloted Wheel.
A type of disc wheel that is centered and is held onto the stud by the nuts.

Substance Abuse Professional (SAP).
A person who evaluates employees who have violated a DOT drug and alcohol regulation and makes recommendations concerning education, treatment, follow-up testing, and aftercare.

Substituted Specimen.
A urine specimen with creatinine and specific gravity values that are so diminished or so divergent that they are not consistent with normal human urine.

A type of blower, connected to the engine crankshaft, that forces air into the intake manifold at higher than atmospheric pressure to increase engine power and performance. See blower.

Supply Lines (Fuel).
The lines that carry a supply of fuel to each injector. Fuel enters the inlet connection and then the injectors.

Surface Transportation Board.
An agency within the Department of Transportation. The Surface Transportation Board regulates household goods carrier tariffs among other responsibilities.

Springs used to support a vehicle and its axles. Failure can result in tragic results.

Suspension System.
Supports, distributes, and carries the weight of the truck.

Sway Bar.
See stabilizer.

Swing Doors.
See Barn Doors.

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.

Sliding clutch mechanisms by which gear engagement is synchronized in a gearbox.

Systematic Seeing.
A driver’s visual search pattern that helps him or her know what to look at, what to look for, and where to look.

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A recording device in a tractor that automatically records the number of miles driven, the speed, the number of stops, and other pertinent statistics.

Displays the engine speed in revolutions per minute (RPM). It is a guide to knowing when to shift gears. The tachometer helps you use tee engine and transmission effectively during acceleration and deceleration.

Tag Axle.
Non-driven axle mounted behind the drive axle; the tag axle does not transmit power.

Tag Tandem.
The forward axle is live and the rear axle is dead. The dead axle tags along behind the live axle.

Tail Lamps.
Lamps used to designate the rear of a motor vehicle.

Tailgate Delivery.
The freight is unloaded and delivered at the tailgate (the back of the truck).

Following too close behind a vehicle.

Tandem Axle (Tandems).
Undercarriage arrangement where two or more axles are coupled closely together, normally between 40 and 72 inches.

Tandem Axle Tractor.
A tractor with two axles.

Tandem Axles.
Two axles that work together. There are three types of tandem axles.

Tank Trailer.
Any trailer on which tanks are mounted to contain fluid commodities in bulk, tanks may contain baffles to stop liquid from surging while in motion, pumps for loading/unloading may be self-contained.

Tank Vehicle.
Any commercial motor vehicle that is designed to transport any liquid or gaseous materials within a tank that is either permanently or temporarily attached to the vehicle or the chassis. Such vehicles include, but are not limited to, cargo tanks and portable tanks, as defined in part 171 of this title. However, this definition does not include portable tanks having a rated capacity under 1,000 gallons.

Tank Vehicles Endorsement.
An endorsement on a CDL that all drivers who transport liquids in bulk must obtain.

Tanker Trailer.
Trailer designed to carry liquids or dry bulk commodities.

Tare Weight.
Weight of a commercial vehicle exclusive of its contents including fuel, cargo, water and oil, subject to local definition.

An issuance (in whole or in part) containing rates, rules, regulations, classifications or other provisions related to a motor carrier’s transportation services. The Surface Transportation Board requires a tariff contain specific items under 1312.3(a) of this title. These specific items include an accurate description of the services offered to the public and the specific applicable rates (or the basis for calculating the specific applicable rates) and service terms. A tariff must be arranged in a way that allows for determination of the exact rate(s) and service terms applicable to any given shipment.

Tarp or Tarpaulin.
Is used to cover most freight and tied down with rope, webbing, or elastic hooks. To do its job properly, it should be tightly secured.

Temperature Gauge.
A device that indicates the temperature of such things as coolant, lubricating oil, and gear lube.

A building for the handling and temporary storage of freight as it is transferred between trucks. i.e., from a city pickup to a line haul truck.

Terminal Carrier.
The line haul motor carrier making delivery of a shipment at its destination. Terminal carrier means the last or final carrier.

A valve in the water jacket located at the point where the coolant leaves the engine. It opens to let the coolant go to the radiator for cooling after the engine temperature exceeds 180 degrees.

Controls the engine speed.

Through Bill of Lading.
A bill of lading used for shipments transported by more than one carrier that has a fixed rate for the service of all the carriers.

A combination of securing devices which forms an assembly that attaches articles of cargo to, or restrains  articles of cargo on, a vehicle or trailer, and is attached to anchor point(s).

Tie Rod.
Connects the front wheels together and adjusts their operating angle.

Chains, ropes and other implements used to secure cargo. Cargo should have at least one tie-down for each 10 feet of cargo.

Tie Rod Assembly.
The linkage that connects the left and right wheel steering arms.

Tire Chains.
Chain grids used on tires to provide additional traction on snowy, icy roadways. Tire chains are required during bad weather in some states.

Tire Pressure.
Amount of air pressure enabling tires to support their maximum weight. Check the manufacturer’s instructions for proper air pressure.

Tire Slides.
Occur when the forces from weight and acceleration of the rig are greater than the tires’ ability to maintain traction.

Tire Tread.
The part of the tire that makes contact with the road.

Provide traction and reduce road vibration, transferring braking and driving force to the road. During inspection, check tread depth, air pressure and general condition of the tires. Bald or worn tires can cause a blowout, hydroplaning, or make the vehicle hard to stop. Tires with low pressure make the rig hard to handle and cause unnecessary wear.

Truck Manufacturers Association.

The Maintenance Council.

A charge made for the use of a facility such as a bridge or turnpike.

Toll Roads.
Except for having to pay a toll, these roads are similar to the interstates.

A unit of measure. The movement of a ton of freight one mile.

Number of tons.

Twisting or turning force created by applying a torsional force.

Torque Curve.
A chart showing how the torque of an engine changes with its rpm.

Total Stopping Distance.
The driver reaction distance plus the vehicle braking distance.

Tow Bar Eye.
The ring at the end of a dolly that attaches a trailer to the pintle hook.

The contact between the tires and the road surface.

Truck designed to draw a semi-trailer with a fifth wheel coupler, referred to as a highway tractor to differentiate between farm tractor.

Pulls the trailer and drives the vehicle.

Tractor Parking Valve.
A round blue knob you can push in to release the tractor parking brake.

Tractor-Pole Trailer.
A combination vehicle that carries logs lengthwise so that they form the body of the vehicle. The logs are supported by a bunk located on the rear of the tractor, and another bunk on the skeletal trailer. The tractor bunk may rotate about a vertical axis, and the trailer may have a fixed, scoping, or cabled reach, or other mechanical freedom, to allow it to turn.

Tractor Protection System.
Secures the tractor’s air pressure if the trailer would break away from the tractor and snap the air lines.

Tractor Protection Valve.
Valve designed to make sure air is always available to tractor brakes. When activated (via dashboard control), it supplies air pressure to the supply system in the trailer.

Tractor Steering Axle.
Supports and steers the front end of the tractor.

Tractor Trailer.
Tractor and semi-trailer combination, an articulated vehicle.

The freight hauling part of the vehicle meant to be pulled by a tractor, a non-powered vehicle designed to be pulled by a tractor.

(a) Full trailer means any motor vehicle other than a pole trailer which is designed to be drawn by another motor vehicle and so constructed that no part of its weight, except for the towing device, rests upon the self-propelled towing motor vehicle. A semitrailer equipped with an auxiliary front axle (converter dolly) shall be considered a full trailer.
(b) Pole trailer means any motor vehicle which is designed to be drawn by another motor vehicle and attached to the towing motor vehicle by means of a “reach” or “pole,” or by being “boomed” or otherwise secured to the towing motor vehicle, for transporting long or irregularly shaped loads such as poles, pipes, or structural members, which generally are capable of sustaining themselves as beams between the supporting connections.
(c) Semitrailer means any motor vehicle, other than a pole trailer, which is designed to be drawn by another motor vehicle and is constructed so that some part of its weight rests upon the self propelled towing motor vehicle.

Trailer Air Reservoir.
The storage tanks on the trailer where pressurized air is held until needed to apply the trailer brakes.

Trailer Air Supply Valve (also called tractor protection valve).
In the open position, it provides air to the trailer brakes. In the closed position, it shuts off the air supply to the trailer.

Trailer Brake.
A hand-operated remote control that applies trailer brakes only. Located on the steering column or dash. Must never be used for parking also called hand valve, trolley brake, trolley valve handle, trailer hand brake, and independent trailer brake.

Trailer Brake Control Valve (also called hand valve, trolley valve, or independent trailer brake).
Operates the service brakes on the trailer only.

Trailer Emergency Relay Valve.
Used only in an emergency when the air supply is lost. If the air lines are crossed, the brakes will stay on.

Trailer Hand Valve Brake.
Valve in the cab used to operate the service brake of the trailer. To check it, apply the brake and begin to drive. If the unit moves, you have a problem and should stop immediately.

Popular piggyback arrangement which features conventional highway trailers placed on rail flatcars.

Transfer Pump.
A pump used to move fuel from fuel tank to injectors.

Is a case, or box, of gears located behind the clutch, it adjusts the power generated by the engine so it provides the right speed and torque for the job.

Transportation Charges.
Fees for transportation services.

Transportation of Construction Materials and Equipment.
The transportation of construction and pavement materials, construction equipment, and construction maintenance vehicles, by a driver to or from an active construction site (a construction site between mobilization of equipment and materials to the site to the final completion of the construction project) within a 50 air mile radius of the normal work reporting location of the driver. This paragraph does not apply to the transportation of material found by the Secretary to be hazardous under 49 U.S.C. 5103 in a quantity requiring placarding under regulations issued to carry out such section.

Treadle Valve (Foot Brake).
Controls the air that operates the brakes.

Three axle tractor or trailer where the three axles are located in close succession which distributes the weight.

Tri-Drive Axles.
Three axles in the same assembly. They are used where a load carrying advantage is needed.

Trip Leasing.
Leasing a company’s vehicle to another transportation provider for a single trip.

Trip Time Formula.
Trip Time = Distance divided by average speed.

A tractor plus semi-trailer plus two full trailers, typically having 7 axles with three 26-29 foot trailers.

Double-bottom unit, plus an additional trailer.

Triple-deck Livestock Trailer.
Trailer with three levels for transporting animals.

Triple Trailers.
Are combination rigs that have three semitrailers pulled by a tractor.

A combination consisting of a tractor, a semi trailer and two full trailers, coupled together.

Search out the source of a problem and attempt to solve it.

Vehicle designed for hauling cargo where the truck body is mounted to its chassis.

Any self-propelled commercial motor vehicle except a truck tractor, designed and/or used for the transportation of property.

1) Vehicle for hauling; or
2) Weight-bearing, wheeled device used to move goods from place to place.

Truck Load (TL) Carrier.
A 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.

Truck Tractor.
A vehicle used to pull one or more other vehicles, such as a semitrailer.

1) Quantity of freight that will fill a truck;
2) Quantity of freight weighing the maximum legal amount for a particular type of truck; or
3) When used in connection with freight rates, the quantity of freight necessary to qualify a shipment for a truckload rate, which is cheaper than a less-than-truckload rate.

A type of blower, powered by engine exhaust gases, that forces air into the intake manifold at higher than atmospheric pressure to increase engine power and performance. See blower.

Turn Around.
A type of trip or “run” in which the driver returns to the origin point immediately after his vehicle is unloaded and reloaded.

Turn Signal Lights.
Lights used to signal to other drivers that you are turning.

A driver travels for about five hours to a point destination and then returns to his or her home terminal. At the turn-around point, the driver might switch units or trailers for the return trip.

Turnpike Double.
A three-axle tractor pulling two tandem-axle semitrailers – nine axles in all. Turnpikes are most commonly used in the eastern states.

Twenty-Four Hour Period.
Any 24-consecutive-hour period beginning at the time designated by the motor carrier for the terminal from which the driver is normally dispatched.

The two drive axles of a tandem.

Twins (Twin Trailers).
See Doubles.

Two-Speed Axle.
A drive axle capable of being shifted through two gear ranges in order to double the number of gears available from the transmission.

Two Speed Rear Axle.
A rear axle having two selective gear ratios.

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Unclaimed Freight.
Freight which has not been called for by the consignee or owner, or freight that cannot be delivered.

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. See direct drive.

Unloader Valve.
A valve designed to control the air pressure in a commercial vehicle air brake system.

Upper Coupler Assembly.
A structure consisting of an upper coupler plate, kingpin and supporting framework which interfaces with and couples to a fifth wheel.

Upper Coupler Plate.
A plate structure through which the kingpin neck and collar extend. The bottom surface of the plate contacts the fifth wheel when coupled.

U.S. Coast Guard National Response Center.
Helps coordinate emergency forces in response to chemical hazards.

U.S. Numbered Routes. Major Through-Routes.
Those that parallel the interstates may be good alternatives in case of delays on the interstate.

Separating a tractor from a trailer.

Underpass and Bridge Clearance.
The minimum vertical clearance from the surface of the roadway to an overhead structure.

Under the Influence.
Refers to any driver operating under the influence of alcohol or drugs.

Uniform Straight Bill of Lading.
A contract that the parties cannot change. The goods must be delivered to the consignee or an authorized representative.

Universal Joints (U-Joints).
Allow the cab to move in any direction and let the drive shaft change its angel of operation.

Unladen Vehicle Weight.
See curb weight.

Unscheduled Maintenance and Repair.
Occurs when unexpected breakdowns or emergencies require immediate maintenance.

A steepening of the road, usually found around mountainous terrain or in the hill country; the opposite of a downgrade.

Allows the rig to gain speed. Moving up the gears provides more speed but less power.

Utility Service Vehicle.
Any commercial motor vehicle:
(1) Used in the furtherance of repairing, maintaining, or operating any structures or any other physical facilities necessary for the delivery of public utility services, including the furnishing of electric, gas, water, sanitary sewer, telephone, and television cable or community antenna service;
(2) While engaged in any activity necessarily related to the ultimate delivery of such public utility services to consumers, including travel or movement to, from, upon, or between activity sites (including occasional travel or movement outside the service area necessitated by any utility emergency as determined by the utility provider); and
(3) Except for any occasional emergency use, operated primarily within the service area of a utility’s subscribers or consumers, without regard to whether the vehicle is owned, leased, or rented by the utility.

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