Wednesday, January 11, 2012



Truck, motor vehicle designed primarily for hauling cargo or for special work or service purposes. Trucks are usually larger and heavier than automobiles and differ in basic construction. Most modern automobiles have a unibody construction, in which the body itself provides structural support for the vehicle. Trucks, by comparison, are built around a strong metal frame, called a chassis, that supports the rest of the truck. Trucks usually have larger, more powerful engines and stronger suspensions than automobiles have. Large trucks have additional axles and wheels for carrying heavy loads.
Trucks come in many different varieties and are classified by weight, type, and the job they perform. Light trucks have a vehicle weight of up to 6,300 kg (14,000 lb) and are used for light hauling or towing, as well as for everyday transportation. Medium trucks have a weight of up to 15,000 kg (33,000 lb) and are typically used as dump trucks, garbage trucks, local freight-delivery trucks, and utility vehicles. Light and medium trucks are usually powered by gasoline internal-combustion engines, although some may be powered by diesel engines. Heavy trucks are over 15,000 kg (33,000 lb) in weight and are used primarily to pull trailers. Such trucks are often called semis (short for semitrailer), or tractor-trailer trucks, and use large diesel engines for power. Heavy trucks also include large vehicles designed for off-road work, such as large construction and mining trucks.
Trucks are also classified by their construction. Straight trucks have the body, or cab, and cargo compartment mounted on the same frame. All light trucks and most medium trucks are straight trucks. In a tractor-trailer truck, the engine and cab are part of the tractor unit. The trailer is a detachable unit, is separate from the tractor, and has its own suspension and wheels. It is joined to the tractor by a hinged platelike mounting device called a fifth wheel.
Light trucks include pickup trucks, minivans and full-size vans, and sport utility vehicles (SUVs). The engines, transmissions, and brakes of light trucks are usually similar to those used in passenger cars. Some light trucks offer four-wheel drive for off-road driving or driving on mud or snow. Light trucks are often used as passenger cars are for everyday driving, particularly in rural areas, but they also provide the ability to carry extra cargo when needed. They are used primarily for light hauling and construction work.
Most pickup trucks have a cab with two doors and a single bench seat that holds up to three passengers. Some have extended cabs with a rear seat or additional doors. The cargo area behind the cab is called the bed. It has raised sides and a fold-down tailgate at the back for loading and unloading cargo.
Vans are mechanically similar to pickup trucks, except that the cargo area is enclosed and is part of the body. Vans typically have side doors and a rear door in addition to the front doors. A cargo van is equipped with only a front seat, and the unfinished rear area is reserved for hauling items. Cargo vans are often used to deliver small parcels and goods in urban areas. A passenger van has multiple seats for carrying extra passengers, as well as side windows. Some have lengthened bodies to carry up to 15 or more passengers and are used like small buses. A conversion van is a cargo van that has been specially modified to carry passengers in luxury. Conversion vans typically have plush interiors, numerous accessories, and individual seats. Minivans are smaller vans intended primarily for hauling six to eight passengers. Minivans have mostly replaced station wagons as a family vehicle. Some minivans have rear-wheel drive, but most have front-wheel drive. They also have the same engines, transmissions, and suspension components as front-wheel-drive passenger cars. In addition to the two front doors, most minivans have one or two sliding side doors and a rear liftgate that opens vertically.
Many light trucks are adapted for special uses. Tow trucks have a derrick and winch for towing vehicles, or a tilting bed for carrying disabled vehicles. Many ambulances are also built on light-truck frames. Large police trucks, nicknamed paddy wagons, have an enclosed confinement area in the back for transporting groups of people who have been arrested. Some police departments in large cities also have specially armored trucks for use by riot teams or bomb disposal units.

Dump Truck
Dump trucks have large open beds for hauling loose material such as gravel or soil. To empty the bed's contents, a hydraulic lift inside the truck tilts the bed, dumping the contents behind the truck. Dump trucks are common at busy construction sites, where large amounts of building materials are frequently moved.

Medium-duty trucks have larger engines and frames than do light trucks and often have dual rear wheels or a second rear axle for carrying additional weight. Medium trucks are used primarily for local delivery work, for construction, and by municipal and utility fleets. Dump trucks have a hydraulically powered bed that tilts up and down for hauling and dumping rock, gravel, dirt, and debris. Garbage trucks have a large enclosed compartment and a hydraulic compressor for compacting and hauling refuse. Utility trucks with a boom and basket, nicknamed cherry pickers, are used by utility companies for lifting people up to work on utility lines or trees. Fire engines often have a large internal water tank and pump for fighting fires. Some carry large ladders for reaching the upper floors on multistory buildings. See Fire Fighting.
Tractor-trailer Truck
Tractor-trailer trucks, also called semis, haul much of the freight in the United States and a significant percentage of freight in the rest of the world. Trailers can deliver raw materials, refrigerated goods, and finished products to factories, warehouses, and markets. The tractor shown here includes a sleeping compartment so the driver can rest during long trips.

Heavy trucks have the largest frames and are usually powered by large diesel engines. They have multispeed transmissions, with as many as 18 gears, for pulling heavy loads. Most semis or tractor-trailer trucks have two rear drive axles, called dual tandems, each of which has dual tires on each side. Trucks with this arrangement are nicknamed 18-wheelers because of the total number of wheels under the truck and trailer.
When a heavy truck is assembled, the type of engine, transmission, brakes, axle arrangement, and other equipment used are usually specified by the individual or company that is ordering the truck. Almost all heavy trucks have power steering, cruise control, and air brakes. Air brakes use compressed air, rather than brake fluid, to activate and release the brakes. An air reservoir in the truck supplies air to the brakes through air hoses. The constant supply of air keeps the brakes released. Pressing on the brake pedal decreases the air pressure and applies the brake. If the brake system malfunctions or if the air hoses become punctured, the brakes apply themselves automatically as a safety precaution.
Most heavy trucks are designed for hauling goods over long distances, known as over-the-road hauling, although some are also used for local deliveries. The truck cab may be positioned behind the engine and hood or located directly over the engine. The latter is called a cab-over design, and it reduces the overall length of the truck-trailer combination. Cab-over trucks are hinged to tilt forward when engine access is necessary for maintenance or repairs. Most long-haul heavy trucks have a sleeper compartment, behind the cab, that contains a bed for the driver. The sleeper compartment is the truck driver’s home away from home and may be equipped with a television, a microwave oven, and a refrigerator. Most heavy trucks are also equipped with citizens band radio for communication. Some truck fleets use satellite tracking equipment to monitor their trucks, so the fleet operator or dispatcher can know a truck’s location at any time.
The large trailers pulled by semi tractors have their own rear suspension and wheels, with the front of the trailer being supported by the fifth wheel on the tractor. Semi trailers also have folding supports under the front that are lowered when the trailer is detached from the tractor and parked. The brakes on the trailer’s axles have air hoses that attach to the tractor’s brake system, so the tractor and trailer brakes work together. Trailers have their own signal, tail, and brake lights, all of which are powered by the tractor’s electrical system.
Trailers come in many different designs, depending on the intended cargo. Enclosed, or standard box-type trailers are used to haul a wide variety of goods and merchandise. Double trailers are often used on roads that have sharp turns. Double trailers resemble two smaller trailers linked together and can maneuver through tight turns more easily than standard trailers can. Size and weight restrictions apply and vary from state to state. In the United States, tractor and single trailer combinations generally must be less than 16 m (53 ft) in length and are limited to a maximum weight of 36,000 kg (80,000 lb). Separate weight limits apply to trailers with single or tandem axles and to double trailers. Maximum trailer height and width are dictated by state law and vary from state to state. For most states, the maximum height is 4.11 m (13.5 ft), and the maximum width is 2.6 m (8.5 ft). In some states, trailers may be equipped with additional wheels and axles to carry heavier loads.
A special type of enclosed trailer is an insulated and refrigerated “refer” unit, used for transporting perishable food items. Refrigerated trailers have a small engine mounted on the trailer for powering the refrigeration system. This allows the refrigeration unit to run continuously, even when the trailer is parked or disconnected from the tractor.
Piggyback trailers are enclosed trailers designed to be mounted on railroad flatcars for cross-country transport. Some have their own wheels and suspension, while others are sealed containers that are lifted off and placed on a trailer chassis. Sealed containers are also used on special ships, called container ships, to transport goods overseas.
Flatbed trailers are used to transport large objects such as construction equipment, industrial machinery, and oversized objects. Such trucks may be equipped with an Oversize Load warning sign and flashing lights, and may be accompanied by an escort vehicle to warn other motorists.
Platform trailers are essentially large containers with open tops for transporting produce and grain. Special trailers are also designed for hauling livestock, automobiles, and beverages.
Tank trailers, known as tankers, are used to haul chemicals, milk, gasoline, and other liquids. Tankers, as well as other trucks that carry flammable or toxic products, must display special warning emblems to warn police and firefighters in case of an accident.
Trucking has become the predominant means of delivering all types of goods, accounting for four-fifths of all domestic freight value in the United States. Trucks in the late 1990s hauled 1.5 trillion ton-kilometers of freight annually (a ton-kilometer is the movement of one metric ton over the distance of one kilometer). All types of manufacturing are also dependent on trucking for deliveries of parts and for shipping finished goods.
A trucking trade association estimates that about 9.7 million people in the United States are employed in trucking industry jobs, a figure that includes about 3.1 million professional truck drivers. In 2002 there were about 588,000 trucking companies in the United States. They generated over $580 billion in gross revenues.
At the beginning of the 21st century there were about 87.1 million trucks of all types on U.S. highways, out of a total of 217.6 million vehicles. The majority of trucks on the road were light trucks such as pickups and sport utility vehicles (SUVs); only about 21.3 million were trailers and semitrailers. In Canada, about 450,000 trucks are used to carry commercial freight.
Trucks that operate between states must be licensed in each state through which they travel, and their owners must pay road fees in each state. Trucks may be licensed to over-the-road commercial carriers, private delivery companies that operate their own trucks, or private owner-operators. Trailers are licensed separately from tractors and may be owned separately by a different company or fleet. There are about 4.7 million commercial semitrailers in the United States.
Drivers of over-the-road trucks must have a commercial driver’s license, which is obtained by special training and the passing of written and driving examinations. Drivers must also keep written logbooks of their hours and miles traveled, as these are regulated for safety purposes to minimize driver fatigue. Drivers who work for trucking companies are generally paid by the mile, while owner-operators and commercial carriers charge for freight by weight and distance. A typical commercial over-the-road truck is driven over 161,000 km (100,000 mi) a year.
Trucking operations are regulated by state and local agencies to ensure safety on the road. Trucks traveling on interstate highways and primary roads must be inspected at weigh stations to make sure they are not overloaded. Drivers are fined if the weight exceeds the limit allowed for each axle. Trucks are also subject to safety inspections and may be put out of service if the brakes, tires, or other safety equipment do not meet standards. Because big trucks are so large and heavy, they cannot stop or maneuver as quickly as cars and light trucks can. Of the almost 42,400 traffic fatalities that occurred in the United States in 2000, about 12 percent involved heavy trucks. In most car-truck accidents, the truck driver often is uninjured or suffers only minor injuries because of the size difference between the vehicles.
Various steam-powered carriages and vehicles were built in Europe from 1769 through the late 1800s. However, one of the first gasoline-powered vehicles for hauling cargo was built in 1896 by Gottlieb Daimler in Germany. The earliest trucks were essentially self-powered wagons, most of which had an open driver compartment in the front. In 1898 the Winton Company of Cleveland, Ohio, became one of the first manufacturers of trucks in the United States. In 1903 the first truck show in the United States was held in New York City. In 1911 the first transcontinental coast-to-coast trip by a truck was completed in 66 days.
In the early 1900s trucks were used primarily for local deliveries and limited intercity commerce. Roads were poor, and railroads controlled the long-distance shipping of freight. As roads improved and more highways were built, however, the role of trucking in commerce grew in importance. The Federal-Aid Road Act of 1916 promoted the building of paved roads between cities to facilitate travel and commerce. By the end of World War I (1914-1918), more than 600,000 trucks were in use in the United States. Trucks proved to be an invaluable method for moving both soldiers and supplies during the war, and were also used extensively as ambulances for transporting wounded soldiers.
In 1935 the Congress of the United States passed the Motor Carrier Act to expand the role of the Interstate Commerce Commission (ICC), a federal agency that regulated commerce between the states. The ICC was originally created to regulate commercial rail and water transportation. Its new authority allowed the ICC to establish regulations for trucking companies involved in interstate business.
As the nation’s highway system expanded, so did the use of trucking to move goods and produce. The construction of the interstate highway system in the late 1950s and 1960s made long-haul trucking not only practical but also highly competitive with rail freight. In 1980 the trucking industry was deregulated, allowing the establishment of many small independent trucking companies. Deregulation stimulated competition in the trucking industry and generally lowered the cost of shipping freight by truck.

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