What Are Semi Trucks?
The semi truck, also called a tractor-trailer rig or big rig, is a diesel-powered vehicle that pulls a large trailer. The 18-wheeled vehicle and trailer haul goods worldwide. In the United States, an estimated 2 million tractor-trailer rigs are on the road carrying goods for about a half-million companies. In 2006, big rig trucks traveled about 433 billion miles in the U.S.
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History
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Gasoline-powered trucks began to appear on North American roads in the 1890s. The truck's role in World War I demonstrated its versatility and vital nature in transporting material over long distances. An estimated 300 truck brands were on the road by the mid-1920s. By 1995, that number was reduced to only nine truck builders. Today, these makers produce about 150,000 trucks annually.
Semi Defined
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The semi truck and trailer consist of three axles. The front axle is located under the engine compartment of a standard cab vehicle to steer. The second axle behind the cab propels the vehicle. The third axle at the rear of the trailer features four sets of dual wheels to stabilize the trailer and carry the load.
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Classifications
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The big rig is either identified as a Class 7 or Class 8 truck. A Class 7 truck requires a commercial driver's license with a gross vehicle weight rating ranging from 26,001 lbs to 33,000 lbs. The Class 8 truck also requires a commercial driver's license and has a GVWR rating of more than 33,000 lbs.
Types
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The semi truck can pull tanker trailers that carry fuel or other liquids, refrigerated vans to carry produce and meats, dry freight vans for non-perishables, lowboys for ultra-heavy loads such as heavy equipment and multipurpose flat beds.
Size
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Common trailer sizes are 48 or 53 feet long, but can reach as long as 80 feet. Width is either 96 or 102 inches wide. The maximum height is 13 feet, 6 inches. Total maximum weight allowed on the highway is 80,000 pounds.
Design
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Truck builders redesign semi trucks about every five to seven years, similar to the timetable employed by automakers. Truck makers readily listen to customers' wants, needs and complaints and attempt to execute a design accordingly. Clay models and computer designs are used to determine aerodynamics and other features of the cab.
Future
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Fuel efficiency and emissions are the primary concern among truck builders today. More than 70 percent of the goods in the U.S. are transmitted by truck, far exceeding ships, aircraft and freight trains as the primary method of transportation. Since trucking is likely to remain the principal transportation, technological advancements will be made in aerodynamic and engine to reduce fuel consumption.
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References
Resources
- Photo Credit Old Shoe Woman/flickr.com; Scania Group/flickr.com; kenjonbro/flickr.com
