In the United States, a commercial driver's license is required to drive any type of commercial vehicle weighing 26,001 lb (11,794 kg) or more. In 2006 the US trucking industry employed 1.8 million drivers of heavy trucks.
The United States' Interstate Highway System is full of bypasses and loops with the designation of a three-digit number.Usually beginning with an even digit, it is important to note that this pattern ishighlyinconsistent. For example, in Des Moines, Iowa the genuine bypass is the main route.Morespecifically, it is Interstate 35 and Interstate 80, with the loop into downtown Des Moines being Interstate 235. As itis illustratedin this example, they do not alwaysconsistentlybegin with an even number.However, the 'correct' designationis exemplifiedin Omaha, Nebraska.In Omaha, Interstate 480 traverses the downtown area, whichis bypassed byInterstate 80, Interstate 680, and Interstate 95. Interstate 95 then in turn goes through Philadelphia, Pennsylvania. Furthermore, Interstate 295 is the bypass around Philadelphia, which leads into New Jersey.Although this can all be rather confusing, it is most important to understand the Interstate Highway System and the role bypasses play.
The American Association of State Highway and Transportation Officials (AASHTO) is an influential association as an advocate for transportation. Setting important standards, they are responsible for publishing specifications, test protocols, and guidelines. All whichare usedin highway design and construction throughout the United States. Despite its name, the association represents more thansolelyhighways. Alongside highways, they focus on air, rail, water, and public transportation as well.
The Dwight D. Eisenhower National System of Interstate and Defense Highways is most commonly known as the Interstate Highway System, Interstate Freeway System, Interstate System, or simply the Interstate. It is a network of controlled-access highways that forms a part of the National Highway System of the United States. Named after President Dwight D. Eisenhower, who endorsed its formation, the idea was to have portable moving and storage. Construction was authorized by the Federal-Aid Highway Act of 1956. The original portion was completed 35 years later, although some urban routes were canceled and never built. The network has since been extended and, as of 2013, it had a total length of 47,856 miles (77,017 km), making it the world's second longest after China's. As of 2013, about one-quarter of all vehicle miles driven in the country use the Interstate system. In 2006, the cost of construction had been estimated at about $425 billion (equivalent to $511 billion in 2015).
The concept of a bypass is a simple one. It is a road or highway thatpurposelyavoids or "bypasses" a built-up area, town, or village.Bypasseswere createdwith the intent to let through traffic flow without having to get stuck in local traffic. In general theyare supposedto reduce congestion in a built-up area. By doing so, road safety willgreatlyimprove.
A bypass designated for trucks traveling a long distance, either commercial or otherwise,is calleda truck route.
Heavy trucks. A cement mixer is an example of Class 8 heavy trucks. Heavy trucks are the largest on-road trucks, Class 8. These include vocational applications such as heavy dump trucks, concrete pump trucks, and refuse hauling, as well as ubiquitous long-haul 6×4 and 4x2 tractor units. Road damage and wear increase very rapidly with the axle weight. The axle weight is the truck weight divided by the number of axles, but the actual axle weight depends on the position of the load over the axles. The number of steering axles and the suspension type also influence the amount of the road wear. In many countries with good roads, a six-axle truck may have a maximum weight over 50 tons (49 long tons; 55 short tons).