Types of Semi Trucks
Semi-trucks consists of a power unit, or tractor, and a trailer. These trucks are also known as 18-wheelers for the number of tires on the combined unit. For a specific trucking purpose, the type of tractor and trailer will be matched for cost efficient transport of the cargo. Semi-trucks fall into several broad categories.
Over-the-Road Long Haul
Over-the-road semi-trucks haul goods from city to city across the country. The tractor will be an aerodynamic unit with a sleeper cab. The trailers for over-the-road trucks will be aluminum dry vans for packaged goods, refrigerated vans for fresh or frozen food, tankers for fuel, water, chemicals and milk and flatbed trailers for bulky items or building products. Over-the-road trucks have a maximum weight of 80,000 pounds and they are designed to maximize the load capacity and fuel efficiency.
Local haul semi-trucks work a smaller local market, moving a wide range of products. The tractors do not have sleeper cabs and have wheelbases and axles set up for maneuverability. Some will use the same types of trailers as long haul trucks, but end-dump and bottom-dump trailers and flatbeds with cranes are common local use trailers. State laws vary concerning truck weights and applications, so local haul trucks will be built specifically for the local market. A local haul bottom dump truck in California is completely different than the truck used for the same purpose in Nevada.
Heavy haul semi-trucks are set up to move extremely heavy pieces of construction equipment or manufactured equipment. These trucks will significantly exceed the 80,000-pound limit of regular highway trucks. Heavy haul tractors have the most powerful diesel engines available and 18-speed transmissions. Also, the axle capacities will be higher, 20,000-pound front axles and 46,000-pound rear tandems compared to 12,000 pounds and 34,000 pounds for highway tractors. Heavy haul semi-trucks also use special trailers than can split in the middle to allow the loading of heavy equipment and have low decks to carry tall pieces of equipment. Low boy trailers also have many more tires than the eight on regular highway trailers. Both the tractor and trailer of a heavy haul semi-truck are much more expensive than those used for long or local haul trucking.
The tractors and trailers of long haul, local haul and even heavy haul can be used for other purposes if the need arises. Some semi-trucks, however, can only be used for a single purpose. A common example is the car hauler. A car hauler has the tractor cab modified to work with a specific car trailer. Another specialty truck hauls concrete powder from the manufacturing facility to the ready-mix plant. The tractor has a special pump system that moves the concrete powder in and out of the trailer efficiently.