Tractor Trailer Trucks-Types of Tractor Trailers
A tractor trailer truck is a truck with a tractor (in the front, with the engine or motor) and a trailer (to move goods) behind it. There are many different configurations and sizes for this type of vehicle. A tractor trailer truck may also be referred to as an articulated truck, which comes from the British version (articulated lorry); it means the same thing.
Special operator permits (driver’s licenses) are required for someone to operate a tractor trailer truck.
A tandem trailer consists of the towing vehicle with two trailers behind it.
A semi-trailer truck (semi) supports the trailer by the towing vehicle, and the trailer has wheels only at the rear end but no front axle. The front of the trailer may also be supported by an assembly that attaches and detaches to the trailer, called a dolly. When the trailer is detached from the tractor portion, the front of it is supported by legs that are lowered.
The tractor is attached to the trailer by a ‘fifth wheel’ (a disk with a V shaped slot and a locking mechanism, mounted on the rear end of the tractor) and a ‘kingpin’ (a cylindrical pin, mounted on the front end of the trailer).
All semi trailer trucks are constructed with the same components: the detachable semi trailer, the engine compartment on the tractor, the cabin (sometimes with a sleeper portion), an air dam, fuel tanks, fifth wheel coupling, the cargo space (enclosed), and the landing gear to support the trailer when it is not attached to the tractor.
Semi-trailer trucks, which carry freight, can be found in several configurations and varieties. There is the dry freight van, the refrigerated van (reefer), the flatbed trailer (standard, step-deck, double drop, lowboy, etc.), and tank, or tanker trucks.
Because trailer trucks are very large and are capable of carrying great weight, there are limits for weight and size. If a shipment is oversized it may require a special permit, and be required to follow other regulations, such as speed. If the trailer truck is going to be driven in an area that permits weight loads lighter than what it is carrying, a special permit may be required. Road weight limits vary to prevent road damage. Regulations for size and weight vary from state to state, but most trucks are built to Department of Transportation (DOT) standards, which covers the interstate system, which is used m by the majority of trailer trucks.
Semi trailer trucks usually have 3 axles (2 on the tractor, and 1 on the trailer), and can have from 10 to 18 tires, or more. The front axle on the tractor is used for steering, with 2 tires. The rear axles, for driving the load, have double sets of wheels on each side.
A sleeper cab truck (truck outfitted with sleeping arrangements for the operator) has another configuration of axle and wheels. The sleeper part of the tractor can be anything from a small bunk type bed to a fancy miniature apartment, complete with arrangements for some cooking.
Trailer trucks are also starting to be manufactured with a ‘skirted’ trailer, so that the area of the road and the trailer bottom (previously open) becomes more blocked, to reduce air drag and for better fuel economy. Aerodynamic panels may also be found on the top of the tractor, to reduce air drag.
A two axle trailer may also be seen towing two 1 axle trailers (doubles). Some states further allow ‘longer combination vehicles’ (LCVs); these can include triples, ‘turnpike doubles’, and ‘rocky mountain doubles’, each having different size and weight specifications and allowances. LCV regulations vary from state to state.
The box truck (a/k/a cube truck, cube van, box van or straight truck) is a truck with a cube shaped cargo area; it is smaller than a trailer truck. The rear door of the cargo compartment can roll up. Sometimes the cargo area can be accessed through the cab area. They carry smaller cargos, such as appliances. Moving vans are examples of box trucks. While the cargo areas are smaller, the cab areas are often the same size as is found on large trailer trucks.
The refrigerator truck (reefer) is specifically designed for hauling perishable freight, such as frozen items, dairy items, etc. They are manufactured with cooling systems for mechanical refrigeration, regulating the required temperature for the cargo. They can be ice cooled or cooled with dry ice (carbon dioxide). Fuel cell auxiliary power units are being tested, to provide additional power.
A tanker truck carries liquid loads, gases, gasoline and other fuels, milk, water, concrete, chemicals, or dry bulk cargo. The large ones are similar to a railroad tank car in appearance. For liquid loads, there are baffles and sometimes compartments in the trailer compartment to prevent extreme load shifting when accelerating or decelerating. The can be insulated and pressurized if desired. It is difficult to drive them because they have a high center of gravity. Their shape is cylindrical. Depending on the contents, they are constructed of various materials.
Smaller versions are used as septic tank service trucks for hauling the sewage away; they are equipped with pumping systems. They deliver liquid petroleum gas to homes, and transport fuel at airports.
The flatbed truck has a bed body with mo sides or roof. Cargo is loaded quickly and easily. Heavy loads such as logs, construction equipment or loads requiring more space than is available in a standard walled trailer are hauled on flatbed trucks.
A car hauler (car carrier) is a trailer truck with an open back and slots, or levels for compartmentalizing vehicles for transporting multiple vehicles at one time. The vehicles fit into specialized areas designed for fitting tires and they are strapped down for securing them with chains and heavy ties. The car carrier usually has an open trailer, but they are also made with closed trailers, usually for moving antique or very expensive vehicles.
The lowboy trailer is a semi-trailer with two different deck heights on the trailer. One height is found immediately after the ‘gooseneck’ connection to the tractor, and the other begins before the wheels. The cargo decks on these open trailers are very low to the road surface.
They can have a fixed gooseneck (lighter loads), a mechanical gooseneck (for a longer deck length), a hydraulic connection, or other configurations. They are often used for moving construction equipment, such as bulldozers.
Trailer trucks have a variety of transmissions. For maximum operator control a manual transmission is used; a semi-automatic transmission, or an automatic transmission. Gear ratios can go as high as eighteen or even more; these gear ratios operate in conjunction with the braking and accelerating power of the trailer for better control during curve negotiations and up or down hill hauling. The clutch in a trailer truck is also specially designed.
The lights on a trailer truck are connected from the tractor to the trailer via cables. They control the brake lights, turn signals, running lights, and any other lights on a truck. The cables are sometimes referred to as the pigtail because they are shaped like springs or coils; they are more flexible this way and the coil shape presents less tension so they break less. There are various minimum requirements for the number of lights a trailer truck or semi trailer must have.
Certain mirror configurations are also found on trailer trucks. Additionally, they are equipped with mud flaps, or underride guards, to provide protection to other vehicles and people, if debris is thrown off of the tires of the truck, or if a vehicle runs into the back of the truck.
The semi-trailer truck is more flexible for road use than the full trailer truck. The trailer can be taken off and put on quickly, if the tractor breaks down another one can easily be substituted with minimal delay in delivering the load, they are easier to drive in reverse, they have a smaller turning radius, etc.
However, a semi-trailer, resting on the top of the tractor portion, has a higher center of gravity so it is more likely to topple over. It is also more difficult to drive in snow or on mud, thereby being more likely to jackknife.
There are other, less common types of trailer trucks than the ones mentioned above, but they are not well known or used in a lot of industries or manufacturing settings.
If it was not for the request of a man with a pleasure boat, the semi trailer truck would not have been designed in 1914 in the Detroit area. A gentleman asked a blacksmith/carriage builder to construct a trailer for carrying his boat and was so pleased with the result that he commissioned additional trailers for his business, to haul lumber and wood products. The blacksmith, August Charles Fruehauf, began building semi-trailer trucks, incorporating his business in 1918.
The underride guard portion of trailers was used starting after the 1967 accident in which actress Jayne Mansfield was killed, when her vehicle hit the back of a tractor trailer truck. It provides more protection for vehicle passengers than merely the windshield of the car or the car’s dashboard area.
The trailer truck has become very popular in the media, and has been the ‘star’ (or co-star) of several television shows and in the movies (BJ and the Bear, Knight Rider Trick MY Truck, Smokey and the Bandit, Duel, Convoy, Ice Road Truckers), appeared in cartoons (The Transformers). Trailer trucks have also been noted in music (“Convoy”, country music genre, the band BigRig is named after trucks), and in video games and video racing games.