Drive five minutes on any U.S. road and you're bound to see an 18-wheeler truck. These vehicles are one of the mainstays of transportation in the USA and the men and women who drive these big trucks are American icons. But what, really, does a truck driver do?

A truck driver, obviously, operates an 18-wheeler, or semi. He may be an independent driver, owning his own rig, or she may work for a trucking company. The movie Smokey and the Bandit and the country/novelty song "Convoy" by C.W. McCall helped propel this profession into the public eye.

A truck driver must first be trained to drive an 18-wheeler. Driving this kind of vehicle is totally different from driving a car, a pickup truck, or even a small delivery truck. A semi has air brakes, numerous gears in the transmission and a thousand other differences from conventional vehicles. A truck driver must be trained in all the semi's systems and operations. She has to know what to do when going up or down a steep grade, so the brakes will not overheat. She has to know how to keep a load from shifting on a curve, which means she also has to know how to load the semi trailer properly.

The truck driving school teaches a novice how to park an 18-wheeler, how to maneuver in traffic and turn into narrow streets. A truck driver must learn different driving techniques, depending on where he is. One drives the rig one way in Los Angeles and another way on the flat Kansas Interstate.

When the truck breaks down, the truck driver must know some basic repair skills. She should know how to deal with the unique traits of a diesel engine and how to change a tire. She has to know how to connect and disconnect her tractor (the cab) from the trailer.

A truck driver is expected to drive long hours, keep track of them in the truck's logbook, get merchandise to its destination on time, load the truck, unload the truck, make sure the load in the truck matches the manifest sheet and a hundred other small duties. In short, the truck driver is responsible for his vehicle's operation, efficiency, management and safety, as well as for the load he carries. While some companies pay their drivers well, many truck drivers do not make a salary commensurate with what is expected of them. The hours are long and lonely. Burnout is common.

In the end, trucks and their human drivers are still the most common way to move consumer goods around the US, so if you're thankful for a well-stocked grocery store, buy a truck driver a cup of coffee to say thanks. He or she will appreciate it.