A semi-trailer truck (more commonly semi truck or simply “semi”) is the combination of a tractor unit and one or more semi-trailers to carry freight.

A semi-trailer attaches to the tractor with a fifth-wheel coupling (hitch), with much of its weight borne by the tractor. The result is that both the tractor and semi-trailer will have a distinctly different design than a rigid truck and trailer.

Odisha Woman Driving Trailer Truck Carefully – VIDEO

It is variously known as a transport in Canada; semi or single in Australia and New Zealand; semi, tractor-trailer, big rig, or eighteen-wheeler in the United States; and articulated lorry, abbreviated artic, in the United Kingdom, Ireland and New Zealand.

These vehicles have been criticised on safety grounds, including when a study in London found that they caused a disproportionate number of annual cyclist casualties.

A “trailer” supports its own weight. An example would be a Conestoga wagon, or a farmer’s hay wagon. They have wheels at both front and back; the tractor PULLS the load, but doesn’t CARRY the load.

You typical “car/pickup” trailer is largely the same, carrying 85–90% of its own weight.

A SEMI trailer has wheels at the back of the trailer ONLY. That means the tractor has to both pull the load, and bear a significant portion of the weight of the load. Which is why a pickup cannot pull a semi trailer, even the “big, bad” one-tons that might actually be rated to TOW a lightly-loaded semi trailer: they can tow it, but they can’t carry it!