Semi-trailers are heavy-duty vehicles used for transporting goods across large distances. This type of truck is often preferred for transport over other types of trucks because it is easier to back up as it does not have a front axle and, hence, only one turning point. This offers flexibility in being able to be coupled and uncoupled fairly quickly. This means they can be shunted for loading. Additionally, if a power unit were to fail, then it is relatively easy to replace this unit without disturbing the cargo in any way. 

Semi-trailers can hold many different types of cargoes, ranging from edible goods to heavy machinery. As such, there are various different types of semi trucks to suit these cargo requirements:

Flat bed trailers 

These are one of the most common types of semi-trailers. Among flat bed trailers, there are additional configurations. Flat bed trailers may be operated manually or have a hydraulic system that allows the trailer to be tilted and the contents to be loaded or offloaded. The automatic ones are, of course, more expensive but offer convenience. These types of trailers are used for goods that can be stacked on top of each other and tied down. 

Box trailers 

These are also one of the common varieties of semi-trailers. Basically, they are a large metal box attached to the semi truck with doors at the back for access. These also come in custom designs where they may be refrigerated for the purpose of transporting meat and frozen foods as well as flowers. These types of trailers are typically used to transport goods of high value, including garments. These come in custom sizes depending upon the cargo requirements. 

Tanker trailers 

These are built for carrying liquids including gas and alcohol. These have to be strategically designed to balance the centre of gravity and safely carry the liquid goods. 

These heavy haulage vehicles can only be operated by qualified drivers who have undergone appropriate training to obtain their heavy haulage licence. Businesses may chose to rent or purchase their own semi-trailers. These vehicles are cheaper to operate then full trailers and are thus becoming increasingly popular in the transport industry. Additionally, they offer the advantage of having a longer cargo bed, allowing longer loads to be transported with ease. Multiple units can be combined to create a 'train', allowing more goods to be transported in a shorter span of time.