Editing Semi-trailer truck (section)

==Role in trade ==
Modern day semi-trailer trucks often operate as a part of a domestic or international [[transport]] infrastructure to support [[Containerization|containerized]] [[cargo]] [[Shipping|shipment]].

Various types of rail [[Flatcar|flat bed train cars]] are modified to hold the cargo trailer or container with wheels or without. This is called ''[[Intermodal freight transport|Intermodal]]'' or ''[[Piggy-back (transportation)#Rail|piggyback]]''. The system allows the cargo to switch from highway to railway or vice versa with relative ease by using [[Crane (machine)#Gantry|gantry cranes]].

The large trailers pulled by a [[tractor unit]] come in many styles, lengths, and shapes. Some common types are: vans, reefers, flatbeds, [[sidelift]]s and tankers. These trailers may be refrigerated, heated, ventilated, or pressurized, depending on climate and cargo. Some trailers have movable wheel axles that can be adjusted by moving them on a track underneath the trailer body and securing them in place with large [[pin (device)|pins]]. The purpose of this is to help adjust weight distribution over the various axles, to comply with local laws.