All countries have different laws for semi-trucks. The biggest difference between the EU, UK, and US is the length of the semi-truck. Most weigh about the same (US trucks weigh a little less than EU and UK trucks). Most are about the same width and height. In large countries truck s can be longer. They can have a larger cargo space. Longer semi-tractors drive better at faster speeds. Most US trucks are "convential" (bonneted in UK) with the engine under a hood in front of the cab. In the US shorter trucks weigh less. The weight has to be spread out over a long length. This is important on bridges. With long semi-trucks not as many trucks fit on the bridge and the weight of the axles are far apart. This length is important in the US.