How long have 18 wheelers existed?

18-wheelers, also known as semi-trucks or tractor-trailers, began to emerge in the early 20th century, with significant development occurring in the 1930s. The combination of a truck tractor and a detachable trailer allowed for more efficient transportation of goods. By the 1950s, the design and usage of 18-wheelers became more standardized, leading to their widespread adoption in the freight industry. Today, they are a crucial component of logistics and transportation networks worldwide.