A semi truck accident is the most dangerous type of accident on the road, given the size and weight of semi trailers and the lack of control semi trucks have vs. passenger cars. No other type of vehicle is involved in more fatalities statistically than a semi truck, and with roughly 15.5 million semi trucks operating on the road, the risk of this type of accident is serious. Semi tuck accidents happen for a large number of reasons, most of which are not the fault of semi drivers, the majority of who are professionals and licensed to drive such big rigs. Mechanical failures, brake failure, tire blowouts, unlicensed semi drivers, unbalanced or overweight loads and driver fatigue are common causes of these crashes.