Truck driver fatigue is a major cause of trucking accidents. While there are federal regulations in place that limit the number of hours a truck driver can drive at a time, these laws are often circumvented by drivers who only get paid when they are behind the wheel. In most all cases, the trucking companies are aware their drivers are exceeding the number of allowable hours, and simply look the other way, since their financial bottom line is also dependent on the truck remaining on the highway. There are some that believe as many as 40-50 percent of semi-truck accidents are caused by driver fatigue.