Pre-1986
Driving commercial motor vehicles (CMVs), which are primarily tractor-trailers (or Longer Combination Vehicles (LCVs)), requires advanced skills and knowledge above and beyond those required to drive a car or other light weight vehicle. Before implementation of the Commercial Driver's License (CDL) Program in 1986, licensing requirements for driving larger vehicles and buses varied from state to state.
Many drivers were operating motor vehicles that they may not have been trained or qualified to drive. This lack of training resulted in a large number of preventable traffic deaths and accidents.
Read more about this topic: Commercial Driver's License