How often do you need to take refresher courses to maintain your commercial driver's license?

Each state independently determines the length of time for which a commercial driver's license is valid before requiring a refresher course, according to DMV.org. Traffic violations committed by a CDL holder impact the driver's ability to hold a CDL certification, states the Federal Motor Carrier Safety Administration.

For example, in Minnesota, commercial driver's licenses expire every four years on the license holder's birthday, reports the Minnesota Department of Public Safety. In Iowa, a commercial driver's license is valid for five to eight years unless the holder is over 72 years old, in which case it is valid for only two years, states DMV.org.