Crist offers practice exams for the written portion of its CDL test for free through its website at http://www.cristcdl.com/otc/. These practice tests cover general knowledge, air brakes, hazardous material, passengers, tankers and doubles/triples. There are also three practice combination tests.
Be aware that individual state laws and regulations sometimes supersede the answers given in the Crist practice tests. Be sure to check with your state CDL booklet if you are unsure of any answers on the test. State CDL rule booklets are available through the Department of Motor Vehicles or the state's Department of Highway Safety. Good luck on your test.