The quick answer is all of the regulations apply, but is also dependent upon the type of operation you are engaged in and the size and type of vehicles you operate. Typically, the regulations dealing with driver qualifications such as medical certificate or medical waiver; vehicle markings; vehicle equipment such as required braking equipment for any trailers pulled, steering, suspension, tires, load securement and emergency equipment; drivers' hours of service and record of duty status; and vehicle inspection and maintenance.