In this subchapter—

(1) “commercial motor vehicle” means (except in section 31106) a self-propelled or towed vehicle used on the highways in commerce principally to transport passengers or cargo, if the vehicle—

(A) has a gross vehicle weight rating or gross vehicle weight of at least 10,001 pounds, whichever is greater;

(B) is designed to transport more than 10 passengers including the driver; or

(C) is used in transporting material found by the Secretary of Transportation to be hazardous under section 5103 of this title and transported in a quantity requiring placarding under regulations prescribed by the Secretary under section 5103.

(2) “employee” means a driver of a commercial motor vehicle (including an independent contractor when personally operating a commercial motor vehicle), a mechanic, a freight handler, or an individual not an employer, who—

(A) directly affects commercial motor vehicle safety in the course of employment by a commercial motor carrier; and

(B) is not an employee of the United States Government, a State, or a political subdivision of a State acting in the course of employment.

(3) “employer”—

(A) means a person engaged in a business affecting commerce that owns or leases a commercial motor vehicle in connection with that business, or assigns an employee to operate the vehicle in commerce; but

(B) does not include the Government, a State, or a political subdivision of a State.

(4) “State” means a State of the United States, the District of Columbia, Puerto Rico, the Virgin Islands, American Samoa, Guam, and the Northern Mariana Islands.