Right out of the federal rules section:
(Personally I like the one about transporting human corpses but that opens up a whole new argument thread.)
(BTW, Ohio law has the same exemptions for transporting your own things (#3) and it follows federal law.)
§ 390.3General applicability.
(a) The rules in subchapter B of this chapter are applicable to all employers, employees, and commercial motor vehicles, which transport property or passengers in interstate commerce.
(b) The rules in part 383, Commercial Driver's License Standards; Requirements and Penalties, are applicable to every person who operates a commercial motor vehicle, as defined in §383.5 of this subchapter, in interstate or intrastate commerce and to all employers of such persons.
(c) The rules in part 387, Minimum Levels of Financial Responsibility for Motor Carriers, are applicable to motor carriers as provided in § 387.3 or § 387.27 of this subchapter.
(d) Additional requirements. Nothing in subchapter B of this chapter shall be construed to prohibit an employer from requring and enforcing more stringent requirements relating to safety of operation and employee safety and health.
(e) Knowledge of and compliance with the regulations. (1) Every employer shall be knowledgeable of and comply with all regulations contained in this subchapter which are applicable to that motor carrier's operations.
(2) Every driver and employee shall be instructed regarding, and shall comply with, all applicable regulations contained in this subchapter.
(3) All motor vehicle equipment and accessories required by this subchapter shall be maintained in compliance with all applicable performance and design criteria set forth in this subchapter.
(f) Exceptions. Unless otherwise specifically provided, the rules in this subchapter do not apply to—
(1) All school bus operations as defined in §390.5, except for the provisions of §§ 391.15(f), 392.80, and 392.82 of this chapter.
(2) Transportation performed by the Federal government, a State, or any political subdivision of a State, or an agency established under a compact between States that has been approved by the Congress of the United States;
(3) The occasional transportation of personal property by individuals not for compensation nor in the furtherance of a commercial enterprise;
(4) The transportation of human corpses or sick and injured persons;
(5) The operation of fire trucks and rescue vehicles while involved in emergency and related operations;
(6) The operation of commercial motor vehicles designed or used to transport between 9 and 15 passengers (including the driver), not for direct compensation, provided the vehicle does not otherwise meet the definition of a commercial motor vehicle, except that motor carriers and drivers operating such vehicles are required to comply with §§390.15, 390.19, 390.21(a) and (b)(2), 391.15(f), 392.80 and 392.82 of this chapter.
(7) Either a driver of a commercial motor vehicle used primarily in the transportation of propane winter heating fuel or a driver of a motor vehicle used to respond to a pipeline emergency, if such regulations would prevent the driver from responding to an emergency condition requiring immediate response as defined in § 390.5.