49 U.S. Code § 14102. Leased motor vehicles
(a) General Authority of Secretary.—The Secretary may require a motor carrier providing transportation subject to jurisdiction under subchapter I of chapter 135 that uses motor vehicles not owned by it to transport property under an arrangement with another party to—
make the arrangement in writing signed by the parties specifying its duration and the compensation to be paid by the motor carrier;
carry a copy of the arrangement in each motor vehicle to which it applies during the period the arrangement is in effect;
inspect the motor vehicles and obtain liability and cargo insurance on them; and
(b) Responsible Party for Loading and Unloading.—
The Secretary shall require, by regulation, that any arrangement, between a motor carrier of property providing transportation subject to jurisdiction under subchapter I of chapter 135 and any other person, under which such other person is to provide any portion of such transportation by a motor vehicle not owned by the carrier shall specify, in writing, who is responsible for loading and unloading the property onto and from the motor vehicle.