36 C.F.R. § 4.22 : Parks, Forests, and Public Property — NATIONAL PARK SERVICE, DEPARTMENT OF THE INTERIOR — VEHICLES AND TRAFFIC SAFETY — Unsafe operation

(a) The elements of this section constitute offenses that are less serious than reckless driving. The offense of reckless driving is defined by State law and violations are prosecuted pursuant to the provisions of section 4.2 of this chapter.
(b) The following are prohibited:
(1) Operating a motor vehicle without due care or at a speed greater than that which is reasonable and prudent considering wildlife, traffic, weather, road and light conditions and road character.
(2) Operating a motor vehicle in a manner which unnecessarily causes its tires to squeal, skid or break free of the road surface.
(3) Failing to maintain that degree of control of a motor vehicle necessary to avoid danger to persons, property or wildlife.
(4) Operating a motor vehicle while allowing a person to ride:
(i) On or within any vehicle, trailer or other mode of conveyance towed behind the motor vehicle unless specifically designed for carrying passengers while being towed; or
(ii) On any exterior portion of the motor vehicle not designed or intended for the use of a passenger. This restriction does not apply to a person seated on the floor of a truck bed equipped with sides, unless prohibited by State law.

36 C.F.R. §4.22