36 CFR 4.13 : Parks, Forests, And Public Property (§ 1.1 To Parts 1601-1699) — (§ 1.1 To Parts 80-199) — National Park Service, Department Of The Interior (§ 1.1 To Parts 80-199) — Vehicles And Traffic Safety (§ 4.1 To § 4.31) — Obstructing traffic.

The following are prohibited:

(a) Stopping or parking a vehicle upon a park road, except as authorized by the superintendent, or in the event of an accident or other condition beyond the control of the operator.

(b) Operating a vehicle so slowly as to interfere with the normal flow of traffic.