36 CFR § 4.21 - Speed limits.
(a)Park area speed limits are as follows:
(1) 15 miles per hour: within all school zones, campgrounds, picnic areas, parking areas, utility areas, business or residential areas, other places of public assemblage and at emergency scenes.
(2) 25 miles per hour: upon sections of park road under repair or construction.
(3) 45 miles per hour: upon all other park roads.
(b) The superintendent may designate a different speed limit upon any park road when a speed limit set forth in paragraph (a) of this section is determined to be unreasonable, unsafe or inconsistent with the purposes for which the park area was established. Speed limits shall be posted by using standard traffic control devices.
(c) Operating a vehicle at a speed in excess of the speed limit is prohibited.
(d) An authorized person may utilize radiomicrowaves or other electrical devices to determine the speed of a vehicle on a park road. Signs indicating that vehicle speed is determined by the use of radiomicrowaves or other electrical devices are not required.