Federal regulation 23 C.F.R. § 460.2 (c) defines a public road as follows:
 “A road will be open to public travel; a road section must be available, except during scheduled periods, extreme weather or emergency conditions, passable by four-wheel standard passenger cars, and open to the general public for use without restrictive gates, prohibitive signs, or regulation other than restrictions based on size, weight or class of registration. Toll plaza of public toll roads are not considered restrictive gates.”