When a rural district council considers that a highway in its district ought to become a main road by reason of its being a medium of communication between great towns, or a thoroughfare to a railway station, or otherwise, it may apply to the county council for an order "maining" the road under s. 15 of the Highways and Locomotives (Amendment) Act, 1878 (41 & 42 Vict. c. 77), as amended by s. 3 (viii.) of the Local Government Act, 1888 (51 & 52 Vict. c. 41), and the county council may make an order accordingly.