The secondary state highway system shall consist of all of the public highways, causeways, bridges, landings, and wharves in the counties of the Commonwealth not included in the primary state highway system. The secondary state highway system shall include such highways and community roads leading to and from public school buildings, streets, causeways, bridges, landings, and wharves in towns having a population of 3,500 or less according to the United States census of 1920, and in all towns having such a population incorporated since 1920, that constitute connecting links between highways in the secondary state highway system in the counties and between highways in the secondary state highway system and highways in the primary state highway system, not to exceed two miles in any one town. If in any such town that is partly surrounded by water less than two miles of the highways and streets therein constitute parts of the secondary state highway system, the Board shall, upon the adoption of a resolution by the governing body of such town designating for inclusion in the secondary state highway system certain highways and streets in such town not to exceed a distance of two miles, less the length of such highways and streets in such town that constitute parts of the secondary state highway system, accept and place in the secondary state highway system such additional highways and streets.