Whenever the state traffic commission shall determine that any prima facie limit set forth in § 31-14-2 is greater than is reasonable in any historic district listed on the National Register of Historic Places or on any road duly recognized as a scenic highway by the scenic highway board in accordance with the provisions of chapter 14 of title 24, the commission shall determine and declare a reasonable and safe prima facie limit, in the manner set forth in § 31-14-4, in order to provide for the preservation of the historical character of the district or the scenic quality of the highway, provided that:
R.I. Gen. Laws § 31-14-4.1