R.I. Gen. Laws § 31-14-7
Whenever local authorities within their respective jurisdictions determine upon the basis of an engineering and traffic investigation that the prima facie speed permitted under this chapter upon any street or highway outside a business or residence district is greater than is reasonable or safe under the conditions found to exist upon the street or highway, the local authority may determine and declare a reasonable and safe prima facie limit on that street or highway, but in no event less than thirty-five miles per hour (35 mph) and subject to § 31-14-8, which reduced prima facie limit shall be effective at all times or during hours of darkness or at any other times that may be determined when appropriate signs giving notice of the authorized speed are erected upon the street or highway.
R.I. Gen. Laws § 31-14-7