The city council may, by resolution, establish decreased speed limits when, on the basis of an engineering and traffic survey, it determines that a speed limit of fifty-five (55) miles per hour is more than is reasonable or safe on any part of a street or highway when such speed limit is fifty-five (55) miles per hour under the California Vehicle Code and further determines that a speed of fifty (50), forty-five (45), forty (40), thirty-five (35), thirty (30) or twenty-five (25) miles per hour is more appropriate to facilitate the orderly movement of vehicular traffic. The limits shall be effective when appropriate signs giving notice thereof have been erected. (Prior code § 3002.3)