Wash. Rev. Code § 35.58.110
A metropolitan municipal corporation may be authorized to perform one or more metropolitan functions in addition to those which it previously has been authorized to perform, without an election, in the manner provided in this section. A resolution providing for the performance of such additional metropolitan function or functions shall be adopted by the metropolitan council. A copy of such resolution shall be transmitted by registered mail to the legislative body of each component city and county. If, within ninety days after the date of such mailing, a concurring resolution is adopted by the legislative body of each component county, of each component city of the first class, and of at least two-thirds of all other component cities, and such concurring resolutions are transmitted to the metropolitan council, such council shall by resolution declare that the metropolitan municipal corporation has been authorized to perform such additional metropolitan function or functions. A copy of such resolution shall be transmitted by registered mail to the legislative body of each component city and county and of each special district which will be affected by the particular additional metropolitan function authorized.
RCW 35.58.110
Election required to authorize public transportation function: RCW 35.58.245.