Wash. Rev. Code § 36.120.190
At the option of the planning committee, and with the explicit approval of the regional transit authority, the participating counties may choose to impose any remaining high capacity transportation taxes under chapter 81.104 RCW that have not otherwise been used by a regional transit authority and submit to the voters a common ballot measure that creates the district, approves the regional transportation investment plan, implements the taxes, and implements any remaining high capacity transportation taxes within the boundaries of the regional transportation investment district. Collection and expenditures of any high capacity transportation taxes implemented under this section must be determined by agreement between the participating counties or district and the regional transit authority electing to submit high capacity transportation taxes to the voters under a common ballot measure as provided in this section. If the measure fails, all such unused high capacity transportation taxes revert back to and remain with the regional transit authority. A project constructed with this funding is not considered a "transportation project" under RCW 36.120.020.
RCW 36.120.190