The funds generated under the authority of Chapter 36.73 RCW shall be used for transportation improvements that construct, preserve, maintain and operate the existing transportation infrastructure of the city, consistent with the requirements of Chapter 36.73 RCW. The funds may be utilized for any lawful purpose under the chapter; but all funds raised pursuant to the chapter shall be expended only for such preservation, maintenance and operation in accordance with the provisions of Chapter 36.73 RCW as the same exists or is hereafter amended. The funds expended by the city shall construct, preserve, maintain and operate the city’s previous investments in the transportation infrastructure, reduce the risk of transportation facility failure, improve safety, continue the cost-effectiveness of the city’s infrastructure investments, and continue the optimal performance of the transportation system. Additional transportation improvement projects may be funded only after compliance with the provisions of RCW 36.73.050(2)(b) following notice, public hearing and enactment of an authorizing ordinance.