[3] The creation of the RapidRide network was one of the main elements of King County's "Transit Now" initiative that was proposed in April 2006 and approved by voters in November 2006.

[4] Funding for the construction and operation of the lines came from a 0.1% sales tax increase included in Transit Now, contributions from local cities and over $80 million in grants from state and federal agencies.

[5] One of the most notable local contributions was from Seattle, which funded traffic signal and roadway improvements with the city's "Bridging the Gap" property tax levy, passed at the same time as Transit Now in November 2006.

To combat the loss of income Metro underwent a series of efficiency measures, including restructuring routes to reduce operating costs.

The RapidRide system was largely shielded from these cuts because federal and state grant funding helped pay for new buses and infrastructure.

[8] Next up were the RapidRide corridors in Seattle, but the nationwide economic downturn forced Metro to create a lower cost routing than was proposed in the Transit Now measure.

This interline was finally broken in March 2016 after the passage of Proposition 1 in the City of Seattle, dedicating additional tax revenue to support the Metro system.

After several months of outreach by the Seattle Department of Transportation, it was decided that the C Line would serve the Alaska Junction (a major transfer point for buses), the Fauntleroy ferry terminal and Westwood Village.

The opening of the new lines (along with budget cuts forced by the economic downturn) prompted a substantial restructuring of Metro's system in Seattle.

[15] In late 2009, the construction of a sixth line was added to the system that would run between Burien and Renton in South King County.

The D Line was extended to its original planned terminus in Pioneer Square, connecting riders better to South Downtown employment sites and visitors attractions.

The C Line was extended into the vastly growing Denny Triangle and South Lake Union areas using new transit priority lanes on Westlake Avenue.

[20][21][22] The network will create a grid of frequent bus lines connecting the major population centers in King County.

In many cases, the opening of the routes is timed to coincide with the expansion of Sound Transit's Link light rail system.

Stops are farther apart than typical Metro service in order to increase speed and reliability,[3] and create "stations"[3] that are akin to what is found on light rail lines.