[5] The Southwest Washington Regional Transportation Council (RTC) completed a two-year planning effort to develop a high-capacity transit system for Vancouver and Clark County in 2008.

[8] C-Tran, Clark County's transit agency, pursued developing the routes in order of highest ridership and adopted a 20-year plan recommending the first BRT line on Fourth Plain Boulevard.

[10] Early design and public outreach for the Mill Plain BRT project began in 2018,[11][12] and four alignment options were presented.

[5][16] C-Tran broke ground for the Mill Plain BRT project on September 28, 2021, at the parking lot behind the Clark College Columbia Tech Center building, the eventual site of the line's eastern terminus.

[17] A ribbon-cutting ceremony at the same site was held on September 30, 2023; regular service on the Red Line began the following day.