FasTracks is a multibillion-dollar public transportation expansion plan under construction in metropolitan Denver, Colorado, United States. Developed by the Regional Transportation District (RTD), the plan consists of new commuter rail, light rail, and express bus services. Six new light rail, electric commuter rail and diesel commuter rail lines with a combined length of will be constructed under the plan. It expands on previous transportation projects, notably T-REX, and includes 57 new transit stations and stops, 21,000 new parking spaces, of a bus service between Denver and Boulder and the renovation of Denver Union Station as a multi-modal transportation hub. Originally envisioned to cost $4.7 billion and to be completed in 2017, voters in the eight counties that comprise the RTD approved a 0.4 percent sales tax increase in 2004. By 2010, the budget grew to $6.5 billion while projected revenues dropped to $4.1 billion. The project is not expected to be finished until after 2050. Alternative funding sources, such as public-private partnerships, have been sought. The first of the six new lines envisioned in the plan, the West Corridor light rail line to Golden, Colorado, opened for revenue service on April 26, 2013. By mid-2014, construction was underway on the five other rail lines. Two commuter rail lines opened on their long-anticipated dates in 2016: the East Rail Line to Denver International Airport and the portion of the Northwest Rail Line to south Westminster. The I-225 Rail Line through Aurora opened on February 24, 2017, and the Gold Line to Wheat Ridge opened on April 26, 2019. In addition, the North Metro Rail Line to Thornton opened in 2020. Denver Union Station underwent $200 million worth of facility improvements to turn it into the hub for new commuter and light rail lines as well as bus service in downtown Denver. The underground 22-bay bus concourse at Union Station opened on May 11, 2014, while the restaurants, bars, and hotel officially opened July 26, 2014. Progress FasTracks is being funded with federal appropriations, private contributions, and a region-wide sales tax increase. The project was allowed to begin when the sales tax portion of its funding was approved by Denver metro area voters in November 2004. The tax went into effect in January 2005. In 2006, engineering design of the initial segment, the West Rail Line, was begun. By spring of 2006, the environmental impact statements of all other proposed lines were