Regional Transportation District

The Regional Transportation District, more commonly referred to as RTD, is the regional agency operating public transit services in all or a portion of eight counties (six of the ten counties in the Denver-Aurora-Centennial, CO Metropolitan Statistical Area, plus Boulder County and Weld County, but not Elbert County, Park County, Clear Creek County, or Gilpin County) in the U.S. state of Colorado. It operates over a 2,349-square-mile (6,080 km2) area, serving 3.09 million people.

Source: Wikipedia — Regional Transportation District (CC BY-SA 4.0)