The Sacramento Regional Transit District, commonly referred to as RT, is the agency responsible for public transportation in the Sacramento, California area. It was established on April 1, 1973, as a result of the acquisition of the Sacramento Transit Authority. In addition to operating over 60 bus routes with connecting bus service in the Sacramento area covering ., RT also operates a large light rail system. It is currently the eleventh busiest light rail system in the United States. In addition to the city of Sacramento, RT serves much of the northern portion of Sacramento County which includes the incorporated cities of Citrus Heights and Rancho Cordova. The unincorporated areas of Sacramento County under the RT service area include Arden Arcade, Carmichael, Fair Oaks, Florin, Gold River, North Highlands, Orangevale, Rio Linda and Rosemont. The system formerly provided express bus service between Downtown Sacramento and Elk Grove until the mid-2000s when that city took over bus operations under the newly created E-tran. It also provided contracted bus service to neighboring Yolo County (covering West Sacramento, Davis and Woodland); those routes and operations were later taken over by Yolobus after its formation on January 3, 1982. In both cases, e-tran and Yolobus have retained the RT assigned route numbers for their routes as they continue to service Downtown Sacramento.