Tucson's Sun Tran bus system serves greater Tucson with standard, express, regional shuttle, and on-demand shuttle bus service. It was awarded Best Transit System in 1988 and 2005. A 3.9-mile streetcar line, Sun Link, connects the University of Arizona campus with 4th Avenue, downtown, and the Mercado District west of Interstate 10 and the Santa Cruz River. Ten-minute headway passenger service began July 25, 2014. The streetcar utilizes Sun Tran's card payment and transfer system, connecting with <answer>the University of Arizona's CatTran shuttles, Amtrak, and Greyhound intercity bus service</answer>.
What transit systems does Sun Link connect to?
the University of Arizona's CatTran shuttles, Amtrak, and Greyhound intercity bus service