Scottsdale has a main branch and four branches within the Scottsdale Public Library System. State Route 101 – locally known as Loop 101 – provides convenient Metropolitan Phoenix Freeways access. The city is home to Scottsdale Municipal Airport , a single-runway airport located in North Scottsdale. While the airport serves some tour and commuter flights, the plurality of aircraft operations are corporate and transient general aviation traffic. Commercial air travel is served by Phoenix Sky Harbor International Airport in Phoenix and Phoenix Mesa Gateway Airport in Mesa. Public bus service for Scottsdale and the Phoenix Metropolitan Area is provided by Valley Metro. The city of Scottsdale runs a network of local neighborhood circulators, labeled the "Scottsdale Trolley." Using trolley-replica buses, the public service is free to riders. There are currently two circulating "routes," known individually as the Downtown Trolley and the Neighborhood Trolley. These connect at the Loloma Station transit center in downtown Scottsdale. The Downtown Trolley circulates through downtown Scottsdale, and the Neighborhood Trolley circulates from downtown Scottsdale to neighborhoods throughout South Scottsdale, connecting with the city of Tempe's own free public circulator, the Tempe Orbit at Roosevelt and Scottsdale Road. From there, riders can transfer onto the Tempe Orbit, and travel to Tempe, including Arizona State University's main campus, and the downtown Tempe, or Mill Avenue, area. Between December 2007 and 2009, Scottsdale was a member of the board of Valley Metro Rail line which connects the neighboring cities of Phoenix, Tempe and Mesa. There was a study in 2001, and some discussion since, of extending the light rail line into Scottsdale. The city's Transportation Master Plan identifies Scottsdale Road as the city's high-capacity corridor, which could be light rail, modern streetcar service, or bus rapid-transit (BRT). A street railway interurban line was proposed to connect Scottsdale with Phoenix, Tempe, and Mesa as early as 1913 but was never built; Scottsdale is the largest American city that has never had a rail line.