Cycling is popular in Tucson due to its flat terrain and dry climate. Tucson and Pima County maintain an extensive network of marked bike routes, signal crossings, on-street bike lanes, mountain-biking trails, and dedicated shared-use paths. The Loop is a network of seven linear parks comprising over 100 mi (160 km) of paved, vehicle-free trails that encircles the majority of the city with links to Marana and Oro Valley. The Tucson-Pima County Bicycle Advisory Committee (TPCBAC) serves in an advisory capacity to local governments on issues relating to bicycle recreation, transportation, and safety. Tucson was awarded a gold rating for bicycle-friendliness by the League of American Bicyclists in 2006.