People in the San Francisco Bay Area rely on a complex multimodal transportation infrastructure consisting of roads, bridges, highways, rail, tunnels, airports, seaports, and bike and pedestrian paths. The development, maintenance, and operation of these different modes of transportation are overseen by various agencies, including the California Department of Transportation (Caltrans), the Association of Bay Area Governments, San Francisco Municipal Transportation Agency, and the Metropolitan Transportation Commission. These and other organizations collectively manage several interstate highways and state routes, eight passenger rail networks, eight trans-bay bridges, transbay ferry service, local and transbay bus service, three international airports, and an extensive network of roads, tunnels, and bike paths. The Bay Area, especially San Francisco, are frequently listed as one of the best and most extensive cities and/or metropolitan areas in the United States for public transportation. Local trips on transit are frequently accomplished by bus services. Different agencies serve different corners of the Bay Area, such as samTrans serving mostly San Mateo County and County Connection connecting the suburbs of Contra Costa County; though some bus agencies operate transbay services, such as Golden Gate Transit. While ferries also connect communities across the bay, most transbay and longer-distance trips on public transportation, however, use rail-based transit. Bay Area Rapid Transit (BART) is the sole heavy rail system within the bay and the dominant provider of regional transportation between San Francisco, northern San Mateo County, and much of the East Bay. The Bay Area is also home to various commuter rail services, such as SMART within Sonoma and Marin counties, Caltrain on the San Francisco Peninsula, ACE between San Jose and Stockton, and various Amtrak routes out of Oakland and San Jose. San Francisco is also the home of the world's last manually-operated cable car system, and both San Francisco's SFMTA and Santa Clara's VTA operate light rail networks to complement their bus services. With the sole exception of ACE and Amtrak services, all public transit within the Bay Area can be paid for by using the Clipper card. Though not as extensive as Southern California's freeways, the Bay Area is also home to an extensive network of highways. Four bridges traverse the San Francisco Bay itself and four more traverse the northern San Pablo Bay, in addition to more localized expressways such as US 101 and Interstate 280 in the Peninsula, Interstates 680 and 880 in the East Bay, and Interstate 505