for adults and $1.25 for youth ages 5–17, seniors, and the disabled. Muni currently operates a Free Muni for Seniors program that provides low- and moderate-income seniors residing in San Francisco free access to all Muni transit services, including Muni's cable cars. Free Muni is open to all San Francisco senior Clipper card holders, ages 65 and over, with a gross annual family income at or below 100 percent of the Bay Area median income level (qualifying income levels are posted on the program's web page). Enrollment is not automatic. To participate in the program, a qualified senior must have or obtain a Clipper card and submit an application either online or by mail. Like Muni buses, the Muni Metro operates on a proof-of-payment system; on paying a fare, the passenger will receive a ticket good for travel on any bus, historic streetcar, or Metro vehicle for 120 minutes. Payment methods depend on boarding location. On surface street sections in the south and west of the city, passengers must board at the front of the train and pay their fare to the train operator to receive their ticket; those who already have a ticket, or who have a daily, weekly, or monthly pass, can board at any door of the Metro streetcar. Subway stations have controlled entries via faregates, and passengers usually purchase or show Muni staff a ticket in order to enter the platform area. Faregates closest to an unmanned Muni staff booth open automatically if a passenger has a valid pass or transfer that cannot be scanned. Muni's fare inspectors may board trains at any time to check for proof of payment from passengers. All cars are also equipped with Clipper card readers near each entrance, which riders may use to tag their cards to pay their fare. The cards themselves are then used as proof of payment; fare inspectors carry handheld card readers that can verify that payment was made. In subway stations, riders instead tag their cards on the faregates to gain access to the platforms. See also Market Street Railway and other rail lines operated by MUNI: E Embarcadero line F Market & Wharves line San Francisco cable car system SelTrac, the automated train system used in the Market Street subway Light rail in the United States Streetcars in North America List of United States light rail systems by ridership List of North American light