line utilizes infrastructure optimized for trolleybuses along Market Street (the former routing of all downtown streetcar lines before the formation of Muni Metro). Statistics The longest Muni line is the a nighttime-only route that blends several other routes together, while the longest daytime route is the . The shortest route is the peak-hour only at , while the shortest off-peak route is the at . The steepest grade climbed by Muni vehicle is 23.1% by a diesel-electric hybrid bus on the line, 22.8% by a trolleybus on the line and 21% by a cable car on the Powell-Hyde line. The busiest Muni bus corridor is the Geary corridor. The two major routes that operate on the corridor, the and , travel in the east–west direction along the Geary corridor, and has an average speed of only , taking over 50 minutes to travel from the Richmond District to the Transbay Terminal when operating on schedule. As of 2015, the corridor has a total of 55,270 average daily boardings, making it the second busiest transit corridor west of the Mississippi after the Los Angeles Metro Wilshire transit corridor. At Powell and Market Streets and California and Market Streets, three types of rail gauges come within a few hundred feet of each other: Bay Area Rapid Transit's broad gauge (which is underground in the lower level of the Market Street subway), Muni Metro's (also underground in the upper level of the subway), and the San Francisco cable car system's narrow gauge (at street level a few hundred feet away to the north of Market Street in both cases). The F Market and Wharves, a heritage streetcar line, which is also standard gauge, is also present here, at street level on Market Street. The rail lines, however, do not physically intersect. Fleet Muni operates about 1,200 vehicles: 550 diesel-electric hybrid buses, 300 electric trolleybuses, 250 modern light rail vehicles, 50 historic streetcars and 40 cable cars. All vehicles, except for cable cars, are wheelchair accessible. The electricity to run all of Muni's trolleybuses, light rail vehicles, streetcars, and the cable car powerhouse comes from the hydroelectric dam at the Hetch Hetchy Reservoir in Yosemite National Park. All of Muni's current internal combustion buses use diesel-electric hybrid powertrains, fueled with renewable diesel fuel made from bio-feedstock sources, including fats, oils and greases. The combination of hybrid technology and renewable diesel fuel helps reduce fuel