coming on board before Muni started its next full diesel fleet replacement cycle in 1999. This was fourteen years after the previous cycle instead of the twelve years that buses are designed to last. Muni is now aware that they must expect to keep diesel buses past their design life and have also found that funds granted for mid-life rebuilds require that the buses be kept longer still. As the fleet replacement cycle begins again in 2013, Muni has arranged for life-extending rebuilds of 142 buses, by count over 30% of the fleet. In September 1982, the cable car system was shut down for 21 months for rebuilding, and there were massive line reorganizations as Muni restructured their route network to provide stronger cross-town services. In 1983, Muni temporarily ran streetcars down Market Street as part of the San Francisco Historic Trolley Festival, initially conceived of as a substitute attraction for tourists during the one summer when no cable cars would be in operation. The service became so popular that the festival was repeated for several years following. Anticipating the return of permanent streetcar service on Market Street, Muni began rehabilitating tracks in 1987, a process that culminated in the opening of the F line in 1995. The first modern Muni shelter was installed in front of the War Memorial Opera House in 1987. 1990s: the "Muni Meltdown" The F line was reintroduced in 1995 as a heritage streetcar service. Initially designed as a temporary tourist attraction to make up for the suspension of cable car service for rebuilding, the F has become a permanent fixture. E line service, initially known as the Muni Metro Extension, started in January 1998 initially as a shuttle between Embarcadero station and Caltrain's 4th and Townsend station. In June 1995, the San Francisco County Transportation Authority released The Four Corridor Plan, a vision to extend Muni Metro service along four major routes in the city: Bayshore (north-south along Third from the county line to California), Geary (east-west along Geary from 48th to Market/Kearny), North Beach (extending the new north-south Bayshore line along Kearny and Columbus to Fisherman's Wharf), and Van Ness (north-south along Van Ness from 16th and Mission to Aquatic Park), with a connector downtown to transfer between the Bayshore, Geary, and North Beach corridors. These have since been implemented as a combination of light rail (T Third and Central Subway) and bus