the average speed of the city's public transit was approximately 8.5 miles per hour – slightly faster than the average speed of 8.1 in 2007. Muni soon started on a large building program. On December 29, 1914, the new Stockton Street Tunnel under Nob Hill opened, allowing streetcars from downtown to go to North Beach and the new Marina District. On February 3, 1918, the Twin Peaks Tunnel opened, making the southwestern quarter of the city available for development. On October 21, 1928, the Sunset Tunnel opened, bringing the N Judah streetcar line to the Sunset District. These improvements plunged Muni into direct competition with the URR on the entire length of Market Street. The two operators each operated its own pair of tracks down that thoroughfare, which came to be known as the "roar of the four". 1940s: The first trolleybuses In 1941, Muni introduced its first trolleybus line, the R-Howard line. Trolleybuses had been running in San Francisco since 1935, but operated only by the Market Street Railway Company (MSRy), successor to the URR. By 1944, the MSR was in financial difficulties. Thus, at 5 am on September 29, 1944, Muni acquired its commercial competitor. Along with the routes and equipment, Muni adopted its competitor's more expensive seven-cent fare. Following national trends, Muni replaced most of its rail lines with trolleybus service in the succeeding decades. A few lines with dedicated rights-of-way (including those serving the Twin Peaks and Sunset tunnels) continued as rail lines running 1940s-era PCC streetcars through the 1970s. These lines became the foundation of the Muni Metro. During World War II, because male employees had been called to serve in the military, both MSRy and Muni hired female 'motorettes' and conductors, including poet and author Maya Angelou in 1943. 1970s and 1980s: Construction and reorganization In the 1950s and 1960s, the regional BART system was conceived as a much more extensive system than was eventually built, with plans for express trains through San Francisco and local service within San Francisco. Because it was assumed BART would provide local rail service, investment in Muni infrastructure failed to keep pace with major urban redevelopment projects. For example, BART was intended to provide Richmond district and Western Addition service as part of its Golden Gate Bridge/Marin line. This leaves a legacy of the inadequate 38-Geary bus serving these neighborhoods. Construction on BART's Market street tunnel started in