Under Southern Pacific the line was double tracked in 1904, and multiple cutoffs were built over a period ending in 1910. The first of these, the Bayshore Cutoff, opened in 1907 and rerouted the line through a series of five tunnels built along the shoreline of San Francisco Bay. This saved approximately three miles and seventeen minutes compared to the prior route, which veered to the west around San Bruno Mountain. The Bayshore Cutoff also eliminated the use of helper engines to bring trains over the mountain. The second, the Mayfield Cutoff, opened in 1908 to provide service to western Santa Clara Valley cities such as Los Altos and Los Gatos. The third, the Dumbarton Cutoff, opened in 1910 and included the first bridge across San Francisco Bay, between Newark and Menlo Park, saving many miles to Oakland and Sacramento compared to the prior route through San Jose and Santa Clara.