western side of San Francisco, recommended shortening the tunnel proposed by Arnold by moving the western portal to Laguna Honda station, but O'Shaughnessy stated the resulting grade would be too steep. Mayor James Rolph signed the Twin Peaks Tunnel Act in November 1913, rejecting the proposal for a shorter tunnel. Construction and opening The contract for tunnel construction was awarded on November 2, 1914 to the R.C. Storrie Company for and work began on the Twin Peaks Tunnel in December 1914 with an estimated three-year construction schedule for the twin-track bore. Construction was completed thirty-three months later. Funding for the tunnel came from special assessment districts established at the eastern and western ends; the undeveloped western area, approximately , was responsible for 85% of tunnel costs. The eastern approach to the tunnel was built along a parcel purchased by the city approximately long and wide at the end of Market. This right-of-way was also later paved to connect Market with Portola. As originally constructed, the total length of the tunnel is (including approaches) and the highest point of the tunnel is near Laguna Honda station. Sloping down from the peak at Laguna Honda, the tunnel has a maximum grade of 3% from west to east and 1.15% from east to west. Excluding approaches, the tunnel is long. The eastern portion (with the exception of the long Eureka Valley station) of the tunnel uses a double-tube subway structure, and the remainder adopts an arched tube profile. As designed, both sections provide of vertical clearance above the top of the rail; each tube in the double-tube section is wide, and the arched tube is wide at its maximum. The lunette space between the arched roof and flat ceiling of the tube was used as a duct to convey fresh air into the tunnel. One blower was mounted at the west end of the double-tube structure, and the other was at a ventilating shaft deep, located east of the western portal. Excavation of the ventilating shaft required pumping of water per day after a horizontal drift at the bottom of the shaft struck water-bearing sand. Laguna Honda, West Portal, and Eureka Valley stations were constructed using cut-and-cover methods. Laguna Honda station is approximately below grade. The tunnel was excavated simultaneously from the open cuts at each end; initial excavation sank three drifts (one at each side along the springline, and one at the