joined by twelve other proposed projects to cross the Bay in October 1921, several of which featured rail service through long tunnels. In 1947, a joint Army-Navy Commission recommended an underwater tube as a means of relieving automobile congestion on the then-ten-year-old Bay Bridge. The recommendation was issued in a report undertaken to determine the feasibility of the Reber Plan. Construction Seismic studies commenced in 1959, including boring and testing programs in 1960 and 1964, and the installation of an earthquake recording system on the Bay floor. The tube's route was modified after preliminary surveys were unable to identify a continuous bedrock profile, requiring more precise boring and probing of the Bay floor. The route was deliberately chosen to avoid bedrock as much as possible so the tube was free to flex, avoiding concentrated bending stresses. Design concepts and route alignment were completed by July 1960. A 1961 report estimated the cost of the Transbay Tube at . Construction was started on the tube in 1965, and the structure was completed after the final section was lowered on April 3, 1969. BART sold commemorative bronzed aluminum coins to mark the placement of the final section. Prior to being fitted out, the tube was opened for visitors to walk through a small portion on November 9, 1969. The tracks and electrification needed for the trains were finished in 1973, and the tube was opened to service on September 16, 1974, five years after the originally-projected completion date, after clearing California Public Utilities Commission concerns regarding the automated dispatch system. The first test run was performed by a train under automatic control on August 10, 1973. Train No. 222 ran from to in seven minutes at and returned in six minutes at the full speed of , carrying approximately 100 passengers including BART officials, dignitaries and reporters. The tunnel is set in a trench wide with a gravel foundation deep. Lasers were used to guide the dredging of the trench and the laying of the gravel foundation, maintaining route accuracy of within for the trench and for the foundation. Construction of the trench required dredging of material from the Bay. The structure is made of 57 individual sections that were built on land at the Bethlehem Steel shipyard on Pier 70 and towed out into the bay by a large catamaran barge. After the steel shell was completed, water-tight bulkheads were fitted