A tunnel through the East Bay Hills to improve regional traffic circulation was envisioned as early as in the 1860s. The first tunnel, known as the Kennedy Tunnel, was constructed for horse-drawn vehicles and pedestrians. Construction began in the 1870’s, but, because of funding shortages, was not completed until 1903, after which it became known as the Broadway Tunnel. It passed through the Berkeley Hills about 160 to 290 feet above the current Caldecott Tunnels and 320 feet below the top of the ridge. The timber-lined Broadway Tunnel was about 17 feet wide and was built to reduce the danger of accidents to travelers descending the steep grade from the summit of the Berkeley Hills. In 1915, the Broadway Tunnel was improved to accommodate automobiles and trucks. The increase in population and the increasing popularity of the automobile rendered this first facility inadequate by the 1930’s. In 1937, the current twin bores of the Caldecott Tunnel were completed and became the main access between Alameda and Contra Costa Counties. During the 1950’s, when the population of Contra Costa County increased by 37 percent, the need to increase the capacity of the tunnel became apparent. In 1964, a third bore, north of the original two, was opened. The design for the third bore included a preliminary alignment and grading for a future fourth bore to be located north of the third bore.