Today, the Caldecott Tunnel connects Alameda and Contra Costa Counties, located in the San Francisco Bay Area. The original two bores of this tunnel opened in 1937, the same year as the San Francisco–Oakland Bay Bridge, and changed Contra Costa County from an area of small rural communities into one of growing suburbs. But this was not the first tunnel to connect these counties. The Kennedy Tunnel, opened in 1903, was accessed by steep and winding roads and located several hundred feet above today's tunnel. A third bore of the Caldecott Tunnel was opened in 1964 and a long-awaited fourth bore in late 2013. The tunnels have not been without disaster and tragedy over their hundred-plus years of existence, yet they remain an integral part of the commercial, social, and historic fabric of the region.