Aerial view of a tugboat pushing a precast concrete tunnel section for the BART system under the San FranciscoOakland Bay Bridge When in position the...
{"Image ImageDescription": "Aerial view of a tugboat pushing a pre-cast concrete tunnel section for the BART system under the San Francisco-Oakland Bay Bridge. When in position, the tunnel section will be lowered to the bay floor. San Francisco, May 1968. (Photo by Dean Conger/Corbis via Getty Images)"}