The retaining wall on the Oakland side is taking shape with its art-deco style design, echoing the style of the first two bores which opened in 1937.
The third bore opened in 1964 when, in a way, planning for this new fourth bore had already begun.
"In 1964, what I'm told is that there was recognition that eventually a fourth bore would be needed and in fact Caltrans had the foresight back in 1964 to acquire the right of way for the fourth bore," Caltrans spokesperson Ivy Morrison said.
It was a dramatic scene in November of last year as the road-header broke through from the east side to the west. But that was just the upper arch of the tunnel. Since then, the rest of the tunnel shape has been excavated, with the last bucket of dirt coming out last Friday.
"We're done digging that's the bottom line," Morrison said.
Now the road bed has to be laid down and all the supporting systems put in, like electrical, ventilation, and seismic monitoring. A new maintenance and operations center will bring high-tech to the Caldecott .
"It will still be staffed with real live people but it will have state of the art equipment for seismic monitoring, heat sensors, motion detectors, and other devices that will provide real time information for tunnel operators," Morrison said.
When preliminary planning for the fourth bore project began in 1998, the cost estimate was $150 million and it was expected to take eight years. If the tunnel opens on time, it will have cost $400 million and taken 16 years.