Even on the most idyllic sunny day on the San Mateo County coast, it's chilly, dark, dusty, muddy and noisy deep inside San Pedro Mountain, where construction crews are digging twin tunnels to carry traffic around Devil's Slide. But despite the gloomy atmosphere, workers are making major progress on the $325 million tunnel project, which includes a pair of arched bridges and an operations center. The buildings and the bridges are finished, and the tunnel diggers are expected to bust through the north end of the mountain by this fall. A little more than a year later, the finished tunnel...