Workers on the State Route 180 trench, a little north of downtown Fresno, direct a concrete pump as it pours 300 cubic yards of concrete to create a section of wall. The crews are constructing a box that will carry trains under the highway, a rail spur and the Dry Creek Canal. As that concrete sets, the forms will be moved to another section of the tunnel and the process repeated. Other sections of the tunnel rebar are still being tied in preparation for a concrete pour, while the final step will be to construct a lid to enclose the entire structure. The walls, floor and lid will all consist of solid concrete, five feet thick.