Caltrans engineer Bunma Nou walks in a trench above the southbound main post tunnel, where Halleck Street will eventually link the center of the Presidio to Crissy Field, as the Presidio Parkway construction project nears completion in San Francisco, Calif. on Wednesday, May 6, 2015. Caltrans will shut down the roadway for an extended weekend to reroute traffic to the permanent configuration in both northbound and southbound directions.