SAO PAULO—Part of a major expressway collapsed on Tuesday above a construction site in the Brazilian city of Sao Paulo where Spain’s Acciona SA. was excavating a tunnel for a new subway line. No casualties were reported, but it was the latest setback for a much-delayed project that has become a symbol of dysfunctional public construction in Latin America’s largest economy. Television images showed a lane of the Marginal Tiete expressway caving into a widening pit alongside the construction site of the tunnel under a nearby river for the planned Line 6. The Sao Paulo state metro operator said on its website that tunnels dug for the new subway project had been flooded. Public safety officials said all 50 workers were able to exit the tunnel and only two were treated for contact with dirty water that gushed through the site. There was conflicting information as to what caused the …