A giant traffic jam on the Mississippi River has finally cleared.The main 600-foot lock at Lock & Dam 15 broke on August 15th. Since then, crews have been working 24 hours a day to make repairs. Some river traffic used an auxiliary 360-foot lock, but it was too small to accommodate most towboats and barges, so they’ve been backing up on both sides of the broken lock. The first boat through yesterday was the huge American Queen Riverboat. It docked Sunday for a stay that stretched to three days, while passengers stayed busy at Quad Cities attractions, including riverboat casinos and a dinner theatre.