In this image you can see the first four spans over the Monongahela River. From front to back are: The Fort Pitt Bridge, the Smithfield Street Bridge, the Monongahela River Bridge, or Panhandle Bridge (a rail trestle), and the Liberty Bridge. Just above the Fort Pitt, and standing up next to the riverboats is an old pier for what had been a rail trestle to downtown, back when railroads had trains going in to downtown. For more (a lot more!) about Pittsburgh's bridges and tunnels you can try this site: http://pghbridges.com/index.htm