Bridge four-lane highway on the upper level and a pair of railway tracks at the lower level. Tower Bridge in London is different example of a double-decked bridge, with the central section consisting of a low level bascule span and a high level footbridge. A viaduct is made up of multiple bridges connected into one longer structure. The longest and some of the highest bridges are viaducts, such as the Lake Pontchartrain Causeway and Millau Viaduct. A three-way bridge has three separate spans which meet near the center of the bridge. The bridge appears as a "T" or "Y" when viewed
Grand Tower Pipeline Bridge out across the river where welders connected them together. Each pipe weighs 5 tons and it took 72 pipes to span the river, adding to around 360 tons of dead weight. The abutments to support this weight go to the bedrock, 50 feet deep on the Illinois side and 154 feet on the Missouri side. The site at Grand Tower/Wittenberg was chosen because the river is narrow and deep there, and the limestone bedrock could be easily reached. Grand Tower Pipeline Bridge The Grand Tower Pipeline Bridge is a suspension bridge carrying a natural gas pipeline across the Mississippi River