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
Tower Bridge (California) Register of Historic Places. The Tower Bridge replaced the 1911 M Street Bridge in Sacramento, which was originally a swing through-truss railroad bridge. Later, roadway sections were added as cantilevered sections on both sides of the existing rail bridge. Sacramento's population more than doubled between 1910 and 1935, rendering the existing bridge inadequate to handle heavy traffic. In 1933, the city realized that it needed a better crossing over the Sacramento River in case of war. On December 22, 1933, the State of California, Sacramento County, and the Sacramento Northern Railway held a conference to plan the new bridge, with