What is twin spans?

Twin spans refer to a pair of bridges or spans constructed parallel to each other, typically crossing over a body of water or a valley. These two bridges are usually built to provide safe and efficient transportation for vehicles and pedestrians, especially in high traffic areas. Twin spans may also provide an emergency alternative if one bridge becomes damaged or closed due to natural disasters or accidents. Examples of famous twin spans include the Lake Pontchartrain Causeway in Louisiana and the Golden Gate Bridge in San Francisco, which has two parallel roadway decks.