Span 57
The Twin Span Bridge is located on Interstate 10 in Louisiana. It begins in Orleans Parish and crosses into St. Tammany Parish while spanning Lake Pontchartrain.
The span for a tower Bride is centre to centre distance between the pulleys at both ends of towers
Each of the two towers on the Tower Bridge is 213 ft (65 m) high. The central span of the bridge is 200 ft (61 m) between the towers.
Slidell
Slidell
70ft
span bridge
A bridge's span is the length that crosses the gap.
Either the traditional London Bridge-now transplanted to Arizona(!) or the Tower Bridge, popularily called the London Bridge- as it is in London, this may have inspired the folk song. However the bridge isn"t falling down, it is literally folding up as it is a twin leaf bascule structure. when folded up- ships can pass but pedestrtian traffic is halted. Either span would answer the question.
The Tower Bridge is a combined bascule and suspension bridge.
Tower Bridge is east of London Bridge.