Withstand ship collisions and high winds.
A bridge the size and configuration of Gibraltar Bridge is usually protected by artificial islands built around its piers. That way, ships run aground before they can do any damage to the structure.
But artificial islands are not an option in the middle of the ocean. The Gibraltar Bridge designers instead envision a ring of underwater bumpers to withstand ship collisions.
Build in the open ocean.
When determining the exact site of the bridge, designers had to choose between a shallow area that spanned 20 miles, which would have meant many piers in a busy shipping zone, and a narrow portion that's 2,700 feet deep.
But the Gibraltar Bridge designers lucked out.
A closer inspection of the narrow portion revealed an underwater "mountain" in the center that could hold the center piers, dividing the bridge into two spans of 4 1/2 miles each.
Gibraltar Bridge — if stretched over NYC
Span 9 Miles
The longer the span, the heavier the bridge.
At the length required to span the Strait of Gibraltar
, a suspension bridge that supports the weight of the roadway with cables spanning from tower to tower would sag and ultimately collapse.