eli5: Why do some waterways have bridges and others have tunnels?
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Some foods are easier to eat with a fork, others with a spoon. It’s the same thing with waterways: sometimes the best solution is a bridge, other times a tunnel. A few examples of bridge vs. tunnel questions are:
– How deep is the water? If it’s shallow, that makes it easier to build a bridge. If it’s deep and narrow, a suspension bridge might work (one tower on each side, hang the bridge in between the two towers). If it’s deep and wide, the best option is usually a tunnel.
– Is the waterway a shipping route? If it is, the bridge needs to be tall enough for them – or you can skip the problem and add a tunnel. A lot of crossings use bridges and tunnels, like the Øresund crossing between Sweden and Denmark and the Chesapeake Bay bridge-tunnel in Virginia.
– Are there high winds and/or icy weather in the area? Some bridges have to partially or completely close when the winds are too strong or the bridge is freezing. In those cases, a tunnel is more reliable.
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