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"A frequently cited rule-of-thumb in transportation engineering is that tunnel construction costs two to three times as much as bridges, and that simple rule of thumb explains why there are so many more bridges than tunnels in operation today."

What gives you your understanding? Mine is from multiple sources at the top of Google for the query "price of tunnel versus price of bridge"

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I’ve never said it was the same. Somewhat comparable. In practice bridge is likely more expensive, if you take in the externalities accumulated over the lifespan of the bridge full of cars.

Engineering costs its a matter of volume, what kind of ground you need to dig, expertise and experience. If you can get something like the Boring company up, costs would drop down.

And engineering costs don’t account for externalities of having a bridge full of noisy cars hanging there, polluting in every modality: view, noise, smell, splitting the neighborhood, reducing walkability, destroying the property value.

The bridge is literally on top of a bunch of faults. Tunnels are even more of a death trap. No thanks.

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