If you’re going to spend $30 million or more to carry vehicles across a relatively short span of water, you might as well do other interesting things with the structure.
That’s the idea behind the Memorial Bridge that connects Portsmouth, N.H, with Kittery, Maine. across the mouth of the tidal Piscataqua River. (Note: This is not the Piscataquog River, which is in a different watershed about 50 miles away but still in New Hampshire. That’s not confusing at all.)
When it became obvious that the old bridge needed to be replaced, UNH engineers worked with the design and created the Living Bridge Project, which incorporates a bunch of sensors that monitor the condition of the bridge, as well as the estuary, and a small tidal turbine to help power them.
It’s got a nice write-up here at EOS.