Perhaps not quite a highway, but it does go through the estuary water when the tide comes in. The road is a turning off the A379 at Aveton Gifford, between Kingsbridge and Plymouth in Devon. It runs along the estuary for about three quarters of a mile and is well worth a visit when the tide is out.
If you visit the local pub, avoid mentioning the name of the village! Residents have very strong views on whether the village name should be pronounced Averton Gifford, Orton Gifford, Averton Jifford, Orton Jifford, just to name a few. However, most agree on A.G.
