The elevenfooteight bridge now has a traffic light which goes red and stays red on detecting an overheight vehicle, with a lit-up sign saying "OVERHEIGHT MUST TURN". It's still getting hit by overheight vehicles.
And then there's the lengths that had to be gone to in Syndey to stop overheight vehicles entering tunnels:
The 11'8 bridge does indeed seem a lost cause as far as preventing people from ruining their overheight vehicles. But the problem for the bridge has been solved: they installed a beam in front of the bridge which takes the impact.
The same sort of thing could be done with this bridge. Install a sturdy beam ahead of the structural bits. You won't stop people from driving overheight vehicles onto the bridge, but you will stop them from destroying the bridge in the process.
I guess you could have a mechanism to raise the warning beam and only activate it after direct communication with the driver.
That's sort of the other way of looking at the problem. The bridge isn't overbuilt enough.