I wonder if they focus grouped the signage ? To me it seemed clear, but now that you point it out... I see where the confusion could happen!
The truck driver doesn't realize the sign is only on when he is there, he never sees it when it's off, he has no idea it's illuminated specially for him.
This is government saying "We did something", while doing nothing.
And this sign is above even the traffic lights. Even someone glancing at the colors would not see this.
What they should do is lower the sign to the height of the bridge - so people hit the sign (or something dangling from it).
But that would require government admitting that people hitting the bridge is their fault, and not stupid drivers.