Jigger,
I understand he's not supposed to be there. But building a bridge purposely low is a technique that was popular until the 1970s and is now long gone.
No matter how low you make your bridge, you'll always stupid truckers driving into them. The modern take on the problem is you raise the bridges so you dont get stupid accidents (which are huge problems on busy freeways) and increase law enforcement. Keep police patrols and fine truckers a huge sum if they're not supposed to be where they are. That way you dont risk lives, clog up traffic, waste public resources cleaning up the mess, or have insurance companies dealing out unnecessary claims.