I don't know how relevant this idea would be in the US but in Europe it's very relevant due to the number of low bridges.
Have you ever seen a truck stuck under a bridge or crash into a bridge that was too low for the height of the truck? Well here's my idea.
Have a 2 part device that's attached to the roof of the truck cab. The first part of device scans the height of the trailer or whatever is being carried on the trailer. The second part of the device scans forward to detect low bridges etc. A small chip in the cab then determines if the bridge is too low for the trailer and sounds an alarm if it is.
This might sound like a ridiculous idea to some, but I have seen 3 different trucks get stuck under bridges that are too low, and that's within the last 4 years in my own hometown.
Reward: Money, and lots of it.