They ought to make it lower, so it’s most obvious that a truck won’t fit. Make it no more than 2metres, whatever that is in American, so that only cars can go through.
a) The bridge has been hit tons of times, and I don't think anyone in a train has been hurt yet.
b) The bridge is probably a lot stronger than the truck, so while the bridge may take damage and need to be repaired, the damage is probably not enough to harm train traffic.
c) If the bridge is damaged enough to harm train traffic, there's probably not a train coming immediately; any on-route trains can be likely stopped before they reach the bridge.
A factory 2020 F-150 4x4 is 6'5" from the factory[1]
So I think you have you underestimation of the size of a truck. A common Lift would be 4in, and can go to 8in.
Your attempting to paint a picture of a "redneck" truck would be be a fully lifted, when lifting the truck you would then also add larger tires that would further lift the truck
So a Fully Lifted F-150 "Redneck" truck could be closer to 7'6" to 8' if not taller
[1]https://media.ford.com/content/dam/fordmedia/North%20America...