I've seen plenty of low bridges. There are two in my hometown in Indiana, but both are clearly marked. While a bunch of folks have hit them and others I've seen over the years, I still maintain you have to be RV challenged to do so. I once saw a rig stuck under a bridge on US 41 in Chattanooga and then there was the time that some guy drove under a low overhead at the Flying J in I believe Eureka, CA or somewhere up there. If I remember, that one was discussed here on the BB. Still, it was his fault as are all of them. Situational awareness should be a prerequisite for driving an RV. (like the time I scraped my batwing antenna off on a tree limb on a class C I owned) my fault, didn't do my last walk around and left the antenna up. Entirely my fault.
Most if not all of the dings we see in bridges are from folks carrying backhoes or other too tall devices and not paying attention. There are zero RVs made that exceed the Federal Height Limit and if you are driving or pulling an RV that is close, then you ought to be vigilant and pay attention to low bridge warnings. If for some unknown reason, you miss the warning, common sense should tell you not to drive or pull a 12 foot tall rig under an 11 foot clearance opening.
I've gone through the tunnel on the east side of Zion NP twice in my pusher. Believe me, I adhere to the rule about driving right down the center line of the road because the sides are obviously too low for me.
However, I've never seen one too low on an Interstate and have never felt the need to buy software to let me know when or where they were.