I already told you... And yes if your in an area where the height of a object is in question you would approach with caution.. There are plenty of pictures with truck out there that had the roofs peeled back because they didn't. A responsible driver would absolutely check.
To imply one would stop on a highway is pretty ignorant knowing that all major roadways have to meet certain bridge heights, not the case with secondary roads..
Like I said, the lights are designed to project light at a specific angle in front of the vehicle, seeing a faint glow reflected on the underside of a bridge (example) is ok, but if you see 5 distinct spots of light, you need to check.
THAT is why they are called clearance lights (I know its English) otherwise the would just be called MARKER lights...