Class A Low Bridge Accident

I do wonder if putting a sign ON the low bridge/overpass/tunnel is enough. I've been on some roads where it is impossible to pull over or turn around or exit within visual distance of the potential hazard. What do you do?

I've seen signs that indicate "last exit before bridge". Should there be signs that say "vehicles over 9' 8" exit now" so the driver can avoid the hazard. Especially in heavy traffic, you could find yourself "pushed" forward.