I think truck drivers are more or less trained to ignore everything but the last-resort sign. Near where I live, there's a small bridge (railroad on top, road c

I think truck drivers are more or less trained to ignore everything but the last-resort sign. Near where I live, there's a small bridge (railroad on top, road crosses below) with not enough height. It has some limit on vehicle height that is posted on the streets quite some distance away, so that drivers can choose an alternative route. Of course the bridges always will be higher than the posted limit, taking account inaccuracies of the actual vehicle height and movement during driving, so drivers take a certain amount of leeway for granted. Now I've seen them back out after having touched the posted bar in front of the bridge and having (almost or actually) touched the structure countless times. Probably with the consecutively more noticable signs in the video, it's made such that the later signs trigger just at slightly bigger heights than the earlier ones, to avoid scaring drivers that made it through the earlier ones un-warned. So I can see that a driver would try testing the later ones, just because he's pretty sure that he might fit, eventually.