Dump Truck Crashes Into Highway Sign [VIDEO]

A dump truck driver was not aware that the bed of his truck was up and when he came up on road sign over a highway he was quickly reminded of his error. 

How did this driver NOT KNOW that the bed of the truck was in the upright position? I never drove one of these trucks, but wouldn't at least feel a difference in how the truck is driving?

In any case, the driver took down the sign and probably had a lot of explaining to do to his boss and police. Ouch.