The problem with a flooded road is you cant tell if the road is still intact or has been eroded by current. A good rule of thumb is to keep the water line below the frame rails. As others have mentioned much deeper than that and you run the risk of water shorting out the electrical system AND getting into the vent tubes of the differentials. (the later is not an immediate danger to the vehicle but will cause some expensive repairs if not taken care of soon after a water crossing with any depth) Not to mention the buoyancy risk. I have tried crossing a body of water that was only hub high(half way up the tire) and because of the power of the current it began pushing my truck sideways. However slight it was it was still in fact moving the vehicle and I was nowhere near the frame rails in depth.water crossings if the bottom(solid or soft) and depth is unknown is a scary proposition.