Angle of departure
The angle of departure of any vehicle is the angle between the ground and a line running from a rear tire to the lowest-hanging component directly behind it, usually the rear bumper. In Seattle, where I live, or in places like San Francisco, there are topography challenges from an overabundance of hills we must navigate with the tractor drawn aerial apparatus. Because of the length of a tractor drawn aerial and the steepness of some hills the angle of departure must be a consideration.
Manufacturers can account for the angle of departure by simply notching out the back bottom part of the trailer. This provides more space between the bottom of the trailer and the ground, reducing the likelihood of the trailer hitting the ground as it drives up a steep hill. (Click to enlarge)
Of course making a turn up a steep hill can also reduce the angle of departure even more.