Typically this is the measurement from the tractor front bumper to the rear trailer if a.
Double drop deck loads.
Double drop deck is a longer piece of a trailer called a well in the middle that dips below trailer axles.
The well ranges from 25 to 29 feet making it ideal for taller shorter freight.
Overhang the excavator arm extends over the ground allowing for the possibility for the arm to overhang the upper front or rear deck of the double drop.