D-value (transport)

In transport, D-value is a rating in kN that is typically attributed to mechanical couplings, and reflects dynamic loading limits between a towing vehicle and a trailer.
The corresponding formula for a truck and trailer combination, used to determine the required D-value of a coupling, is:
T = Weight of towing vehicle including the vertical load on the fifth wheel

R = Total weight of the loaded semi-trailer

U = Vertical load on the fifth wheel

g = Acceleration due to gravity
D = g x /)