# Cost of transport

The energy cost of transport quantifies the energy efficiency transporting an animal or vehicle from one place to another. It allows for the comparison dissimilar animals or modes of transportation. It has a wide range of applications, from comparing human gaits to observing the change in efficiency of trains over time.

It is calculated in one of two ways, both shown in the following definition:

where ${\displaystyle W}$ is the energy input to the system, which has mass ${\displaystyle m}$, that is used to move the system a distance ${\displaystyle d}$, and ${\displaystyle g}$ is Standard gravity. Alternatively, one can use the power input to the system ${\displaystyle P}$ used to move the system at a constant velocity ${\displaystyle v}$. The cost of transport is non-dimensional.

It is also called specific tractive force or specific resistance (see von Kármán–Gabrielli diagram), or the energy index.[1] When the energy comes from metabolic processes (i.e., for animals), it is often called the metabolic cost of transport.

The metabolic cost of transport for human walking is about 0.1.[2]