The energy cost of transport quantifies the energy efficiency of transporting an animal or vehicle from one place to another.
As a dimensionless quantity, it allows for the comparison of 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.
The metabolic cost of transport includes the basal metabolic cost of maintaining bodily function, and so goes to infinity as speed goes to zero.
[1] A human achieves the lowest cost of transport when walking at about 6 kilometres per hour (3.7 mph), at which speed a person of 70 kilograms (150 lb) has a metabolic rate of about 450 watts.
If only the additional metabolic cost (above the resting rate) is counted then the most efficient speed will be lower.
The optimal speed if both energy and distance traveled in a given time are taken into account (with some "price" for each) may be faster or slower than the speed giving the lowest COT.