A system's environmental footprint can be thought of as having two components – a fixed component that has impacts that are mostly or wholly independent of the volume of economic activity associated with the system, and a variable component that is roughly proportional to the amount of economic activity. Prior research has also described supply chain emissions by classifying them in stationary and non-stationary sources. In The case of a supply chain, the emissions associated with managing logistics facilities represent the fixed component of the logistics footprint while the operation of transport vehicles generate emissions that scale linearly with total transport distances. As macro-level data shows and other life cycle assessment studies confirm, impacts associated with transportation are significantly greater than those associated with facilities when impacts are allocated to individual products and their life cycles.