It’s easy to take the speed of modern delivery for granted. You hop online, order whatever you need, click okay, and in two to five business days it’s arrived on your doorstep. But what we don’t see are the gallons of diesel fuel burning in the engines of delivery trucks perpetually crisscrossing communities to ensure that every consumer has gets their goods on time. Running these trucks on diesel fuel creates a significant amount of greenhouse gases (GHG) into the atmosphere.

But some companies are exploring ways to introduce autonomous aerial vehicles into their delivery fleets. Unlike diesel trucks, these drones run on batteries charged on electricity. But just how much of an effect can using drones have on energy use in the freight sector? Researchers from Lawrence Livermore National Laboratory, Carnegie Mellon University, SRI International, and University of Colorado Boulder set out to quantify just that.

“Truck transport is responsible for 24% of transportation-related greenhouse gas emissions,” the team explains, “and comprises 23% of transportation energy use in the USA. Hence, changes to the industry are important to the environment and the energy system.”

In a paper recently published in Nature Communications, titled “Energy use and life cycle greenhouse gas emissions of drones for commercial package delivery,” the team examined the full impact of drone introduction on the freight sector. While the drones themselves put out considerably fewer GHG emissions than diesel trucks, the team wanted to know the full impact of the system that makes both drone and diesel delivery possible.

For instance, drones are powered by electricity, and their emissions depend on the types of power plants in the region. The amount of fossil fuels used for electricity varies from region to region in the United States, so the team quantified the impacts of drone delivery in different areas of the country.

Fuel is only one of the considerations when measuring the life cycle impacts of drone delivery. The current practical range of drones used for freight delivery is approximately four kilometers, due to battery limitations. Because their range is so short, using drones for on-demand delivery would require a network of delivery warehouses, allowing for either frequent recharging or shorter delivery ranges.

“Although drones consume less energy per package-km than delivery trucks,” the team explains in the paper, “the additional warehouse energy required and the longer distances traveled by drones per package greatly increase the life cycle impacts.”