A team of researchers at Carnegie Mellon University has found that drones carrying parcels use much less energy per parcel than diesel delivery trucks. In their paper published in the journal Patterns, the group described their tests of drones carrying packages and how they compared with trucks.

In this new effort, the researchers looked at the delivery of single small packages to a single destination—such as a customer’s home…

In so doing, they found that for single delivery of a package, drone delivery has a much smaller carbon footprint. More specifically, they found that a drone delivery accounted for 84% less greenhouse gas emissions than a diesel truck—it also used 94% less energy.

The researchers note that carbon savings depended very much on where in the country the electricity used to charge the drone batteries was produced.