Autonomous wheeled delivery would seem to accomplish Amazon's goals with the benefit of reduced cost per lb-mile. Vertical thrust air transport is very ineffic

Autonomous wheeled delivery would seem to accomplish Amazon's goals with the benefit of reduced cost per lb-mile. Vertical thrust air transport is very inefficient compared to ground transport - more energy is spent maintaining altitude than moving forward. Autonomous ground delivery does suffer from reduced navigational flexibility (anything other than curbside delivery is tricky). But it potentially has lower operating costs and safer failure modes. It may also be easier to integrate into existing regulatory frameworks.