We know that much of a delivery network's cost is the last mile, but I'd be interested in the costs of the last 100 yards. Suddenly, instead of one driver/one truck per neighborhood per day it's one stop per neighborhood per day. They can stop once or twice in the neighborhood, load drones with packages and then drones do all the deliveries. If you even have a separate "loader" in the back, you can have the driver jump out and make the few targeted heavy package (20+lbs) deliveries.