Modelling suggests that within a year or so there will be about 400,000 commercial drones operating in the US, alongside at least two million others used only for recreational purposes.
The potential for airborne collisions is thus all too easy to imagine.
The good folk at NASA imagined it quite a while ago and since 2015 has been field testing the technical and navigational challenges of operating drones in crowded skies. The organisation is running a program called the Unmanned Aircraft Systems Management project (UTM).
From now until August, the project kicks over into its most challenging phases, investigating the difficulties of using drones to navigate city streets. Trials of its newly developed traffic management software are underway in Reno, in Nevada, and Corpus Christi, Texas.