Why your pizza may never be delivered by drone

For years tech companies such as Amazon, Alphabet and Uber have promised us delivery drones bringing goods to our doorsteps in a matter of minutes. So why are they taking so long to arrive? If our skies are to become as crowded as our streets, airspace rules need updating to prevent accidents, terrorist attacks, and related problems, such as noise pollution. But that's easier said than done. According to a recent study by Nasa, the noise made by road traffic was "systematically judged to be less annoying" than the high-pitched buzzing made by drones.