Reno (US): NASA has launched the final stage of a four-year effort to develop a national traffic management system for drones, testing them in cities for the first time beyond the operator’s line of sight as businesses look in the future to unleash the unmanned devices in droves above busy streets and buildings. Multiple drones took to the air at the same time above downtown Reno this week in a series of simulations testing emerging technology that someday will be used to manage hundreds of thousands of small unmanned commercial aircraft delivering packages, pizzas and medical supplies. Also Read – ‘Hong Kong won’t rule out Chinese help over protests'”This activity is the latest and most technical challenge we have done with unmanned aerial systems,” said David Korsmeyer, associate director of research and technology at NASA’s Ames Research Center in Mountain View, California. An autonomous drone took off Tuesday from the rooftop of a five-story casino parking garage and landed on the roof of another out of view across the street. It hovered as onboard sensors adjusted for gusty winds before returning close to the center of the launchpad. Also Read – Pak Army chief accompanies Imran at key meetings in ChinaEquipped with GPS, others flew at each other no higher than city streetlights but were able to avoid colliding through onboard tracking systems connected to NASA’s computers on the ground. Similar tests have been conducted in remote and rural areas. The Federal Aviation Administration has authorized individual test flights in cities before but never for multiple drones or outside the sight of the operator. The new round of tests continuing this summer in Reno and Corpus Christi, Texas, marks the first time simulations have combined all those scenarios, said Chris Walach, executive director of the Nevada Institute of Autonomous Systems, which is running the Reno tests of unmanned aerial vehicles, or UAVs.