Google called competitors and government agencies to its own conference in June to share its vision of air-traffic control. The foundation of any system must be the ability to trust that all participants will reliably identify themselves and their locations, Vos said. The airspace must be open to any drones willing to follow the rules.

Networks of computers on the ground and in the air will set routes that avoid mid-air collisions. Humans will still be in charge, but unlike the current air-traffic system, controllers must rely on computers to make the split-second decisions necessary to keep drone traffic flowing and safe, he said.

Vos envisions a decentralized system with multiple private operators, most likely overseen by the Federal Aviation Administration.

Amazon has been tight-lipped about what it wants in a drone air-traffic system. Gur Kimchi, vice-president of the company's drone delivery division, Amazon Prime Air, issued a statement saying everyone in the industry "must work together."

PrecisionHawk, a Raleigh, N.C., drone company with about 100 employees, began developing its own drone traffic control system because the large agriculture and oil companies it flies for wanted something to keep tabs on unmanned flights. "Our clients need it," said Tyler Collins, the program's director.

In a recent demonstration over a North Carolina cattle farm, Collins and his team intentionally steered a quad-copter drone toward an imagined crop duster at work on an adjacent farm, the kind of hazardous scenario PrecisionHawk employees have seen in the real world.

Within seconds an alert popped up on the operator's smartwatch: "WARNING, nearing no-fly zone." When the operator ignored the warning, an autopilot took over and flew the whirring machine back to safety.

PrecisionHawk's system can automatically block its drones from flying into danger, such as around airports and other aircraft. And it makes a drone's real-time flight track available so others can stay away.

Skydio Inc., a Menlo Park, Calif., company founded a year ago, is developing arrays of tiny cameras mounted on drones and linked to computer chips that automatically guide them around trees, power lines and other obstructions, CEO Adam Bry said. San Francisco-based Airware and DroneDeploy are creating computer networks capable of showing where drones are operating.

After NASA put out word last year that it wanted help on its small-drone control system, 126 companies expressed interest, said NASA's Parimal Kopardekar, the project manager.

Kopardekar envisions a tiered system of tighter and tighter controls as drone traffic ramps up. If a drone pilot wants to fly over a remote farm, all he or she might need to do is file a notice to a centralized computer system. As unmanned flights become denser, the cloud-based system would need to track drones to ensure they wouldn't collide, just as radar follows traditional aircraft now, he said.

He's also contemplating drone-detection systems to ensure that stealth unmanned aircraft (such as the one that landed on the White House lawn Jan. 26) can be tracked. Kopardekar envisions turning over the design to the Federal Aviation Administration.

Bloomberg