See the new rules the White House released intended to keep drones from colliding with things in flight and people on the ground. (Jhaan Elker/The Washington Post)

The era when a glance toward the sky is more likely to reveal a small unmanned aircraft than an airplane or a bird seems remote to most people, but it drew closer Tuesday as the White House released regulations intended to keep drones from colliding with things in flight and people on the ground.

Many years in the making, and after 4,600 public comments, the new rules have a narrow focus that will be criticized by those who hoped the Federal Aviation Administration would sketch out a futuristic grand plan, while drawing praise from others who worried that the agency would offer too much regulation too soon.

“The mantra is flexibility when possible, and structure when absolutely necessary,” Parimal H. Kopardekar, a NASA researcher who is contributing to the design of a drone traffic management system, said in advance of Tuesday’s White House announcement.

Prior to the announcement of these new regulations, the guidelines provided by the federal government had focused primarily on the burgeoning hobby market rather than on the much more complex business of integrating the swarm of commercial drones expected in the skies in the next decade.

A hexacopter drone is flown during a drone demonstration in 2015. (Alex Brandon/AP)

They require that drone pilots keep their aircraft within sight, operate only in daylight, use drones weighing less than 55 pounds, fly no higher than 400 feet and not fly over strangers. Commercial operators will be vetted by the Transportation Security Administration and required to pass an aeronautical knowledge exam at an FAA-approved test center. The same security considerations that ban nongovernment airplanes from flying over the District of Columbia would apply to drones.

What the rules don’t address are the over-the-horizon drone operations desired by many commercial aspirants, a fact that FAA Administrator Michael P. Huerta acknowledged will have to be addressed in concert with the industry.

“The FAA’s role is to set a framework for safety without unduly impeding innovation,” he said in April. “We recognize that we cannot solve these types of challenges alone. We need the expertise and collaboration of key industry stakeholders.”

The time when drones will be more common than airplanes, and perhaps birds, over America’s cities is closer than people realize, experts say. Already, the number of registered drones exceeds the number of airplanes. With the myriad commercial uses for drones, the FAA, NASA and would-be fleet operators are hard at work on systems to keep them from crashing into one another.

Although a drone in flight now is as rare as Sputnik-era satellites were in the late 1950s, in a decade or so it’s unlikely anyone will bother to look up at one. The FAA estimates that drone sales will grow from 2.5 million this year to 7 million in 2020. The overwhelming majority of drones now registered with the FAA — about 99 percent — are owned by people who fly them as a hobby.

But there already are 10,602 registered commercial drones, and the potential for growth in their use is enormous. The FAA projects that sales of drones intended for commercial use will triple from 600,000 this year to 2.7 million in 2020.

“Drones are essentially aerial robots,” said Ed Felten, deputy chief technology officer in the White House Office of Science and Technology Policy. “These are much more than flying cameras. It’s still a nascent technology, and its potential uses and benefits are only starting to be understood.”

Drones will be used to monitor traffic, search for missing persons and crime suspects, help control the flow of movement at big construction and agricultural sites, maintain surveillance over closely guarded locations, collect video imagery at athletic events and during breaking news events and provide doorstep package delivery.

“What seems to be missing from the regulations is the issue of enforcement. Given the growing prevalence of drones, it is hard to see how the Federal Aviation Administration actually can ensure that these rules are followed,” said Sarah Kreps, a Cornell University law professor. “The new regulations also sidestep the more revolutionary commercial technology that is over-the-horizon of the type that Amazon would need to deliver packages. The FAA acknowledges that it punted on these issues for now, leaving it to industry to innovate anti-collision mechanisms. At which time the FAA will likely step in again with a new set of regulations.”

Huerta is aware that to keep pace with the commercial drone industry, his agency will have to overcome its legacy as a rigid bureaucracy that moves at glacial speed.

“We’re asking, ‘Are we fast enough? Are we flexible enough?’ ” he said at a conference of unmanned aircraft experts.

The rule allows drone operators to apply for a wide range of waivers, including for night flights and over-the-horizon commercial operations in which line-of-sight contact with a drone is not maintained.

“What the applicants will have to do is demonstrate how we can maintain safety,” Huerta said Tuesday., one company that plans to use drones for package delivery, says the management systems that will keep drones from colliding — with each other, with airplanes and with people — need to be conceived faster than the FAA norm.

“We simply don’t have the option of going through the traditional kind of five-year time span in which we come up with regulatory outcomes and the standards,” Sean Cassidy, director of strategic partnerships at Amazon Prime Air, said last week, prior to the announcement. “Actually, speed is our friend. [Unmanned traffic management (UTM)] is a powerful force to help introduce coherence where there is going to be increasing chaos.”

The FAA should set and enforce standards for commercial traffic, he said, but otherwise leave it to industry.

“They’re not going to be in the business of actually managing or helping to supply those essential services for traffic,” Cassidy said. “That is something that is absolutely best delegated to the industry and the innovators. Let them figure that solution out.”

(Amazon founder Jeffrey P. Bezos owns The Washington Post.)

Cassidy said operators of commercial fleets must come up with standard interfaces and protocols recognized by other drone fleets.

“Basically, controller-to-controller protocols,” he said.

MIT professor John Hansman agrees.

“It’s not going to be a ­command-and-control system because we can’t afford it and we don’t need it,” he said. “It really will be an information service and an information protocol. It’s really going to be an information exchange. The potential is that the UTM would become a common platform that people could sign on to.”

NASA’s Kopardekar points to a 1920s photo of a Los Angeles intersection that shows a chaotic melange of cars, horse carriages, trolley cars and pedestrians.

“This is what we’re trying to avoid, looking at the future, and saying what do I need to have in place so that we enable the 2.7 million commercial drones that are forecast by 2020?” he said.

Clarification: This story has been updated to clearly distinguish between guidelines for the hobby market and new regulations for commercial drones.