If you have ever got unhappy at your petrol bill and dreamed of a car that runs on fresh air, your wishes are about to be answered.

French car giant PSA Peugeot Citroen believes it can put an air-powered car on the road by 2016. Its scientists say it will knock 45 per cent of fuel bills for an average driver. And when driving in towns and cities costs could be reduced by as much as 80 per cent because the car will be running on air for four-fifths of the time.

Air power would be used for city use, running below 43 miles an hour and available for 60 to 80 per cent of the time in city driving. By 2020, the car could be achieving an average of 117 miles a gallon, the company predicts.

For more than two years, 100 top scientists and engineers have been working on the air-powered car in top-secret conditions at Peugeot’s research and development center at Velizy, just south of Paris.

The engine system will be able to be fixed on any normal family car without changing its shape or size or reducing the boot size, provided the spare wheel is not stored there. From the outside, an air-powered car will look similar to an ordinary car. A spokesman said, “we are not talking about strange machines. These are going to be in everyday cars.”

The company said that as well as being more innocuous and cheaper to run，the air system created no extra dangers in an accident.

Drivers never run the risk of running out of compressed air late at night on a country road because the car will be fitted with an artificial brain.

The dream of the flying car could come down to earth soon as several start-ups like Chinese EHANG and Uber are developing so-called “passenger drones(无人机)”—self-flying drones big enough to ferry individual commuters around town—which could shrink commute(上下班往返) times from hours to minutes.

At first glance, human-carrying drones sound no more realistic than flying cars. Until recently inventors had never been able to marry automobiles and aircraft in a practical way. Yet a few companies have kept at it: Woburn, for example, has since 2006 been developing Transition, a “roadable aircraft” that resembles a small airplane that can fold its wings and drive on roads. A personal flying car in every garage has proved to be a tough sell, however, as there are serious safety concerns about asking the average commuter to train for a pilot’s license and take to the skies.

Passenger drones, by contrast, would operate autonomously and leave the “roadable” part behind in favor of larger versions of aircraft that already exist. Passenger drone designs favor “distributed electric propulsion(推进),” meaning instead of one large rotor powered by a large engine they have multiple propellers each powered by its own, smaller motor. This sacrifices lifting power and flight performance in exchange for mechanical simplicity and lighter weight—factors that could make them cheaper to operate. Quieter electric power would make the noise tolerable to city residents, although it remains to be seen how much weight such a vehicle could lift, and for how long.

With any of these vehicles, safety is the biggest concern and extends to both the aircraft and the automated systems flying them. Advanced artificial intelligence is needed to fly large numbers of autonomous aircraft without crashing them into one another or, say, the local news channel’s traffic helicopter. Carrying people from points A to B seems simple enough, but even the best AI struggles with surprises: What, for example, would a drone do if a landing area suddenly became unavailable? asks Sanjiv Singh, a Carnegie Mellon University robotics researcher. Instead of leaping to fully automated passenger drones, he suggests first testing the necessary AI in unmanned cargo(货物)runs, and adopting a “mixed mode” approach in early passenger services where pilots are assisted by AI co-pilots.

Technical challenges aside, start-ups promoting the technology will have to find a way to convince the public to give their drones a whirl, something that requires a much bigger leap of faith than getting into the backseat of a self-driving car. Passenger drone makers are “obviously still in the incubation(孵化) stages of technology development and improving the basics,” says Mike Hirschberg, executive director of the American Helicopter Society International. “But 20 or 30 years from now life may be a little like The Jetsons where you take advantage of the third dimension and have much more mobility, especially in urban close quarters where ground transportation is gridlocked.”

The passenger drone progress may follow a sloping takeoff rather than vertical leap. Carnegie Mellon’s Singh sees a long road ahead filled with lots of testing, analysis, regulation and efforts to win the public’s trust before the technology becomes a viable transportation option. “There is the danger of someone moving too fast and then having a problem that sets the industry back for some time,” he says.

Once a piece of fruit or a vegetable is picked, it starts to go bad. One common way to slow or stop that is to remove water from the foods. The process—dehydration (脱水)—typically uses heat, which can destroy their nutrients (营养). Now, researchers have come up with a new way, and it may help make dried fruit and vegetables more nutritious.

A common way to dry fruit and vegetables is to blow hot air across them. “But there’s another way to get air moving, and it doesn’t need a fan or heat,” says Kamran Iranshahi. He’s a mechanical engineer. Called “ionic wind (离子风)”, this technique had never seemed ready for being used widely. So Iranshahi’s team began improving the process.

In earlier research, the fruit and vegetables to be dried rested on a metal plate. As airflow never reached the underside of the foods, those pieces dried rather slowly. Iranshahi’s team has just replaced the plate with a metal mesh (网孔). That seemingly small change appears to have made a big difference. Using it, the team has not only cut the drying time, but in the latest test it also has dropped the energy use by more than 85 percent!

“People considered the hot air drying process as good enough for many years. But now, more and more people are worried about the health of their foods, so the popularity of drying foods with air moved by a fan or heat has waned,” says Vijaya Raghavan. He’s a mechanical engineer at McGill University in Montreal, Canada. “This team’s impressive invention”, he says, “may now make it easier to offer healthy and tasty dried foods.”

The new version of ionic wind could be more energy efficient, Iranshahi says. So far, few studies have tested the nutrient content of produce dried with ionic wind. However, Iranshahi notes, the new technique should destroy fewer nutrients than heat-based methods, and his team will focus on that in future studies.