Flying cars may be 25 years or more away 。Next generation small aircraft may look like this Farnborough F1 concept。

As motorways² become more and more clogged³ up with traffic, a new generation of flying cars will be needed to ferry people along skyways.

That is the verdict of engineers from the US space agency and aeronautical⁴ firms, who envision future commuters travelling by "skycar".

These could look much like the concept skycar shown in the picture, designed by Boeing research and development.

However, such vehicles could be some 25 years from appearing on the market.

Efforts to build flying vehicles in the past have not been very successful.

Such vehicles would not only be expensive and require the skills of a trained pilot to fly, but there are significant engineering challenges involved in developing them.

"When you try to combine them you get the worst of both worlds: a very heavy, slow, expensive vehicle that's hard to use," said Mark Moore, head of the personal air vehicle (PAV) division of the vehicle systems program at Nasa's Langley Research Center in Hampton, US.

But Boeing is also considering how to police the airways⁵ - and prevent total pandemonium⁶ - if thousands of flying cars enter the skies.

"The neat, gee-whiz part is thinking about what would the vehicle itself look like," said Dick Paul, a vice⁷ president with Phantom⁸ Works, Boeing's research and development arm.

"But we're trying to think through all the ramifications⁹ of what would it take to deploy¹⁰ a fleet of these."

Past proposals to solve this problem have included artificial intelligence systems to prevent collisions between air traffic.

Nasa is working on flying vehicles with the initial goal of transforming small plane travel.

Small planes are generally costly¹¹, loud, require months of training and lots of money to operate, making flying to work impractical¹² for most people.

But within five years, Nasa researchers hope to develop technology for a small plane that can fly out of regional airports, costs less than $100,000 (￡55,725), is as quiet as a motorcycle and as simple to operate as a car.

Although it would not have any road-driving capabilities¹³, it would bring this form of travel within the grasp of a wider section of people. Technology would automate¹⁴ many of the pilot's functions.

This Small Aircraft Transportation System (Sats) would divert pressure away from the "hub-and-spoke¹⁵" model of air travel.

Hub-and-spoke refers to the typically US model of passengers being processed through large "hub" airports and then on to secondary flights to "spoke" airports near their final destination.