People who drive on the Dan Ryan expressway in Chicago, one of the busiest roads in the world, often wish they could press a button and hover above all the congestion. Motorists have fantasized about flying cars for many years. In fact, the concept of "roadable aircraft" has existed since at least 1918, when a U.S. patent was issued for a vehicle capable of both driving on surface roads and flying through the air.

Numerous designs appeared in the 1940s and 1950s. A few concepts even got off the ground, such as the 1937 Aerobile, the 1947 Airphibian and the 1956 Aerocar. In recent years, visionaries such as Paul Moller have kept the dream alive. Moller has been working on a personal vertical takeoff and landing vehicle for more than 40 years. His four-person fan-powered Skycar is currently undergoing initial flight-testing in California.

With almost 1 billion automobiles clogging roads around the world, interest in flying cars is heating up. While most schemes involve tinkerers working in small garages, some of the biggest names in the aerospace industry are exploring the concept. For instance, engineers at the Phantom Works of Boeing Co. (Chicago) have been studying how to make a flying car that costs the same as a luxury vehicle and is easy and safe to fly. They're also focusing on new air traffic management systems that would create "highways in the sky."

At the recent Experimental Aircraft Association AirVenture fly-in show in Oshkosh, WI, one of the latest flying car concepts was on public display for the first time. The Transition is a personal air vehicle (PAV) "designed to make general aviation more practical for personal transportation," says Anna Mracek, chief operating officer of Terrafugia Inc. (Cambridge, MA). Mracek claims that the 1,320-pound vehicle will be able to drive at normal highway speed, fly at speeds similar to a light sport aircraft and park in a standard garage.

The Transition is the brainchild of Carl Dietrich, cofounder and CEO of Terrafugia, and a graduate student at the Massachusetts Institute of Technology (MIT, Cambridge, MA). Dietrich recently received the Lemelson-MIT Student Prize for being the most innovative student at MIT in the past year. Dietrich and several of his colleagues at MIT's Department of Aeronautics and Astronautics founded Terrafugia, which is derived from the Latin for "escape from land."

The Transition, which is set to debut in 2010, features a folding wing mechanism. The 19-foot-long vehicle will have a 27-foot wingspan, but it will be less than 7 feet wide when the wings are folded up. Unlike the Skycar and other concepts, the Transition will not be able to make vertical takeoffs. Indeed, it will require a runway that's at least 1,500 feet long.

"It will be the first PAV that can transition from air mode to land mode via an automatic control system and fit in the garage space of a standard SUV," says Mracek. "This makes the switch from home to freeway to airport and back seamless and easy for any pilot. The Transition will also be the most economical form of travel between 100 and 500 miles for people who value their time, beating out conventional regional airlines and automobile road trips."

According to Dietrich, the ability to transition from air to land modes also removes the worry of having to cancel a trip due to bad weather. With the Transition, pilots who encounter inclement weather or marginal visibilities and ceilings will be able to land at a nearby airport and continue their trip on the road. "The Transition will allow people to expand their weekend trip options, make trips they otherwise wouldn't, and do it safely and affordably," explains Dietrich.

The Transition will fall under the Federal Aviation Administration's Light Sport category, making it both easier and safer to fly. Transition owners will need a Sport Pilot's license, which can be obtained in roughly half the time as a traditional private pilot certificate.

Terrafugia engineers recently conducted a series of wind tunnel tests using a 1/5th scale model. They're now focusing on the folding and locking mechanism for the wings, guided by senior design engineer Milo Mracek. He developed the multiple fold wing mechanisms currently used on many military missiles. In fact, several of the lessons learned from those projects are being applied to the Transition.

The engineers recently conducted a preliminary design review of the wing folding mechanism. "This review was a critical step in mitigating the concerns expressed by members of the pilot community surrounding automatic folding wings on a general aviation aircraft," says Dietrich. "The preliminary design of the folding and locking mechanism is moving forward to the detailed, piece-part design stage.

"Once the designs of all the specific parts have been isolated and analyzed using finite element analysis techniques, key areas for weight reduction will be identified and the design will move on to the critical review stage and manufacturing analyses," adds Dietrich. "Various components of the folding mechanism, which features a single actuator drive for each wing and locking pins that will be visible to the pilot during preflight checks, will now move into the prototyping stage."

By using advanced engineering, Dietrich hopes to succeed where others have failed. "There is a perceived need for a vehicle of this type," he explains. "Unfortunately, the cost-benefit of [earlier flying car concepts] never justified serious financial backing. The real need was not sufficiently acute to justify the performance sacrifices of a dual-use vehicle.

"Consequently, the flying car was relegated to the realm of lone inventors or visionaries that had the desire, but not the resources or capability to build a practical, commercially viable entity," concludes Dietrich. "Terrafugia is the company that will change this paradigm and be the first to successfully bring a roadable personal air vehicle to the general aviation marketplace."