Imagine a city where there are no roads. Imagine a city where paradise has not been paved, and turned into a parking lot. Imagine a city where asphalt and concrete are nowhere to be seen. Instead, the areas between buildings and houses are filled with grassy lawns, gardens and parks. That image alone should make the prospect of a world without ground-based vehicles immensely attractive.

Many questions spring to mind, of course. Not being a scientist, I won't pretend to answer them "scientifically". My goal in this column is to paint a picture of what we should have, and hopefully one day, will have, in terms of transportation. To the naysayers, I say, phooey! Which medieval person could imagine that we would be building a space station in the year 2006? Flight itself was thought impossible throughout most of human history. Yet, here we are, with "personal flying vehicles" already in production at a number of companies, including the Moller "Sky Car" at http://moller.com and the "AirScooter" at http://airscooter.com.

When I think of flying vehicles, I immediately think of a number of major requirements. Priority Number One for me is easy to explain: the vehicle should not be able to fall out of the sky and go boom. A simple need, based on common sense. When the vehicle's propulsion system stops, the vehicle should continue to float, to ensure the safety of all concerned. And yes... it's a tall order.

Because of the above priority, I propose that the current method of flight, based on wings and the requirement of forward movement to stay in the air, be replaced with "gravity conversion". Gravity is powerful enough to bring an airplane down, so let's learn to convert it to keep a vehicle afloat. By using powerful batteries as a backup system, a vehicle would not require a working engine to stay in the air. Gravity conversion may seem impossible now, but to a forward thinking scientist, it's just one more challenge to overcome.

I believe that the same system of gravity conversion could power vehicle movement. Whatever propulsion method is used, however, it should be completely clean and silent. Just imagine how horrible it would be if all the birds of the air emitted exhaust, and sounded like Jet Skis. As it is, we can sit and watch hundreds of birds wheel across the landscape without any significant noise or pollution. There are occasional bird droppings, I admit.

The next major issue for flying vehicles is a rock-solid, automated guidance system. One only has to imagine rush hour in any major city to realize that having crowded vehicles in three dimensions could be disastrous. One might think that three dimensional "roads" are the answer, but I believe that the answer lies in nature, once again with birds.

When you have thousands of birds in the air, why don't they crash into each other? They do crash into windshields of cars, or windows of houses, sometimes, but I think that it's because they're not really programmed to deal with windows. With computers becoming truly powerful, let's outfit our personal flying vehicles with sensors that face in all directions and then program the vehicles to automatically respond when other vehicles come too close. By using the multidimensional guidance systems of birds, I believe that we could eliminate the need for "roads through the air".

What about parking lots? One must be able to fly to the mall; so where to put one's flying vehicle? The answer is "in the air." The vehicles would use vertical structures that are in essence parking garages, but in real terms quite different from today's asphalt, driveway type garages. The design could be like a beehive, or it could be a treelike structure, with hundreds of branches sprouting out from a trunk, with each branch having many vehicle slots. When people disembarked from the vehicle, they could travel via fast pneumatic tubes and elevators down to the ground, or into the structure itself. Parking slots or decks could even be built into office structures, allowing people to fly directly to the 81st floor and get out at their office.

With personal flying vehicles, vehicle speed could dramatically increase. Travel time would be cut down, allowing people to visit their friends and family far more often. With vehicles that fulfilled the above requirements, the quality of life for everyone in society would dramatically improve. The world would become green again, and the global parking lot might once again resemble paradise.

[Note: I have written a second column, as a follow up to this one, called "Dark Energy", A Clean Sky and Personal Flying Vehicles.]