It is not hard,there are even some manufacturers of assembled or kit models.

It is just most places such a craft would still require an appropriate license and requisite training to operate.

And in addition the frequent fatal crashes of military and civilian helicopters driven by experienced professionals using professionally serviced machines is an indication that the average civilian might not last long if automobile driving is any indication of vehicle control competence. If and when tight automatic computer control of civilian air traffic is ever attained there might be some possibilities.

Maybe someday someone will mass-produce a small cheap copter, but right now they're still too spendy for most people. Any flying machine is inherently more dangerous than a ground vehicle. Making them reasonably safe is expensive. You can't really make a helo as small as a car because the rotor needs to be large to be efficient. There are many small two-seat helos, but the rotors still require a lot of space. Also helos are not energy efficient. They suck up a lot of fuel, which is especially bad these days.

They exist, they just haven't 'caught-on'. When it's under 250lbs empty weight, it becomes an 'ultralight' and you no longer need a pilot's license to fly it, although I agree training is important. As for the 'highways' airplanes use, mostly the Victor-airways have been supplanted by direct-to GPS navigation--and if you're VFR, you don't even talk to a tower in many areas. See and avoid.

http://www.vortechonline.com/g1/

http://www.acecraftusa.com/

http://en.wikipedia.org/wiki/YH-32_Hornet

There was even a ducted-fan personal'jetpack' flyer at OshKosh this year. Again, an ultralight.

http://www.airventure.org/2008/news/080630_jetpack.html

As for a 'flying car' so many of the inventors have tried to design vertical take-off into them--I think this is not needed if you have a community 'landing street' --a wide boulevard or section of highway without obstructions.

For instance, the Moller 400--it's primarly a VTOL vehicle--which will slow it down as a plane and make it not useful at all on streets. It's just a funny looking bad helicopter.

Your idea highly depends on people being smart enough to realize when the day's winds might be too hazardous to traverse, and being diligent enough to heed those warnings and not test fate.

The usual cause of crashes is unexpected down drafts and machinery malfunctions. So just to address the malfunction possibility you want to have the least moving parts possible which means having an all electric helicopter, but only with a good enough energy storage technology. The only moving parts then would be the blades and the control system. And to address the bad weather cause of a crash you may have an airbag system or a parachute system that would sense that the craft was loosing altitude. But this could be the most eco-friendly vehicle from there being no need for roads.

Simple, safe, affordable:

Pick two.

The Bensen Gyrocopter came close to this. Out of production for decades, a few still flying.

There have been helicopter kits, such as the Scorpion and Scorpion Too. Not cheap or easy to build.