We've been down this road/runway time and again and while it is possible, it's not going to be practical for a long time. From a licensed private pilot who also holds a class B CDL and could actually LEGALLY drive/fly this thing, here are the reasons why this ain't going to happen....
1. The Car/Plane will need to be certified by TWO authorities, the NHTSA and the FAA (in the USA).
2. It will have to meet the minimum crash standards of the NHTSA, the Emission standards for other vehicles including the OBDII and Cafe mileage standards, yet meet the FAA's technical standard for a commercially produced aircraft (assume you don't build these yourself..)
3. Designing for both authorities will make it a horrible car and a worse airplane. It won't be comfortable and it will be hugely expensive.
4. The driver/pilot will need to be licensed to drive as well as have a suitable pilot's license, ratings, medical certificate, log book endorsements, and be current for the type of flying to be done in order to take passengers. Flying is an expensive hobby and you have to fly regularly to be proficient and safe.
5. ALL maintenance will need to be done by properly certified (by the FAA) mechanics using fully vetted and certified parts, and you thought a brake job was expensive for your car, trust me, you haven't seen anything, and you simply won't be able to do ANY work yourself or buy tires from your local tire store because they won't be able to legally even loosen the lug nuts on your car/airplane thing.
6. Large Cities Usually sit under large areas of restricted airspace where flying these things would require a minimum set of navigational equipment, communications equipment and procedural methods to be followed. This is more than just going through the toll booth or HOV lanes. You will need to have a scheduled transit time and an approved filed flight plan in some cases and be talking to ATC in most cases.
7. VSTOL capable aircraft are usually not fuel efficient being heavy and complicated devices. They have limited useful load for the fuel they burn and suffer from being low range because you simply cannot lift fuel AND people, suitcases, groceries and the like. (The Harrier and V22 don't fix this issue..) You won't be go very far or fly very long.
8. Alcohol in motor fuels is going to be an issue for aircraft operating conditions.
It's simply not a practical idea. Sounds like it would be great, but it's just got some serious problems even before you get to thinking about the physics of the whole it's a car, it's a plane engineering problem.