Runs on electricity or other low/zero emission fuel source
Lasts an appreciable amount of time before recharge
Then it may free up public roads enough to push pedestrian and bike usage while offering people a large incentive to go electric. I just don't think the technology for personal automobile-aircraft hybrids is there yet.
Why make one more lane bro up in the sky when we can make trains? We already have the technology to solve traffic and it DOESN'T involve making more cars, flying or otherwise. All flying cars would do to traffic is jam it up at the places where you park, and also create traffic in unplanned places like people's attics and second floor apartments.