There is need to overcome the fear of gravity while visualizing flying cars, persistent imagination and craving as intense as that which has created  mobile phones. 
Some visualizations can include imagining reaching a destination on time instead of remaining frustrated in a traffic jam, work being done in time with greater ease and efficiency as travel tension is reduced, feeling powerful while flying a  car in space with safety measures intact, travelling in free space instead of on congested roads, having the independence to think alone instead of being mobbed by thoughts from several around etc.
 If several start imagining & desiring flying in cars instead of driving slowly on roads, flying cars are likely to become a REALITY in the next 100 years.
Safety measures will come into place as the invention manifests but till there is collective  imaginations of individual cars  flying safely, the invention cannot take off smoothly.