WHERE IS MY FLYING CAR? Every time a transportation technology lets us go further, faster, we use that technology to expand the radius of our lives. This is Marchetti's Constant. @tsungxu is building flying cars, because the time is right technologically and regulatorily, and because they can eliminate the speed-freedom trade-off that limits every transportation technology. This week's co-written essay explains why now is finally the time for flying cars, and what we can expect our world to…