Back to the futureThirty years ago, Marty McFly and Doc Brown got into a garage-modified DeLorean, activated the flux capacitor, and took off for…well, this year, to try and save Marty’s son from himself. Back to the Future played on a long-standing wish: flying cars.

As 2015 winds down, it’s easy to wonder why we don’t have flying cars. The easy answer is that the FAA would make such a dream a bureaucratic nightmare. That’s undoubtedly true, and if you throw in the Federal Highway Administration, you can see how such a great idea would be dead on arrival. But let’s take those two entities out of the equation.

Driving is two-dimensional. You move forward, backward, left, and right. Driving is also pretty easy. It’s not totally skillless or brainless, but we’ve done everything we can to make it so. Still, tens of thousands of people die every year on the highways in spite of some pretty impressive safety mechanisms and rules. Seatbelts are required (and their use is enforced, which wasn’t always the case); cars have roll cages, air bags, anti-lock brakes, and more. Still, no matter how idiot-proof we make a car, we manage to find ways to crash.

Flying, on the other hand, is three-dimensional, and that transition to and from the ground is, statistically, the most dangerous part of the flight. In the air, we have to deal with turbulence, even close to the ground. Imagine semis trying to fly next to a Camry. Unlike the DeLorean, we need to accept that a flying car will have wings, and those wings will be sized based on the payload. Semis and Camrys would be at constant risk of hitting each other because of the necessarily long wings on the semi, not to mention the wake turbulence. If you think on- and off-ramps are crowded now, imagine what it would be like trying to merge such disparately sized vehicles on and off the ground.

Infrastructure would be an issue as well, as we’d have to have much longer merge lanes to allow vehicles to get up to rotation speed. Consider that highways are designed to try to contain certain elements of a high-speed wreck (even if the only design element for this is building it in an isolated area). With skyways, we’d have to take into account that an in-flight collision would spread debris over a much larger area—which would necessitate additional safety enhancements for the drivers not only traveling quickly but now also falling to the ground. Buildings would need to be built to account for potential falling debris on the roof or through the windows.

In the end, flying cars just aren’t practical. In fact, if the skyways got too crowded, you’d be better back on the road, which is right where we are now. As fun as it is to daydream about defying gravity in every aspect of our lives, the truth is that without a quantum leap in strong, lightweight materials and powerful engines, it’s just not the way. But if you stick with flying airplanes, then where you’re going, you still don’t need roads.—Chip Wright