If you listen to some entrepreneurs and investors, the flying car ? a longstanding staple of science fiction ? is right around the corner. Working prototypes exist. At least two companies already take orders for the vehicles, with deliveries promised next year.

The last decade has seen the introduction of practical consumer videoconferencing, voice recognition, drones, self-driving cars and many other items that once were found only in science fiction stories. It therefore might seem plausible that practical flying cars are around the corner. They aren’t. Indeed, massive safety, infrastructure and technology problems make them a near impossibility.

The first concern is safety. While flying a commercial airline is always safer than driving oneself the same distance, it’s an entirely different story if one looks at per-trip fatality rates. The Department of Transportation estimates that Americans take about 350 billion car trips per-year and experience about 30,000 fatal accidents; roughly one fatal accident per 11 million trips. By contrast, there are roughly 35 million scheduled air flights around the world each year. Over the past decade, the number of commercial aviation incidents that have proved fatal has averaged 17 annually. This means about one of every 2 million commercial air flights ends in death.

We see these fatalities every year, despite pilots’ years of intense training, planes’ extensive safety equipment requirements, regular maintenance checks and airlines’ need to maintain sterling reputations for safety. All of these provide far more safeguards than anything that applies to cars on the road.

It’s true that there are some factors that might make flying cars safer than commercial jetliners. They would travel at lower speeds and lower altitudes, for instance. But there’s no practical way to subject them to the same safety and training standards imposed on commercial airplanes if they are to become anything like a consumer product. Indeed, the per-trip fatality rates for private planes already is very likely higher than commercial airliners, but there are no worldwide statistics available. Safety advocates would make a plausible case for banning flying cars on these grounds alone.

Even if one thinks these risks are acceptable?and they probably are, given the potential advantages of flying cars?that doesn’t solve the even greater infrastructure or technological problems. The current working models of flying cars need runways to take off and land. Bringing them into regular use would require runways just about everywhere, without obviating the need for parking lots. The world’s busiest airport, Atlanta’s Hartsfield-Jackson, accommodates slightly less than 2,500 aircraft movements each day on its five runways and 4,700 acres. Any sizable office building would need its own version of Hartsfield-Jackson if people were to commute to work via their flying cars. The space to build facilities this size for flying cars simply doesn’t exist anywhere near any city of any size.

New technologies could theoretically obviate the need for runways. One Japanese team has shown off a modified lightweight drone supposedly capable of vertical takeoff and landing like a helicopter. But making these vehicles practical would require breakthroughs that appear to be decades away. Existing helicopters and military “jump jets” still require a significant amount of space to land, are even noisier than commercial jets and drink huge amounts of fuel. As such, they’re not really used for travel. Commercially produced helicopters have existed since the 1940s and aren’t currently used for scheduled commercial service anywhere in the United States. Technological breakthroughs could eventually solve these problems, but it’s unlikely that a few years of flying-car development will overcome problems that have bedeviled helicopter designers for more than seven decades.

While the promised 2017 deliveries of working flying cars seem unlikely, it’s far from impossible that a commercially produced civilian airplane with the kinds of retractable wings and safety equipment that would allow it to be driven on highways might make it to market within the next decade. But widely available flying cars, more likely than not, will remain clearly in the realm of science fiction.