Skipping rush hour traffic by hopping into a flying taxi may seem like a long shot dreamt up by science fiction authors, but a number of corporations and startups are currently working on prototypes.

In October, Cora, one of the aforementioned companies and startups, partnered with Air New Zealand in a step towards commercialization. Boeing tested out their own self-flying taxis in January. Uber even has plans to launch a flying rideshare service by 2023!

These prototypes may be electric and give off no greenhouse gases, but mining and producing the electricity to charge their batteries still has an environmental cost to it. But the flying taxis of the future may be greener than they seem—provided everyone carpools and only uses them for long-distance travel. This comes from a study done by University of Michigan scientists, and published in Nature Communications last Tuesday, who recently considered the cost of the futuristic vehicles compared to ground-based cars.

"I was surprised by how competitive the flying cars were in these scenarios that we explored because of the energy intensity to lift the vehicle."

Study Author and Director of University of Michigan's Center for Sustainable Systems Gregory Keoleian

Flying cars rely on distributed electric propulsion. This is essentially a series of small propellers on the vehicle's wings. By using this, they can avoid runways, moving much more like a drone, with a vertical take-off and landing.

To understand the necessary energy, scientists used data from other scientific and industry reports. the model they considered had one pilot and four passenger seats, flew at an altitude of 1,000 feet, and could travel up to 150 miles per hour. This was compared to two cars: one gasoline-powered vehicle that gets 34.1 miles per gallon; the other an electric vehicle that, based on its energy use, got a whopping 108.5 miles per gallon! Efficiency was compared at distances anywhere from 3 all the way up to 155 miles.

For short trips of 22 miles or less, both of the cars beat the sky taxi in efficiency. Most of Americans only make short trips, the average distance being around 11 miles. This would leave the taxi mostly hovering, using up a lot of energy.

Over long distances, the taxi's efficiency improved. for a nonstop, 62-mile trip, use of the taxi led to 35 percent fewer greenhouse gas emissions than the gasoline car. Compared to the electric vehicle, unfortunately, the taxi had 28 percent more emissions. However, this scenario ignores passengers. If you load all four people into the taxi and compare it to cars with average occupancy, 1.54 people, to be exact, it looks even greener. On the basis of emissions produced per passenger across the same 62 miles, the taxi has 52 percent fewer emissions than the gasoline car and 6 percent less than the electric!
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This implies that these vehicles fill a very specific role: carpooling over long distances. They could also be useful in both congested areas and those without straight paths.

"If you're flying from Detroit to Cleveland, the air taxi can go right over the water. Whereas the ground-based vehicle has to go around Lake Erie."

Study Author and Director of University of Michigan's Center for Sustainable Systems Gregory Keoleian

They can also be used in commuter nightmares, such as Southern California. Driving from Irvine to Malibu during rush hour can take up to three-and-a-half hours! But, assuming air taxis don't grow so rapidly in popularity that they create their own traffic, flying can cut this trip down to a much more mangable 27 minutes.

"You save up to 80 percent of travel time flying versus going on the ground. It's a lot more pleasant to just cruise over at 1,000 feet and not be stuck behind big trucks on the highway."

Study's First Author and Sustainable Systems Graduate Student Akshat Kasliwal

It also pays off for air taxi companies to incentivise carpooling.

"It is very important that you have high-occupancy levels similar to how a commercial airline is operated—the more you can fill the seats, the more revenue and the higher your profitability."

Study Co-author and Business Sustainability Graduate Student Jim Gawron

The business model tends to favor the more sustainable carpool trips.

Researchers hope that tech companies use their framework to evaluate prototypes. Since some of these might take off as early as 2023, it is important to consider what their impact, positive or negative, might be. Keoleian hopes, from a sustainability standpoint, that this new service doesn't make it easier to live further away from work.

"We don't want air taxis to encourage something like sprawl."

Study Author and Director of University of Michigan's Center for Sustainable Systems Gregory Keoleian

There are also factors other than greenhouse gasses to consider.
While the study did compare energy-related emissions, from mining, production, transport, and using fuel, of the different vehicles, it didn't show the full picture. The environmental impacts of making and disposing the machinery were not included. The modeled aircraft was lighter than the typical sedan. Generally, while less materials means less environmental impact, the type of material also matters. Keoleian adds that carbon fiber, often used in light aircraft, is environmentally costly to produce.

Implementing safe travel regulations will also be a key in reducing this new technology's negative side effects.
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"If these are flying around like The Jetsons, that's a lot of visual pollution."

Study Author and Director of University of Michigan's Center for Sustainable Systems Gregory Keoleian

The team hopes that as companies like Uber Elevate move forward with design, they consider such impacts.

"It's really important for companies like that to understand the findings and recommendations of our studies."

Study Author and Director of University of Michigan's Center for Sustainable Systems Gregory Keoleian