For many people of a certain age, the idea of flying taxis, ferrying people around cities, brings to mind the once popular animated TV series The Jetsons.
The 1960s show depicted a family living in a futuristic metropolis where commuters headed to work in cars that soared through the air.
Two decades into the 21st Century, and the science fiction dreams of the creators of The Jetsons are closer than ever to becoming a reality.
With the likes of Uber and Boeing developing eVTOL (electric vertical take-off and landing) flying taxis, one report predicts that by 2040 there will be 430,000 such vehicles in operation around the world.
This comes as delivery drones are also being increasingly developed and tested, with the global market for these tipped to be worth $5.6bn (£4bn) by 2028, according to one estimate.
To handle the demands of a future, in which drones and flying taxis (think large, multi-propeller drones) share airspace over busy conurbations, proponents of the technologies say cities will need to build lots of mini-airports, dubbed "skyports".
These mini airports will be needed so that the taxis can land in the spots where people want to go.
California-based firm, Joby Aviation, is at the forefront of developing flying taxis, having now carried out more than 1,000 test flights of its eVTOL craft.
It hopes to get approval from US regulator, the Federal Aviation Administration (FAA), to begin commercial operations in 2024.
Joby's piloted vehicle can carry four passengers, travel at up to 200 mph (322 km/ph), and has a range of more than 150 miles (241km).
"We envisage offering our aerial ride-sharing service from locations near to where people live, work and want to go," says Oliver Walker-Jones, a spokesperson for Joby.
"We are working closely with cities to ensure our service connects to other modes of transit, co-locating skyports with train stations, airports and other hubs."
Joby has already partnered with US parking firm Reef Techology with the aim of turning the roofs of some of its carparks into skyports. And it has signed a similar deal with property business Related Companies, New York's largest landlord.
"With these partners, we aim to build out skyports in initial launch markets that offer attractive savings on routes with high existing demand and frustrating levels of congestion on the ground," adds Mr Walker-Jones.
The bosses of Joby Aviation hope to be able to start commercial flights of their flying taxi in 2024- photo collected
While a network of skyports may seem far-fetched, the concept is already receiving considerable positive attention from a number of US city administrations.
Houston, Los Angeles, and Orlando have already announced plans to establish infrastructure for flying taxis and other similar vehicles.
Los Angeles mayor Eric Garcetti says the proposals for his city will "provide a template for how other local governments can take this new technology to even greater heights".In the UK, plans to build the country's first skyport in Coventry near the city's rugby and football stadium have the backing of the British government.
Seeking to become the world's first operational hub for air taxis and cargo drones, it is being designed by a Hyundai-backed UK company called Urban Air Port (the firm has registered the name as a trademark).
Billed as the "world's smallest airport", the firm hopes that the zero-emissions facility will be replicated around the globe to cut both road congestion and air pollution from cars and lorries.
"Existing airports around the world are huge, and carbon hungry, with 1.2km runways," says Urban Air Port founder and executive chairman Ricky Sandhu. "That's because of the technology and how the aircraft take off and land.
"[By contract], new vehicles can take-off vertically and land extremely accurately. There's going to be a whole new type of infrastructure needed to support those."
Mr Sadhu adds that the initial site in Coventry - which is expected to become open in early 2022 - will serve as a "logistics demonstration."
The project's designers believe that the concept will show how a network of small urban mobility hubs can be rapidly set up in cities of various sizes.
"Our goal is to show that the turnaround time can be absolutely minimal, so that with a very small footprint, you can get high-capacity infrastructure that can support the vehicles," Mr Sadhu said.
Experts, however, point to several challenges that stand in the way of flying taxis and skyports really taking off.
"Whether and when we reach a point reminiscent of the Jetsons will depend on how the industry handles a number of key hurdles," says Jennifer Richter, a Washington-DC based lawyer who specialises in the law surrounding drones and air taxis.
"These include public acceptance, high-volume manufacturing, digital, power and physical infrastructure investment, and the development of a highly-automated air traffic management system."
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Michael Taylor, a travel and technology expert at US business research group JD Power, says the main challenges are regulatory hurdles and air traffic control systems.
"Imagine the regulation of air traffic routes, and then multiply that by a million," he says.
"It's likely to start by establishing standard drone, or air taxi routes. Rules will be set, kinks worked out, and standards applied universally to minimise incidents."
Regarding regulatory hurdles, the biggest barrier is that flying taxis have yet to be given authorisation to fly commercially by the relevant authorities, such as the Federal Aviation Administration (FAA) in the US, or the UK's Civil Aviation Authority (CAA).
Both of these are, however, continuing to study the issue - the safety of such vehicles, and how authorisation can be formulated and subsequently monitored. At the CAA this work is being done by a specific innovation team.
Aaron Belbasis, an expert in emerging technology at engineering and design firm Aurecon, says that the health and safety issues are paramount.
He points out that with more motorised vehicles in the air it is a statistical probability that more accidents will occur, adding that if a flying taxi fell in an uncontrolled way it "could amount to a descent with as much aerodynamic finesse as a rock, posing great danger to all on-board, and anyone or anything in the direct parabolic vicinity of the vehicle".
Ricky Sadhu says his main concern is that investment in skyports and other infrastructure may lack behind investment in the eVTOL vehicles themselves.
"I'm less concerned about regulation. What we're seeing is evolving quickly," he says.
Mr Sadhu says that despite the challenges, there is already enormous demand and interest in skyports from cities across the US, Europe and Asia.
"We're aiming to see 200 Urban Air Ports deployed within the next five years, globally," Mr Sadhu added. "But we think that's conservative, because big cities will need significantly more."
BDST: 1321 HRS, OCT 19, 2021