Forum for the Future has released a new report on how the planet might look in 2040, as mankind battles to overcome challenges such as changing energy sources and an ever growing population, while taking advantage of new technologies.
The study, Megacities on the Move, says that in 30 years two in three people will live in cities, and the world's urban population will grow from 3.5 billion to 5.6 billion.
It suggests ways of overcoming transport infrastructure in such huge urban sprawls.
One idea is electric cars that can be nested together like shopping trolleys, available for people to hire from a station in one part of a city and then drive to another.
Or, if everyone owns electric cars, the stations would instead contain charged batteries that people would be able to exchange for empty ones.
All the ideas are based on models already piloted in parts of the world on a smaller scale. The stackable cars are in operation in Massachusetts, while the "switch stations" for car batteries are up and running in Denmark and Israel.
Similarly, telecommunications that enable people thousands of miles away to appear in a room, as if they were there in person are being pioneered in California.
The report also carries a severe warning: that unless action is taken now large cities risk becoming "dysfunctional environments, where people face extreme deprivation, shortages of food, water and energy, and are vulnerable to floods, heat waves and other impacts of climate change". Of four potential scenarios painted for 2040, two are negative, where transport is either limited to the rich and privileged, or heavily restricted.
Peter Madden, chief executive of the forum, said: "We are seeing the largest migration to cities in history. How those cities develop today will lock in behaviour for decades to come.
"The future wellbeing of billions of people depends on the action we take now. The global race for sustainability will be won or lost in the streets of our megacities."
Megacities on the Move was produced through a collaboration of Vodafone, sustainable transport group Embarq and the FIA Foundation, a UK charity specialising in road safety, environmental protection and sustainable mobility.The report will go to governments, city authorities and businesses to help them understand challenges of the future and develop strategies for people to live and travel more sustainably in the major cities of the 21st century.
The models of sustainable mobility are all designed to ensure that people living in cities can continue to access goods, services and information, and reach their friends and colleagues as and when they need to.
As well as the current schemes in use in the US, Israel and Denmark, the report features an electric cable car system in Medellin, Colombia, Vancouver's Downtown Travel plan consisting of 80 initiatives to encourage people to walk or cycle rather than drive, and a website in London through which people can rent out their cars when they are not using them.
The study is based on interviews with more than 40 experts on sustainable travel.
A Scottish Government spokesman said: "Scotland will undoubtedly develop to adapt to new and ever changing ways of living, working and travelling - for instance electric vehicles are likely to play a key role in future transport, run solely on electricity from the grid provided by a network of charging points."