In 1925, Popular Science Monthly ran this cover, which imagines what the city of the future would look like in 1950.
A few thoughts:
• The future (in 1950!) is going to be a walker's paradise! I want to live in that city — what a beautiful idea to give the top side of the transportation corridors to the pedestrian while putting the cars traffic in layers below and the electric trains a further layer below that. For this scheme to really work, the cars and trucks traveling the middle two levels would need to be emissions free, a requirement that electric vehicles would neatly satisfy.
• In the future, we'll all fly around in inflatable dirigibles. What they lack in speed when compared to jets they more than make up for in fuel economy. You can haul massive loads and large groups of people using the buoyancy of the gas balloon helped by a few small engines for maneuvering. Forget about an hour drive to the airport; in the future you'll just jump on an elevator and ride up to the rooftop airfield.
• Freight tubes will allow goods to be moved from city to city and around to shops with ease and without road-choking emissions.
• The terraced cities of the future will have rooftop green space for people to relax, play and learn in. Trees, gardens and lawns will entice citizens to linger for a moment to enjoy the greenery and will help to filter and clean rainwater falling on the city.
We didn't quite get to the green future imagined in 1925 by 1950, but maybe by 2050?