Tomorrow's cities may be constructed partly out of living materials that produce energy without destroying the environment. But what will transportation look like in a world where you can't tell the difference between cities and forests? We get some hints in these gorgeous images of freeways built over forests in today's world. Imagine that these are electric cars, or even ones that are powered by hydrogen-producing bacteria, and this could just be the Earth in 200 years.

Over at The World Geography, there is a fantastic collection of "incredible drives above the trees," and these are just a small sampling of the images they've collected. Above, you can see highway H-3 in Hawaii. In the future, cities might look like an enormous green mountain, and these roadways might be leading straight to downtown.

This is today's Europa Brücke, in Austria. Beneath it, you can imagine the roofs of a city powered entirely by sunlight — and by solar cells made partly from living trees.

Brazil's Rodovia is one of the most incredible elevated highways to wind its way over the forest. But what if those hills were actually covered in bacterial mats doing water purification for São Paulo? Those trees might shelter homes, or they might be homes. The roadway could be connecting the city to its energy source, or connecting one forest city with another.

This is the Denny Creek viaduct in the state of Washington in the U.S. It's the view that we might have one day from the busy streets of our living metropolises, connected by massive viaducts that guide our shared vehicles from one high-density area to another.

FURTHER READING: Is this the city of the future?