For more than 2,000 years people have wanted traveling to be easier. Ancient civilizations built early stone railroads to connect cities. Starting in the 1800s, steam-powered engines began chugging across continents-whisking passengers and freight to their destinations at speeds people had only imagined. In the 1940s, powerful diesel engines replaced steam engines. Diesel engines rely on fossil fuels. They cause air pollution and climate change. Today, electric trains are taking their place. People around the globe are experimenting with designs for trains that will change the future of transportation-making train travel quicker, cleaner, and greener than ever before.