Most automobiles run on petroleum fuel like gasoline. By using such fossil fuel, automobiles emit the exhaust gases such as CO² (carbon dioxide) and NOx (nitrogen dioxide). They pollute air and the pollution damages the environment of the Earth.
Researchers are developing the system to reduce the pollution and the automobiles that won’t emit the exhaust gases to protect the environment.
Low emission automobiles like hybrid buses are already commercially available.

Electric automobiles utilize electric power instead of fuel and they don’t emit the exhaust gases. They are people and earth-friendly automobiles.
Various electric automobiles are actually running as passenger cars, small passenger cars, buses and garbage trucks.

Natural gas automobiles emit less harmful gas than the automobiles running on gasoline or light oil.
Hybrid cars use petroleum fuel to run at high-speed and they run on electric power at low-speed. The researches about both automobiles have been done. And they have already become some of buses.
You may have already taken such buses to commute.