China added more than 2 million kilometers of road in the past two decades, encouraging personal vehicle usage. Photo by Joe Dunckley.

The vast majority of emissions come from the lifetime use of the vehicle, says Lee Schipper, director of research for EMBARQ, the World Resources Institute's transportation program.

Developing cars powered by hydrogen will be an effective way to relieve China's gas pollution problems, experts say.

Under the pilot project, a dozen 2001 model buses were fitted with particle traps and fueled with ultra-low sulfur diesel, or ULSD, which was imported for the test. Particle and carbon monoxide emissions were lowered by 90 percent, and emissions of nitro

According to a variety of transportation experts, motorization is soaring everywhere, with the fastest growth occurring in Asia and Latin America. The result could be serious environmental and social disruptions throughout the world.

Smart government policy, not just new technology, is required to address climate change. The Metrobus system in Mexico City is a good example of a low-tech solution that significantly reduces emissions.

Overview of the Bus Rapid Transit system in Mexico City, known as Metrobus.