The next revolution in hybrid vehicles is underway, in the stop-start world of transit buses: hybrid diesel-electrics. Around 20 percent of all transit buses are now hybrid diesel-electrics; comparatively, hybrids make up just 1.5 percent of U.S. car and light truck sales.

DaimlerChrysler's Orion brand has the lion's share of the market with almost 60 percent of hybrid diesel-electric city bus sales in North America. It offers 30-foot, 35-foot, and 40-foot Orion VII models that meet all 2007 EPA standards. The installed base of hybrid buses in North America is expected to grow by over 70 percent in the next year alone.

Hybrid diesel-electric technology really makes a lot of sense for city buses, considering that the average speed of transit buses in New York is just 7 mph. All the stopping and starting allows the regenerative breaking to keep the batteries running for longer. Along with 30 percent lower emissions and the recent introduction of ultra-low sulfur diesel (ULSD), the hybrid buses are not only efficient but eco-friendly as well.