The first hybrid buses hits the streets of New York City almost ten years ago and the National Renewable Energy Laboratory has just done a follow-up study to evaluate the second generation. The newer buses were compared to the original Orion VII hybrid units. The more recent buses were found to actually consume 6.8 percent more fuel than the first generation buses due to the EGR system that was added in 2004 to help reduce emissions. However, improvements in the design including a simpler cooling system and battery control system resulted in a 40 percent reduction in maintenance costs and a 24 percent reduction in operating costs. One example of the savings from the hybrid buses is the cost of brake maintenance. Because the hybrid buses use regenerative braking extensively, the buses are able to go more than twice as far between brake lining replacements. The buses currently in use in New York use lead acid batteries while the next generation of Orion buses will switch to lithium ion.
[Source: National Renewable Energy Laboratory]