The majority of school buses in America run on diesel fuel, but those engines are far different today than the ones decades ago that spewed forth dark, black clouds of soot from the exhaust.

Estimates are that about 95 percent of the national fleet of 480,000 school buses run on diesel, but there is a growing interest in alternative fuels. Informal surveys conducted by School Transportation News indicate that the most widely-used alternative fuel is biodiesel, which commonly range in regular diesel-blend amounts from 2 percent to 20 percent.

CNG appears to be the second-most commonly used alternative fuel for school buses, especially in places like California where the Air Resources Board has required for the past two decades that all new school bus purchases be of the CNG variety. CNG has traditionally been more prevalent on the West Coast, but in recent years the fuel has expanded to the Midwest. Two of the three manufacturers of large school buses (Blue Bird Corporation and Thomas Built Buses) offer CNG options, and a third manufacturer (Starcraft) has said it would offer a CNG Type A school bus in 2011.

Meanwhile, propane has also gained ground over the past several years, especially in Texas, where the Texas Railroad Commission has introduced big incentives. Originally, propane was looked down upon by school bus operators because the system was installed as an aftermarket kit. That changed when Blue Bird introduced its Type C Vision in 2008. Thomas Built Buses also announced in November of 2010 that it would also make available a propane model.

On the small school bus front, Blue Bird developed a propane system for its Type A Micro Bird that runs on a ROUSH CleanTech system developed for the Ford E-450 chassis. Competitor Collins Bus Corporation was the first Type A school bus manufacturer to introduce propane with its solution for the Chevrolet Express and GMC Savana 3500 and 4500 van cutaway chassis, in partnership with Clean Fuels USA. Since, GM announced that it will offer propane power to all Type A school bus manufacturers that build on their built on the Chevrolet Express and GMC Savana 4500 series chassis with Vortec 6.0L engines. Plans to extend the offer to 3500 series chassis was in the works.

Hybrid and plug-in electric vehicles have also made their way onto the scene but in smaller numbers as about half of the states have at least one hybrid or electric bus in use. At this writing there were less than 1,000 hybrid or PHEV school buses in use nationwide, with the largest fleet in Wisconsin as two school bus contractors combined to run 25 of these vehicles. IC Bus introduced the first hybrid school bus in 2006. The subsidiary of Navistar offers a hybrid models utilizing an Eaton system and a PHEV using an Enova Systems solution. Thomas Built Buses, meanwhile, offers a hybrid-electric option and Collins Bus offers the hybrid option for its Type A NexBus on a Ford E-450 chassis with technology from Azure Dynamics Corporation.