A hybrid electric bus combines a conventional internal combustion engine propulsion system with an electric propulsion system. These type of buses normally use a Diesel-electric powertrain and are also known as hybrid Diesel-electric buses.
The introduction of hybrid electric vehicles and other green vehicles for purposes of public transport forms a part of sustainable transport schemes.
A hybrid electric bus may have either a parallel powertrain (e.g. Volvo B5L) or a series powertrain (e.g. some versions of the Alexander Dennis Enviro400).
The United States Department of Energy (USDOE) has announced the selection of Navistar Corporation for a cost-shared award of up to $10 million to develop, test, and deploy plug-in hybrid electric (PHEV) school buses. The project aims to deploy 60 vehicles for a three-year period in school bus fleets across the nation. The vehicles will be capable of running in either electric-only or hybrid modes and will be recharged from a standard electrical outlet. Because electricity will be their primary fuel, they will consume less petroleum than standard vehicles. To develop the PHEV school bus, Navistar will examine a range of hybrid architectures and evaluate advanced energy storage devices, with the goal of developing a vehicle with a 40-mile (64 km) electric range. Travel beyond the 40-mile (64 km) range will be facilitated by a clean Diesel engine capable of running on renewable fuels. The DOE funding will cover up to half of the project's cost and will be provided over three years, subject to annual appropriations.
A report prepared by Purdue University suggests introducing more hybrid Diesel-electric buses and a fuel containing 20% biodiesel (BD20) would further reduce greenhouse emissions and petroleum consumption.