Environmental concerns and rising fuel costs are driving Ontario's municipalities and fleet operators to consider alternative vehicle technologies. Elevated fuel consumption and air emissions are attributed to the unique operations of fleet vehicles and in particular, during idling. While drivers of passenger vehicles may have the option of simply not idling, fleet and emergency vehicle operators, may need to keep the vehicle operating to supply power to critical onboard equipment. These demands may be exacerbated during seasonal, temperature extremes. However, prolonged idling can impose significant environmental and economic burdens. Hybrid vehicles have yet to be utilized widely by Ontario's fleets, but there are other approaches to reduce emissions, including alternative “green” technologies to operate in-vehicle equipment and maintain fleet vehicle capabilities instead of idling. Fleet Challenge Ontario (FCO) embarked on several innovative initiatives to develop and implement a supplementary Hybrid Idling Reduction System (HIRS) to reduce the impacts from idling of fleet vehicles, and in particular police and EMS (PEMS) vehicles. The objective of the PEMS project was to demonstrate that the technology will lower idling, reduce fuel consumption, lower emissions and payback the incremental cost over the vehicle life cycle.