An Auxiliary Power Unit (APU) provides a larger Array of comfort features for drivers looking to reduce idling. APU"s can provide heat, air conditioning, power for household electrical devices and engine heat. Most devices combine a small heater, a compressor for air conditioning and an alternator. APU"s may be powered by diesel fuel directly from the tractor fuel tank, or by a bank of rechargeable batteries. Diesel driven APU"s can operate for 5 hours or more on a single gallon of diesel fuel. Costs for these devices can range from $3500 to $9000, but are typically in the $6000 to $7000 range. For a partial list of manufacturers and device specifications, please visit the SmartWay website at http://www.epa.gov/otaq/smartway/idlingtechnologies.htm. For locomotives APUs automatically shut down the main locomotive engine idle while maintaining all vital main engine systems at greatly reduced fuel consumption.