In 1995, Argonne National Laboratory developed a simplified formula for calculating the cost of truck engine idling. Today, virtually every manufacturer of devices and systems for reducing engine idling also offers a formula, or even an online calculator, designed to help fleets compare current per-vehicle idling costs (fuel, maintenance and engine wear) with the costs of installing and using their particular equipment.

Try Argonne's generic formula or one of the product-specific versions and the bottom line will be basically the same, however. Idling doesn't just contribute to air pollution and squander limited resources; it burns up profit at a truly amazing rate.

COST OF IDLING CALCULATION

Locate your engine rpm and parasitic brake horsepower per hour (bhp/hr.) at idle on this chart. Typical accessories use between 10 and 20 bhp/hr. during idling. The adjacent number (expressed in gallons per hour) is an estimate of your per-vehicle fuel consumption while idling. For example, at 1,000 rpm and 10 bhp/hr. for accessories, a typical diesel engine consumes fuel at the rate of 1.2 gal./hr.

RPM	Parasitic bhp/hr. for accessories
	0	5	10	20	30
800	0.6*	0.7	1.0	1.4	1.7
1,000	0.75	1.0	1.2	1.55	2.0
1,200	1.0	1.2	1.5	1.8	2.25
*gallons per hour

1. Estimate the number of idling hours per year that could be eliminated by using one or more of the available engine idling alternatives to provide HV/AC and power auxiliary devices. Hours per year ______

2. Multiply the hours-per-year number by the appropriate number from the table to calculate the total number of gallons of diesel used per year during idling. Gallons per year ______

3. Multiply gallons per year by the average cost of diesel fuel/gal. to determine the cost of fuel for idling per year. Cost of fuel for idling $______ per vehicle/per year

4. Multiply the number of idling hours per year by 0.4 to calculate the additional expense per year idling contributes to vehicle maintenance costs (oil/filter changes). Maintenance costs for idling $______ per vehicle/per year

5. Multiply the number of idling hours by 0.8 to calculate the costs for additional engine overhauls due to idling-caused wear. Engine wear costs $______ per vehicle/per year

6. Add the fuel costs, preventive maintenance costs and engine overhaul costs to determine the total per year cost of idling each truck in your fleet. Total cost per truck/per year for engine idling: $______