Idle Fuel Burn, Cost, and Engine-Hour Equivalent
What idling costs a truck and a fleet in fuel, and what it costs again in engine wear.
Example
You enter
- Idle hours per day 6
- Operating days per year 250
- Idle fuel rate (gal/hr) 0.8
- Fuel price ($/gal) 4.1
- Trucks in the fleet 20
- Road miles of wear per idle hour 7
- Fleet annual miles (0 to skip the per-mile line) 2200000
You get
- Annual idle hours per truck 1,500 hr
- Annual idle fuel per truck 1,200 gal
- Annual cost 4920
- Fleet cost 98400
- Engine wear equivalent 10,500 road miles per truck per year
- Added to every fleet mile 4.47 cents per mile
Checked against published worked examples from: Maryland Department of the Environment; U.S. Environmental Protection Agency, SmartWay.
Details, formula, and sources
ScopeA heavy-duty diesel at idle burns something near 0.8 gallons an hour, more with the HVAC loaded and more again on an older engine. That is a small number per hour and a very large one per year, and because idling produces no miles it is entirely absent from a cost per mile model built from fuel divided by odometer -- it silently inflates the per-mile fuel number instead of appearing as its own line. The engine-hour line is the second cost and the one fleets underestimate. Maintenance intervals are driven by engine hours as much as by miles, and an idling hour is conventionally counted as somewhere around seven road miles of wear, so a truck idling six hours a day accrues the maintenance equivalent of a substantial extra route every year and reaches its overhaul far earlier than the odometer suggests. A truck idling 6 hours a day over 250 operating days at 0.8 gal/hr burns 1,200 gallons, which at $4.10 is $4,920 a year per truck and $98,400 across a twenty-truck fleet, plus the wear equivalent of 10,500 extra miles on each one. Against 2,200,000 fleet miles the idle fuel alone adds about 4.5 cents to every mile the fleet runs, which is roughly what an auxiliary power unit or a bunk heater costs to amortize -- and that comparison is the whole point. An operating estimate; the trucks' own telematics idle data and fuel records govern.
Formula or tableannual_idle_hours = idle_hours_per_day x operating_days; annual_gallons = annual_idle_hours x idle_gph; annual_cost = annual_gallons x fuel_price; fleet_cost = annual_cost x trucks; equivalent_miles = annual_idle_hours x miles_per_engine_hour; cents per mile = fleet_cost / fleet_annual_miles x 100.
Source and editionIdle fuel burn at the engine's idle consumption rate (near 0.8 gal/hr for a heavy-duty diesel, entered rather than bundled) and the conventional engine-hour-to-road-mile wear equivalence used in fleet maintenance planning, by name. The trucks' own telematics idle data and fuel records govern.
Free accessMultiplication on the fleet's own operating figures; the idle rate and the wear equivalence are entered rather than bundled.
What governsEstimate. AHJ and licensed professional govern.
API field namesidle_hours_per_day, operating_days, idle_gph, fuel_price, trucks, miles_per_engine_hour, fleet_annual_miles, annual_idle_hours, annual_gallons, annual_cost, fleet_cost, equivalent_miles, cost_per_mile_cents
- Idle rate near 0.8 gal/hr for a heavy-duty diesel; higher with HVAC load or an older engine; entered, not bundledfleet fuel practice
- Wear equivalence an idle hour conventionally counted as roughly 7 road miles of engine wearfleet maintenance planning
- Invisible per-mile idling produces no miles, so it never appears in a fuel-divided-by-odometer cost modelfleet cost accounting