Short answer
A heavy truck idling with air conditioning can burn over a gallon of diesel an hour, and Gulf temperatures push that figure higher. Measuring it correctly needs an ignition-based, zero-speed definition and an idle-hours counter, but the measurement only becomes savings once it reaches the driver in real time, tied to an incentive.
Key takeaways
- Idling fuel burn varies enormously by vehicle class, from under a fifth of a gallon per hour for a car to over a gallon for a truck running AC.
- Gulf ambient heat raises AC load, and DOE/EPA data shows AC can cut fuel economy by more than 25% under very hot conditions.
- EPA's own idle emission factors state they do not apply to long-duration "hoteling" idling, the exact case a stationary Gulf truck represents.
- SAE J1939 tracks idle hours and idle fuel as separate counters from total engine hours, which is what makes idling measurable at all.
- A dashboard in an office changes nothing. Savings require a real-time, in-cab signal tied to an incentive.
01What idling is, in data terms
Idling, for measurement purposes, is a specific combination of two conditions: ignition on, and vehicle speed at zero. Teltonika devices determine the zero-speed half from a movement source, GNSS reports moving if a fix exists and speed is at least 5 km/h, or CAN reports moving if the vehicle bus speed is above zero, and gate the whole calculation on ignition status, itself derived from power voltage, digital input, or engine RPM read from OBD-II or CAN. The Excessive Idling scenario built on top of this starts its clock once the vehicle has been stopped for a configured time and clears once movement resumes for another configured time, with defaults that differ by device family. Getting these definitions right is the whole basis for a trustworthy idling report; get the ignition source wrong and every downstream number is wrong with it.
02How much fuel idling actually burns
Argonne National Laboratory's Idling Reduction Savings Calculator publishes idle fuel-use rates by vehicle class that make the scale of the problem concrete. A Class 8 tractor-semitrailer at 80,000 lb GVWR burns about 0.64 gallons per hour with no accessory load, rising to about 1.15 gallons per hour with air conditioning running. A medium heavy truck in Class 6-7 burns about 0.44 gallons per hour unloaded. A delivery truck in Class 5 burns 0.84 gallons per hour unloaded and 1.11 with a load. Even passenger cars are not negligible at scale: a 2.0-litre gasoline car burns roughly 0.16 gallons per hour idling unloaded, rising to 0.29 with a load. These are Argonne's own reference figures, not vendor claims, and they are the numbers a fleet should benchmark its own idling cost against before assuming a savings estimate from a telematics dashboard.
03Why the Gulf case is worse
Every idling figure above assumes a specific accessory load, and the accessory that dominates in the Gulf is air conditioning. The US Department of Energy's official fuel economy resource states that AC use can cut a conventional vehicle's fuel economy by more than 25% under very hot conditions, a figure measured for ordinary driving, and one that applies with even more force to a stationary, idling vehicle where the engine's only job is running accessories rather than moving the vehicle. Argonne's technical analysis of idling reduction technologies separately found that diesel trucks running cab heating or air conditioning at idle burn about one gallon per hour at a modest 5 brake-horsepower accessory load and 1,000 rpm, and noted explicitly that the rate is not a constant, since it varies with the actual accessory load and engine speed a driver chooses. A Gulf summer, where cab cooling is not optional, sits at the high end of every one of these ranges.
04Necessary idling versus waste
Not every idle minute is waste, and treating all of it as a policy violation invites drivers to defeat the measurement rather than change behaviour. A driver waiting at a loading dock, running a refrigerated compartment, or cooling a cabin before a delivery in extreme heat is idling for a reason a fleet policy should accommodate. The distinction most anti-idling regulations draw is duration and context rather than a blanket ban: California's regulation for buses and commercial vehicles allows idling but limits it to no more than five consecutive minutes or periods aggregating more than five minutes in an hour, while Connecticut's school bus rule sets a three-minute limit but explicitly exempts idling when the outdoor temperature is below 20°F and heating or cooling is necessary. A measurement framework that cannot separate a two-minute loading stop from forty minutes of unattended idling will misclassify both.
05Measuring it correctly
The instrument matters as much as the policy. Teltonika's Excessive Idling scenario is disabled by default and requires two thresholds to be set: time to stopped, which determines how long the vehicle must be motionless before an idle event starts, and time to moving, which determines how long it must move before the event clears. The FMC003 and FMC920 family defaults these to 5 and 2 seconds respectively, deliberately short, because they are tuned for detecting movement transitions rather than idling waste, while the FMC650 defaults to a 300-second (5-minute) stopped threshold and a 5-second moving threshold, which is closer to what a fuel-waste policy actually wants to trigger on. Whichever device is used, the stopped threshold should be set to match the policy's own tolerance, for example California's five-minute figure, not left at a factory default chosen for a different purpose.
06The engine-hours counter as the cross-check
A separate, standards-defined instrument exists for cross-checking an idling policy at the fleet level rather than the single-event level: SAE J1939 defines SPN 235, Engine Total Idle Hours, and SPN 236, Engine Total Idle Fuel Used, transmitted together in PGN 65244, the Idle Operation message. SPN 235 accumulates at a resolution of 0.05 hours per bit and SPN 236 at 0.5 litres per bit, both separate counters from SPN 247, Engine Total Hours of Operation, which accumulates regardless of whether the engine is idling or driving the vehicle. A fleet with access to this CAN data can compare a vehicle's idle-hours fraction of its total engine hours over a month, independent of any GPS-based event log, which is a useful audit against the ignition-based measurement described above.
07Why correct measurement does not become savings
This is the point the owner's view is built on, and it is the single most common reason idling programmes disappoint. A dashboard showing idling hours and fuel waste in a manager's office is a correct measurement that has not yet reached the person who can act on it, the driver, in the moment the engine is idling. The information arrives days or weeks later, disconnected from the specific decision that produced it, and nothing about seeing a report changes what a driver does tomorrow. Idling falls when the same information reaches the driver in real time, through an audible or visual in-cab alert, and when the resulting saving is tied to a tangible incentive at the end of the reporting period. Data without a real-time nudge and a behavioural change in the field is simply a well-produced report describing continuing financial waste.
08The in-cab feedback loop
Building the loop that actually works starts with moving the alert from the office to the cabin. Teltonika's Excessive Idling scenario supports a configurable SMS event text, defaulting to "Idling Event", that can be sent the moment the stopped threshold is crossed, and the same event can trigger any in-cab notification the fleet's platform supports. The design goal is a signal the driver notices at the moment the behaviour is happening, not a line in next week's report. Pairing this with a short grace period that matches the fleet's own operational reality, long enough to cover a legitimate loading stop, short enough to catch unattended waste, is what turns a correct measurement into a correct nudge.
09Incentives, and how they go wrong
The second half of the owner's loop is tying the saving to something the driver values, and this is where a well-measured programme most often collapses back into a report nobody reads. An incentive built on a raw idling-minutes count repeats the same fairness problem that undermines harsh-event scoring: a driver whose route requires more legitimate stationary time will always show more idling minutes than one who does not, whatever the actual waste. The incentive needs the same normalisation the measurement needed, idling minutes as a share of total engine hours, or against a route-matched baseline, not an absolute count compared across dissimilar duty types. An incentive that punishes route assignment rather than behaviour earns the same resentment a punitive ranking does, and produces the same result: drivers who stop trusting the system and start defeating the sensor instead of changing the behaviour.
10Idle reduction targets that are achievable, not punitive
A target set from the wrong baseline sets a programme up to fail on day one. Long-haul US truck data from Argonne brackets truck idling behaviour into roughly 1,000 to 2,000 hours per year of displaceable idling, distinguishing what Argonne terms "low idlers" from "high idlers" within that range, and a truck that idles this much accumulates its own separate cost, since DOE notes that where manufacturer warranties and maintenance intervals apply to hours operated rather than miles travelled, the cost of idling is greater than fuel alone. Rather than adopting a foreign benchmark unchanged, use it to sanity-check a target derived from your own fleet's measured baseline over the first period of correct measurement, then set a reduction target, not a zero-idling target, which every driver will read as unachievable and therefore ignore.
11What the data cannot tell you
A stated limit belongs here as much as anywhere else in this cluster. An ignition-and-zero-speed idling record tells you that a vehicle was stationary with the engine running for a given duration. It does not tell you why. It cannot distinguish a driver waiting on a loading dock from one taking an unauthorised break, or a genuinely necessary cabin-cooling stop in extreme heat from a habit of leaving the engine running out of convenience. The EPA itself draws a related boundary explicitly: its idle emission factors are stated not to apply to long-duration hoteling idling, where the engine may run for hours with accessories active, because the short-idle test conditions the factors were derived from do not represent that case. Reading the reason behind an idling event still requires a route review or a conversation, the same as a harsh-event outlier does.
12Reporting period and seasonality
Idling data read over too short a window misleads in a specific, predictable direction in a Gulf climate: a summer week will show materially higher idling-fuel figures than a winter week for the same fleet running the same routes, purely because AC load rises with ambient temperature, the Argonne idle-rate-by-class table itself is published as separate with-AC and without-AC figures for exactly this reason, and the gap between them is not a rounding error. Comparing a summer measurement against a winter target, or against a benchmark measured elsewhere in a different season, will read as a policy failure that is actually a climate effect. Reporting idling cost on a rolling twelve-month basis, or explicitly season-adjusted, keeps the measurement honest and keeps a driver's incentive from being penalised for a July shift that a January shift would never have produced in the first place.
13How ENTEK.AI positions idling measurement
ENTEK.AI treats idling as a measurement problem and a behaviour problem that need two different pieces of design, not one dashboard doing both jobs. On the Fleet screen, a vehicle that is stopped with its engine on is shown as idling, next to the vehicles that are moving, parked or offline, so a supervisor can see who is idling now. The in-cab alert that changes driver behaviour is a separate piece, set on the tracker itself. We do not have a published figure for how much fuel our own deployments have saved through idle reduction, and rather than present an unmeasured estimate, we say plainly that the saving depends entirely on whether a fleet closes the loop the owner describes, real-time signal, tied to an incentive, because the measurement alone, however accurate, has never been the part that saves fuel.
| Vehicle class | Idle rate | With AC / heating |
|---|---|---|
| Class 8 tractor-semitrailer | 0.64 gal/h | 1.15 gal/h |
| Transit bus (Class 7) | 0.97 gal/h | not separately published |
| Medium heavy truck (Class 6-7) | 0.44 gal/h | not separately published |
| Delivery truck (Class 5), with load | 1.11 gal/h | not separately published |
| Passenger car, 4.6 L gasoline, with load | 0.59 gal/h | included in AC fuel-economy loss figure |
| Passenger car, 2.0 L gasoline, no load | 0.16 gal/h | AC use can cut economy >25% in extreme heat |
Idling fuel burn by vehicle class
Comparison table in this article; truck figures from Argonne National Laboratory, Idling Reduction Savings Calculator
Figures and sources
- Idling fuel use, Class 8 tractor-semitrailer, no accessory load: 0.64 gal/h (≈2.42 L/h) (Source: Argonne National Laboratory, Idling Reduction Savings Calculator, as of 2026-08-31)
- Idling fuel use, Class 8 tractor-semitrailer, with air conditioning: 1.15 gal/h (≈4.35 L/h) (Source: Argonne National Laboratory, Idling Reduction Savings Calculator, as of 2026-08-31)
- Idling fuel use, medium heavy truck (Class 6-7), no load: 0.44 gal/h (≈1.67 L/h) (Source: Argonne National Laboratory, Idling Reduction Savings Calculator, as of 2026-08-31)
- Idling fuel use, delivery truck (Class 5), no load and with load: 0.84 gal/h no load; 1.11 gal/h with load (Source: Argonne National Laboratory, Idling Reduction Savings Calculator, as of 2026-08-31)
- US DOE Alternative Fuels Data Center assumed idling rate for long-haul trucks: 0.8 gal/h (≈3.03 L/h) (Source: US DOE Alternative Fuels Data Center, as of 2026-08-31)
- Argonne finding on diesel idling fuel burn with cab heating or AC operating: ≈1 gal/h at 5 bhp accessory load and 1,000 rpm (Source: Argonne National Laboratory, ANL/ESD-43, as of 2026-08-31)
- DOE/EPA figure for how much AC use can cut fuel economy in very hot conditions: more than 25% (Source: fueleconomy.gov (US DOE / US EPA official site), as of 2026-08-31)
- EPA average idle emission rate, heavy-duty diesel vehicles: NOx: 33.763 g/hr (Source: US EPA Emission Facts EPA420-F-08-025, as of 2026-08-31)
- EPA caveat: idle emission factors do not apply to long-duration hoteling idling: explicitly stated as not applicable (Source: US EPA Emission Facts EPA420-F-08-025, as of 2026-08-31)
- SAE J1939 SPN 235, Engine Total Idle Hours, resolution: resolution 0.05 hr/bit, in PGN 65244 (Source: SAE J1939-71 (Revised MAR2011), Vehicle Application Layer, as of 2026-08-31)
- SAE J1939 SPN 236, Engine Total Idle Fuel Used, resolution: resolution 0.5 L/bit, in PGN 65244 (Source: SAE J1939-71 (Revised MAR2011), Vehicle Application Layer, as of 2026-08-31)
- Teltonika FMC003/FMC920 Excessive Idling default thresholds: time to stopped 5 s; time to moving 2 s; scenario default disabled (Source: Teltonika Telematics Wiki, FMC003 Parameter list, as of 2026-08-31)
- Argonne bracket for long-haul truck displaceable idling hours per year: ~1,000 to 2,000 h/yr (Source: Argonne National Laboratory, Economics of Idling Reduction Options, as of 2026-08-31)
- California anti-idling regulation limit for buses and commercial motor vehicles: no more than 5 consecutive minutes, or 5 minutes aggregated per hour (Source: California Code of Regulations §2480, as of 2026-08-31)
Questions
How much fuel does idling actually cost a Gulf fleet?
It depends heavily on vehicle class and AC use. Argonne's reference rates run from about 0.16 gallons per hour for a small car to over 1.1 gallons per hour for a loaded truck, and DOE data shows AC alone can cut fuel economy by more than 25% in very hot conditions, which describes most of the Gulf operating year.
Is all idling waste that should be eliminated?
No. Loading stops, refrigerated compartments and cabin cooling before a delivery in extreme heat are legitimate. Most anti-idling regulations reflect this by limiting duration rather than banning idling outright, California allows up to five minutes per hour for commercial vehicles.
Why does an idling dashboard not reduce fuel cost on its own?
Because the information reaches a manager's office days later, disconnected from the moment the driver made the decision. Reduction requires a real-time in-cab signal and an incentive tied to the outcome, the measurement alone changes nothing in the field.
How should idling targets account for the Gulf summer?
Report on a rolling twelve-month basis or season-adjust the target. A summer week will show materially higher idling-fuel figures than winter for the same routes, purely from AC load, comparing summer data against a winter-derived target reads as a policy failure that is actually a climate effect.