How much does idling cost a fleet?

How much fuel does idling burn?

Idle fuel use depends mostly on engine size and on what's running: heater, air conditioning, lights, upfitted equipment. Two public measurements bracket a typical light-duty vehicle:

The litres-per-hour figures are our conversions (0.279 mL/s × 3,600 s ≈ 1,004 mL/h; 300 mL × 6 = 1.8 L/h; 1 US gallon = 3.785 L). Argonne's own caveats matter: its figure comes from one car at one temperature. It says hot and cold weather "are likely to affect results, as are the loads required to supply passenger comfort." A bigger V8 pickup or a van running a heater on a −20 °C morning will likely burn more than either figure (our inference). Treat 1.0–1.8 L/h as a starting range for cars, SUVs and light vans, not a measurement of your own vehicles.

What that costs a fleet

The price of fuel changes every week, so the worked example below shows litres first and then the cost at a few round pump prices. For your own numbers, use your local price: Statistics Canada publishes monthly average pump prices for gasoline and diesel by city.

A worked example, with our assumptions stated:

• 30 minutes of idling per vehicle per working day;
• 250 working days a year;
• idle fuel use of 1.0 to 1.8 L/h, from the table above.

This is our arithmetic, not a published figure: 0.5 h × 250 days = 125 idle hours; 125 h × 1.0–1.8 L/h = 125–225 L; then litres × price, rounded to the nearest $10. The prices are round examples, not quotes. For diesel vehicles we use the same 1.0–1.8 L/h range, because we haven't found a published idle rate for light-duty diesels; that is our assumption, not a measurement. Scale it to your own fleet: litres per hour × idle hours per year × your local pump price. Half an hour a day is only our assumption. Warm-ups, waits at job sites and breaks in the cab can add up to more or less, so measure your own before you budget.

The hidden cost: engine hours

Fuel is the visible cost. Idle hours also count toward oil changes on some vehicles. Ford's 2020 Super Duty owner's manual says, in its scheduled maintenance section, that "for every hour that your vehicle idles, it accumulates the equivalent of approximately 25 mi (40 km)," and its maintenance table lists extended idling as a severe-use condition.

On that truck, 125 idle hours a year (our example above) would count as about 5,000 km (3,125 mi) toward oil changes, distance that never shows on the odometer. That's our arithmetic from Ford's figure (125 × 40 km); Ford states it for oil life, not overall wear, and other makers may count idle time differently. See how to schedule preventive maintenance.

Turn it off: the 10-second and 60-second rules

• The physics: 10 seconds. Argonne found, restarting a warmed-up test car at 21 °C, that "fuel use and carbon dioxide emissions are always greater for idling over 10 seconds" than for restarting. NRCan's model idling by-law says the same of a light-duty car, and notes that "a number of municipal and corporate fleets have imposed 10-second limits on idling of fleet vehicles."
• The practical rule: 60 seconds. NRCan's everyday advice is to "turn off your engine when you're stopped for more than 60 seconds, except when in traffic."

Vehicles with automatic engine stop-start already do this at lights. The savings a fleet can still make are mostly outside traffic: at job sites, loading docks and during breaks (our observation).

Winter: warm up by driving, not idling

In a Canadian winter, the urge is to let the van run for 15 minutes. NRCan's model by-law says that, in general, "it is more polluting to idle a vehicle to warm up the engine than to start driving after about 30 seconds from a cold start." Engines "warm up fastest when a vehicle is being driven, so as long as the windshields are clear, there is little reason to idle on start-up." It adds that a block heater in very cold weather "warms the engine before starting and reduces pollution even more."

So the fleet winter routine is: plug in the block heater on a timer, clear all the glass, and drive off gently. Our guides on when to plug in a block heater and why batteries die in the cold cover the details.

Safety first. Idling is sometimes the right call: in traffic, to keep windows clear, or to keep a person warm in dangerous cold. Never run an engine in a closed garage or bay, where carbon monoxide builds up. Never leave a running vehicle unattended where a by-law forbids it.

Idling by-laws

Many Canadian municipalities limit idling. Toronto's Idling Control By-law "limits idling to no more than one minute in a 60-minute period." Chapter 517 of the municipal code lists the exceptions. They include police, fire and ambulance vehicles in operations or training, mobile workshops while being used for their basic function, and vehicles held motionless by an emergency, traffic, weather or mechanical trouble beyond the driver's control. Its definition of idling also leaves out an engine running auxiliary equipment essential to the vehicle's basic function. We checked Toronto only; limits and exceptions vary, so check each municipality your vehicles work in.

How to measure your fleet's idling

You can't manage what you don't measure. Options, from simplest:

1. Ask and observe. A week of drivers noting warm-up and waiting times gives a first estimate.
2. Read engine data. Through the OBD-II port, engine speed above zero with vehicle speed at zero is idling, so a logger can total idle time (our inference from the required data). California's OBD-II rule, 13 CCR § 1968.2, also requires an engine fuel rate signal on 30% of 2019, 60% of 2020 and all 2021 and newer vehicles certified to it, which lets idle fuel be measured rather than estimated (our inference). See what OBD-II data can tell a fleet manager.
3. Set a policy and share results. A clear rule (off after 60 seconds except in traffic, 30-second winter warm-up) plus monthly idle totals per vehicle.