Okay, so you’ve bought a vehicle. You fill the tank and check it against the official published numbers. And it’s likely your real-world fuel economy isn’t quite as good as what the manufacturer says you’ll get.

What gives?

Better driving habits might help, but it’s partly also in how fuel economy is rated. There’s no actual driving involved – and they don’t even measure the fuel itself!

Fuel economy and greenhouse gas emissions (GHG) are intertwined – if you burn less fuel, you send fewer emissions out the tailpipe – and Canada has tightened standards on them. Automakers are required to reduce the per-mile CO2 equivalent on cars annually by 5 per cent from now until 2025, and by 3.5 per cent on light trucks, which includes SUVs.

Efficiency testing is done by the automakers, using a government-approved standardized procedure approved by the government. It’s done in a laboratory, which is the only way to ensure the consistency that’s essential to the process, and the results are submitted to Natural Resources Canada.

Each vehicle has about 6,000 kilometres of break-in on it when it’s tested, using a two-wheel dynamometer. Vehicles with four-wheel or all-wheel drive have their systems disconnected and are tested in two-wheel only. The ratings are adjusted and corrected for such things as aerodynamics, rolling resistance, weight, the four-wheel system if applicable, options, and configuration. Other factors that can affect fuel economy, such as turbocharging or hybridization, are also taken into account.

Even though you might not get the same fuel economy as advertised, you’re probably much closer than in the past. Prior to the 2015 model year, automakers only had to do two tests, simulating city and highway driving. Now there are five, which bring the fuel numbers closer to real-world performance. It also aligns Canada with the United States, which has required this “five-cycle” test for years.

The city driving test begins with a cold-engine start, as if on a summer day after parking overnight. The test chamber is between 20° and 30°C. The test simulates stop-and-go traffic, and runs for about 31 minutes with 23 stops. Average speed is 34 km/h and top speed is 90 km/h, and the vehicle idles for a total of five minutes. Toward the end of the test, the first eight minutes of the cycle are repeated, but after shutting off the engine for a short period and restarting while it’s still hot.

The highway test simulates highway and rural driving. It begins with a hot engine, and the test runs about 13 minutes with no stops. Average speed is 78 km/h with a top speed of 97 km/h, and the test chamber is the same temperature as the city test.

The cold-weather test uses the same driving cycle as the city test, but the chamber is set to -7°C.

An air-conditioning test is performed in a chamber set to 35°C, and the vehicle is tested with its A/C running. The test takes about nine minutes with five stops, and 19 per cent of the test is done while idling. The average speed is 35 km/h and the top speed is 88 km/h.

Finally, there’s a high-speed/quick-acceleration test. The engine is warm and the A/C is off, and the test chamber is 20° to 30°C. Maximum acceleration is 13.6 km/h per second, average speed is 78 km/h, and top speed is 129 km/h, with four stops.

Through all of this, no one’s checking the fuel gauge. Rather, engineers measure the carbon in the exhaust to determine how much fuel is burned. This method works for any carbon-based fuel, including gasoline, diesel, ethanol, and natural gas.

Occasionally, Transport Canada audits a manufacturer’s results. This is done if the numbers seem out of whack, and may be performed on models that haven’t been tested in a long time, or have new technologies. The feds buy the vehicles from dealerships, used standardized test fuel in the lab test, and analyze the carbon emissions to get the final figures.

If a vehicle is too big and heavy, it’s off the hook for testing. Any SUV or passenger van with a gross vehicle weight rating (GVWR, which is the vehicle’s weight, plus its maximum capacity of passengers and cargo) of more than 4,536 kg is exempt. It’s the same for other types of vehicles with a GVWR of more than 3,856 or a curb weight of 2,722 kg or above, which usually covers most heavy-duty pickup trucks.

Conventional vehicles and hybrids are measured in how many litres they use to travel 100 kilometres (L/100 km). There are separate measurements for city and highway driving, along with a combined rating that’s 55 per cent of the city figure and 45 per cent of the highway figure.

There’s also an Le/100 km rating for electric vehicles, and for range-extended or plug-in hybrid vehicles when they’re running solely on electricity. It’s an equivalency measurement of what the electric motor would use if it were running on gasoline.

You’ll find fuel ratings on the window stickers of new vehicles, or for vehicles back to 1995 at Natural Resources Canada’s website, including the original numbers and, if applicable, updated ones calculated to more modern testing standards.

So why can’t you achieve the published fuel figures? There are numerous factors, which can include cold ambient temperature, how much you use the air conditioning, and anything weighing you down, such as extra cargo or passengers.

But the most important factor is the driver. Hard acceleration and braking, speeding, and jerk throttle pressure, along with not maintaining your vehicle, will always cost you more at the pump.