Calculating emissions without a CAN bus

What is a CAN bus?

A CAN bus (Controller Area Network) is the internal communication network of a vehicle or machine. All electronic components, from the engine to the sensors, exchange data with each other via this network. For emission calculations, the CAN bus is particularly relevant because it delivers real-time data on, among other things, fuel consumption, AdBlue consumption and operating hours, straight from the engine.

That data is exactly what's needed to calculate emissions accurately. The problem is that not every vehicle or machine has a CAN bus, or the data isn't easy to extract. For companies with a mixed fleet of vehicles or machines, this quickly means: part of the fleet can be measured, part can't.

Why calculate emissions?

Clients in construction and infrastructure increasingly ask for this actively, for example through the CO2 Performance Ladder, where lower emissions lead to a competitive advantage in tenders. Permitting authorities and municipalities also increasingly want to know what a project actually emits, not as an estimate, but substantiated per project and period.

There's also an operational benefit. If you know what your vehicles and machines emit, you also know where fuel is being wasted and where gains can be made. Emissions data is therefore not just a reporting obligation, it's also management information. But that value only materializes once the data is complete, including for equipment without a CAN bus.

How are emissions calculated with a CAN bus?

A commonly used method calculates emissions based on CAN bus data: fuel consumption and AdBlue consumption, combined with operating hours. This approach, also known as the AUB method (AdBlue, Uren, Brandstof – AdBlue, Hours, Fuel), gives an accurate picture because it's based on the actual consumption of a vehicle or machine, rather than an estimate.

The calculation method converts that fuel consumption into CO2, and the fuel, AdBlue and hours data into NOx and NH3, per project and period, according to recognised standards such as EMEP/EEA for road transport and TNO calculation methods for mobile machinery. As long as the CAN bus data is available and reliable, this is the most accurate way to calculate emissions.

How do you calculate emissions without a CAN bus? The U-method

For equipment without usable CAN bus data, there's an alternative calculation method, developed by TNO: the U-method. Where the AUB method relies on AdBlue and fuel consumption, the U-method uses just two data points: the machine's maximum engine power and the number of operating hours. Important to know: the U-method was specifically developed for nitrogen emissions, NOx and NH3, and not for CO2.

The idea behind it is simple: emissions per hour are roughly proportional to the maximum engine power. Based on emission class (Stage class) and power range, each machine is assigned a fixed emission factor, expressed in grams of emissions per operating hour per kilowatt. Multiply that factor by the engine power and the operating hours, and you get a substantiated estimate of NOx and NH3 emissions, without ever needing fuel or AdBlue data from the machine. The coefficients behind the U-method for nitrogen oxides (NOx) were recently adjusted based on real-world measurements on dozens of construction machines, bringing the calculation closer to actually measured NOx emissions.

That makes the U-method less precise than a calculation based on actual consumption, but still useful for equipment that would otherwise fall entirely outside the reporting. Unlike nitrogen emissions, CO2 emissions are directly proportional to fuel consumption. By also estimating fuel consumption based on operating hours and engine power, a reliable CO2 calculation is therefore also possible without a CAN bus.

In practice: calculating emissions for your entire fleet of vehicles and machines

Doing this manually is still feasible for a single machine: read off the operating hours, look up the engine power, grab the emission factor and multiply. For an entire fleet of dozens or hundreds of vehicles and machines, redone every month and broken down per project, that's no longer an occasional calculation but a structural task.

With our emissions reporting, you don't have to do this manually, and you don't have to choose between equipment with and without a CAN bus either. For vehicles and machines where CAN bus data is available, Flowter calculates emissions automatically. CO2, NOx and NH3.

The result is a single report for your entire fleet of vehicles and machines, regardless of whether a vehicle has a CAN bus or not. No manually combining separate spreadsheets, no equipment left out of the picture. Simply see what the emissions are per project and period, at the push of a button.

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This article describes a situation in the Netherlands, valid as of August 2026. Situations may change. No rights can be derived from this article.