Heavy-Duty Diesel Vehicles: Emissions Calculations

In black, the table above shows the National Greenhouse Gas Inventory (NIR), national sectoral total. The stacked shaded regions show the contributions of different vehicle types according to the National Energy Use Database (NEUD). The NIR's sectoral total and the sum of contributing factors from the NEUD show a similar shape of curve, but the sum of NEUD factors is higher by at least 3 Mt ${\mathrm{C}\mathrm{O}}_2\mathrm{e}$ (in year 2014) and as much as 10 Mt ${\mathrm{C}\mathrm{O}}_2\mathrm{e}$ (in year 2000). Both curves show a peak around years 2011-2014 when demand was rising, and emissions-reduction measures had not yet been taken. Since that time, emission has fallen, likely due to legislation requiring that retail diesel contain some blended non-fossil diesel, and requiring that new trucks be more efficient.

The discrepancy between the top of the shaded regions (the PlanZero estimator) and the thick black line (its target) is a relatively large one among PlanZero sectoral estimators. I'm not yet sure why, although two explanations are offered in the National End-Use Energy Database's Handbook. The handbook recognizes that in preparing the NEUD and the NIR (specifically NIR-2023), "Both Natural Resources Canada (NRCan) and ECCC use the energy demand data from Statistics Canada’s Report on Energy Supply and Demand (RESD) in Canada as a base." but differ in some of their category semantics, most notably for our purposes here:

1. NIR-2023 "reallocates industrial and agriculture diesel and agriculture motor gasoline to the transportation sector"
2. NEUD "reallocates diesel fuel oil use of commercial/institutional sector to the transportation sector".

I understand the first difference (point 1 above) to be that industrial and agricultural diesel use (according to either RESD or NEUD) is somewhere in "transportation" according to the NIR. Based on my understanding of the IPCC taxonomy used in the NIR, this would be some combination of this sector, and two sub-categories of "Energy / Mobile Combustion Sources / Transport / Other". I believe this diesel is counted by the NEUD as industrial use, and I'm not using it as part of the PlanZero estimator here. To the extent this NIR counts such diesel use toward this sector, the PlanZero estimator should include diesel combustion from those sources as well, which would make the discrepancy larger.

With regards to the second difference (point 2 above), I understand it to mean that diesel fuel use associated with commercial/institutional use in the RESD is counted as transportation in the NEUD. In the NIR, this diesel would presumably be counted in the area of "Energy / Mobile Combustion Sources / Transport", but not necessarily as subcategory "Road Transportation / Heavy-Duty Diesel Vehicles" (the focus of this post); in the NIR, this diesel might be counted as "Off-Road Commercial and Institutional" or "Off-Road Other Transportation". According to StatsCan's "Supply and demand of primary and secondary energy", commercial and institutional diesel use appears to be significant e.g. accounting for about 13% of national diesel usage in 2023. Spreading these emissions (currently counted by this PlanZero estimator) across multiple IPCC sectors could plausibly address the discrepancy shown in the chart above. Making this adjustment is left for future work, when developing estimators for these other IPCC sectors.

Critical Success Factors

The reduction of emissions from heavy-duty diesel vehicles seems to require some combination of the following:

1. Reduce demand for road freight (perhaps by shifting it to marine or rail)
2. Reduce the mass of freight or the distance it must travel (already a major consideration in logistics)
3. Reduce use of fossil fuels for heavy-duty vehicle applications (use other fuels, energy sources)
4. Increase energy efficiency of heavy-duty vehicles (e.g. via electric motors)
5. Reduce use of buses (without incurring greater emissions in other sectors)
6. Reduce use of fossil fuels to power buses

Barriers

• Technology Gap: Freight movement is energy intensive, in that it is almost purely the conversion of energy into propulsion to move materials from one point to another. Diesel is an affordable fuel with high energy density, there is no obvious replacement.
• Renewable Diesel: Renewable diesel fuel (e.g. B99 or B100) can currently replace diesel at a price premium of only about 25%, can be made from canola or waste cooking oil. The catch is that to make enough of it to power all heavy vehicles would require something like twice Canada's current amount of farmland, and it may not be the best use of that land.
• Batteries: Today's EV battery technology cannot carry enough charge, at low enough weight, or low enough cost, or recharge quickly enough, to support today's trucking practices without operational changes that would hurt operational efficiency.
• Grid Readiness: Freight movement needs a lot of energy. Electric truck propulsion is more energy-efficient than diesel by a factor of roughly 3x (much less energy is wasted as heat). Still, moving 2022's freight work by electricity would have required 15-20% more electricity than Canada produced in that year. (Canada produced about 560 terawatt hours of electricity in 2022 and 2023 , the freight industry used about 263 terawatt hours of energy in diesel fuel.)
• Asset Life: Heavy freight trucks are only replaced on average every 15-20 years (see stock/sales ratio, NEUD). Even compelling new technology would likely take decades to roll out across the sector.
• Charging Infrastructure: There is no technology standard or installed base of charging equipment across Canada suitable for charging heavy-duty vehicles. Several systems are in development around the world; the process of trialing and scaling one or several in Canada will take time and money.
• Geography: Canada's population is mostly spread along a thin strip of sparsely populated territory, which is one of the most energy-demanding topologies to support with a transportation or logistics network. It is also cold, which challenges many battery technologies.

Strategies

In the short term, the most promising strategies for reducing emissions in this sector are dropping speed limits for freight vehicles and blending greater quantities of renewable diesel into marketable fuel. Ontario and Quebec already require trucks to be electronically limited to 105 km/h to reduce emissions. Many countries in Europe limit freight trucks on highways to 80 km/h or 90 km/h to reduce fuel consumption and/or emissions, but beyond that there is little-to-no benefit. There's a limit too to how much renewable diesel can be produced, but as much as can be made from e.g. used cooking oil, should probably be produced and blended with fossil diesel. Renewable diesel production capacity is expected to double from 2024 levels by 2028.

It is not believed that a switch to renewable diesel, and a reduction in speed limits, can reduce the sector's emissions to zero. With regards to freight, there are many technologies in development to provide energy to freight vehicles via various novel fuels, through fuel distribution networks that do not necessarily exist yet, to be used in different kinds of engines that may or not already be used in any large-scale application. There is no reason to expect a reduction in the need for freight transportation in the years ahead. It may be a long metaphorical road to zero-emission freight sector.

With regards to buses, strategies for decarbonization are more advanced. Relative to freight vehicles, buses aren't required to move as much mass, so they don't require as much energy to travel a given distance. Electric motors are roughly 3x as energy-efficient as diesel ones on a highway, but in stop-and-go city traffic, their efficiency advantage increases, perhaps doubling again. Bus routes are often shorter than freight routes, which also lowers the battery requirements. Buses based on today's battery technologies (e.g. lithium-ion, or soon, sodium-ion) are being trialed in cities around the world, and battery powered buses seem like an increasingly practical and viable alternative to diesel ones as battery costs continue to drop (see e.g. electrification of buses in Vancouver, Toronto, and Montreal).

Conclusion

This post has introduced a estimator of emissions from heavy-duty diesel vehicles based on data from NRCan's National Energy Use Database. The estimator is too high (it over-estimates emissions) by 3-10 Mt ${\mathrm{C}\mathrm{O}}_2\mathrm{e}$ but there is a likely explanation, and the estimator can be adjusted in future work. The IPCC / Transport / Road Transportation / Heavy-Duty Diesel Vehicles page has been refreshed to feature this estimator, as well as updated critical success factors, barriers to those success factors, and strategies. The next post in this series replicating the NIR will look at stationary combustion sources in commercial and institutional applications, which was responsible for about 32 Mt ${\mathrm{C}\mathrm{O}}_2\mathrm{e}$ in 2005.

Until then,

- James Bergstra