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, greenhouse gas emissions have fallen, likely due to legislation requiring that retail diesel contain some blended non-fossil diesel (biodiesel can be made from plant oils, animal fats, and even cooking oil from restaurants), 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. The discrepancy is not simply in the PlanZero estimations, it exists between the NEUD and the NIR: for example, the GHG estimates in the NEUD for year 2023 were approximately 9Mt${\mathrm{C}\mathrm{O}}_2\mathrm{e}$ and 32Mt${\mathrm{C}\mathrm{O}}_2\mathrm{e}$ respectively from diesel in medium-duty and heavy-duty freight trucks. Urban buses contribute an additional 1.4 Mt${\mathrm{C}\mathrm{O}}_2\mathrm{e}$. Diesel GHG emissions from these three NEUD-categories totalled 42.4Mt ${\mathrm{C}\mathrm{O}}_2\mathrm{e}$), exceeding the NIR emissions estimate for heavy-duty diesel vehicles in that year (36.2Mt${\mathrm{C}\mathrm{O}}_2\mathrm{e}$) by 6.2 Mt, or 17%. I reduced this gap in PlanZero by removing the use of biofuel and renewable-derived diesel, but it made only a small difference and most of the gap remains. The methodology in the NEUD Handbook appendix B seems sensible; I do not know which buses, or medium, or heavy-duty trucks, should not be counted in this IPCC-defined sector; they all seem like heavy, diesel-burning road vehicles whose exhaust emissions should be counted. Perhaps the mystery will resolve itself after future work if I model e.g. off-road vehicle diesel use and find myself with an under-estimate that balances things out.

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 (not easy, these are already major logistics cost drivers)
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 long-haul freight are (1) dropping speed limits for freight vehicles and (2) 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, but perhaps to flatten after 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 long-haul 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. Long-haul freight EVs are commercially available, but to use these at scale will require grid capacity upgrades and advances in battery chemistry at commercially viable price points. 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 short-distance freight and buses, strategies for decarbonization are more advanced. Short-distance freight can be done on today's EV batteries. Relative to long-haul 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 an estimator of emissions from heavy-duty diesel vehicles based on data from NRCan's National Energy Use Database. The estimator over-estimates GHG emissions by 3-10 Mt ${\mathrm{C}\mathrm{O}}_2\mathrm{e}$ and I don't yet have a hypothesis as to why; I only hope that after estimating some off-road diesel usage things may balance out. 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 (about 5% of the national total).

Until then,

- James Bergstra

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