As we’ve indicated previously, there is a lot at stake with the proposed U.S. truck efficiency standards. This was made even more evident by the input from many stakeholders at the recent EPA and NHTSA public hearings in Chicago and Long Beach. One common refrain was that the proposed standards could be moved up, to take full effect in 2024 rather than 2027. Another was that technology is available to strengthen the standards, especially for engines.
Industry commenters introduced a new issue: that even U.S. Department of Energy SuperTruck tractor aerodynamics could not meet the agencies’ projections to comply with the proposed Phase 2 standards. Because we have done a lot of analysis on tractor-trailer technology generally, and on the SuperTruck projects in particular, that claim caught our attention, and we decided to take a close look at it.
There are several ways to compare the regulatory standards against the SuperTruck prototypes, including on the individual underlying technologies and on overall efficiency. So first off, here are a few basic attributes of tractors-trailers that would comply with the proposed standards, based on the technical inputs for the rulemaking.
- Engine efficiency: The agencies' Phase 2 standards would reduce fuel consumption and CO2 emissions from engines by 10% from 2010 to 2027 (4% from 2017 to 2027). The resulting average compliant engine in 2027 would have a peak brake thermal efficiency of about 49%.
- Aerodynamics: The agencies’ analysis of aerodynamic improvements to meet the proposed 2027 standard would require an aerodynamic drag-area (CdA) improvement of about 37% from the reference 2010 tractor-trailer.
- Tires: The agencies' analysis of tire rolling resistance to meet the 2027 standards includes about a 25% reduction from the 2010 reference tires.
- Overall efficiency: When including a fully compliant tractor-trailer (that is, with a compliant engine, tractor, and trailer), the Phase 2 Class 8 sleeper cab tractor-trailer in model year 2027 would be about 8 miles per gallon. This would cut tractors’ overall fuel use by about 33%.
Second, based on the various industry teams’ presentations at the U.S. DOE Merit Review conferences, here are the comparable details from the SuperTruck programs, focusing on the two programs that are furthest along, Cummins/Peterbilt and Daimler:
- Engine efficiency: SuperTruck program goals would increase engine efficiency by 20% in brake thermal efficiency. In 2014, the Cummins/Peterbilt team surpassed this goal with a 51.5% peak brake thermal efficiency. In 2015, the Daimler team surpassed this with 50.2% peak brake thermal efficiency.
- Aerodynamics: SuperTruck programs would improve aerodynamics by about 40%–50% from the 2010 baseline (the Daimler program achieved about 54%).
- Tires: SuperTruck programs would reduce tires’ rolling resistance by about 35%–40% from the 2010 baseline.
- Overall efficiency: The SuperTruck tractor-trailers have been extensively tested in 2014–2015 in a variety of representative long-haul, loaded conditions. The Cummins-Peterbilt program achieved 10.7 miles per gallon. The Daimler team achieved 12.2 mpg. These would cut tractors’ overall fuel use by about 40%–50%.
The above physical and efficiency characteristics clearly indicate how the SuperTruck programs are more technologically advanced than EPA’s standards. And this is just taking into account tires, aerodynamics, and engine technologies. There are plenty more technologies that SuperTruck has that are not being brought into the standards: for example, solar panels, hybridization, cab insulation, thermal management, advanced aftertreatment systems, lightweighting with carbon fiber, smart coasting, kinetic energy recovery systems, LED lighting, and electric turbocharging. In addition, the agencies and SuperTruck teams had differing fuel-saving approaches to minimize idling.
If only the engine, aerodynamics, and tire technologies are considered, there are just enough differences in the precise ways in which the vehicles are tested that we sought to make it truly apples-to-apples with vehicle simulations of the compliant trucks versus the SuperTrucks. Our vehicle modeling guru, Oscar Delgado, took on this question of how to precisely compare the regulatory and “Super” trucks against one another. He modeled various tractor-trailer configurations in the new EPA GEM model (Phase 2 GEM v1.0), on EPA’s newly proposed real-world test cycle (with grade). Starting from the EPA-compliant 2027 tractor-trailer, we modified it, per above, to include the SuperTruck engine, aerodynamic, and tire attributes. For consistency, we included the agencies’ adjustments for off-cycle improvements (e.g., an automated manual transmission, 6x2 driveline, etc.) in both the 2027 regulation-compliant tractor-trailer and the SuperTruck-technology equipped packages.
The figure below shows the resulting efficiency of the various tractor-trailer packages. Going down the figure shows how tractors get more efficient in the first phase through 2017, and then more efficient yet through 2027. As shown, the regulation would result in tractor-trailers that achieve about 8 miles per gallon on the new regulatory test. SuperTruck technologies would go further, delivering 9–10 mpg for tractor-trailers on the same test cycle.
Fuel consumption per ton-mile (and fuel economy in miles per gallon) of EPA compliant 2017–2027 tractor-trailers versus similar tractor-trailers with SuperTruck technology on new 65/55/transient cycle (with grade) in GEM simulation
So, when comparing with the U.S. DOE SuperTruck demonstrations, just how “Super” are the proposed US tractor-trailer standards for model year 2027? Not very. At this point, although the aerodynamic improvements are almost in the same ballpark, if the US standards are going to require technology-forcing SuperTruck-like standards for tractors, it is more likely this would be in some future Phase 3 rulemaking for perhaps 2030 and beyond.