Because of steel’s low energy intensity and low GHG emissions compared to alternative materials, steel-intensive vehicles can have lower total emissions than vehicles containing high percentages of low density materials like aluminum or magnesium.
To measure the environmental impact of a product, it is essential to look at the entire life cycle of a product and the emissions associated with each stage of life.
The three major product life categories are unusually defined as the manufacturing phase, the use phase and the end-of-life (recycling) phase.
EPA is presently considering vehicle regulations for the period from 2017 - 2025. If EPA considers only the emissions during the driving phase ("use phase") of a vehicle's life, it will encourage the design and production vehicles made from materials produced and manufactured with very high green house gas emissions. This is because the emissions derived from the manufacturing of materials are not only significant component of total emissions (as shown in Figure 1) but the difference in emissions between steel and other automotive structural materials is large. A life cycle assessment (LCA) analysis performed on a lightweight (aluminum/magnesium/carbon fiber) concept vehicle developed by Lotus Engineering (in a study of variants of the Toyota Venza commissioned by the California Air Resources Board) shows the that the difference, in this case, in materials manufacturing emissions overwhelms the difference in driving phase emissions. Surprisingly, the super light alternative material vehicle had very high total emissions and the AHSS steel-intensive vehicle in the study had the lowest emissions.
This example illustrates clearly how each phase of a vehicle’s life can affect its proportion of CO2 emissions. Unintended consequences are highly likely if car companies or regulators concentrate on only one phase of the total life of a vehicle. The LCA analysis results are summarized below for the different Venza variants included in the Lotus Engineering study.
Figures 1 and 2 describe four variants of the Lotus Study: the baseline Venza [Venza], the Low-Development Case [Lotus-LD], the High-Development Case [Lotus-HD], and the High-Development Case with the AHSS body substituted into the vehicle [Lotus LD BIW in HD].
In Figure 1, GHG emissions from materials production are substantial, e.g., 29% of the total vehicle emissions. This is important as it counters a common misperception that materials manufacturing emissions are insignificant and can be ignored in vehicle regulations. As vehicle become more fuel efficient in the future, the significance of vehicle manufacturing emissions will continue to increase.
Figure 1 also shows the lowest total emissions vehicle is variant with the steel-intensive body structure [“Lotus LD BIW in HD”] which is estimated to emit 3.42 tonnes of GHG less over its life than the Lotus HD case. Considering an estimated 15 million vehicle build in 2017, this totals over 51 million tonnes of additional CO2e annual emissions, or nearly half of the steel industry’s entire annual emissions for its highest production year this decade [see below]. Further, the comparison between these two cases only considers the body structure so the use of GHG-intensive materials in other parts like, for example, closure panels will only further increase materials manufacturing emissions of the Lotus HD case and improve the total vehicle emissions advantage of the Lotus LD BIW in HD.
This comparison understates the actual difference in emissions because of considerations like the closure panels example above and the differences in the recyclability and recycling infrastructure for GHG-intensive materials, which are stated conservatively for steel in this case. At the very least it is clear that production of such vehicles from recycled material will not occur until the first fleets of vehicles are returned after their useful life, some twelve years or more in the future. Therefore, a more accurate comparison of the emissions difference for the first twelve years of production of such vehicles would be to give alternative materials intensive vehicles zero credit for recycling until end-of-life vehicles can provide it. This calculation yields 49.56 t-CO2e for the Lotus HD vehicle [12,719 plus 36,840 kg] vs. 42.1 t-CO2e for the steel case [3078 plus 39,014 kg] or a difference of 7.4 t-CO2e per vehicle.
Finally, studies done by Kendall, et. al. [Accounting for the Time Dependent Effects in Biofuels GHG Calculations, Environmental Science and Technology, 43, 7142-47] which evaluate bio-fuel impacts on land use change, found that “up-front” emissions cause greater damage to the environment due to Cumulative Radiative Forcing [CRF] and proposes these factors be accounted for using a Time Correction Factor [TCF] to deal with such temporal effects. Figure 2 applies these principles to the Lotus Study. This chart [which includes the recycling credit] shows the Lotus HD case [the lower body weight structure using GHG-intensive materials] can result in 25% more emissions, or approximately 10.9 t-CO2e per vehicle.
Lotus LD 2017
Lotus HD 2020
Lotus LD BIW in HD