Introducing Absolute Sustainable Lightweight Design

Absolute sustainability offers a promising approach for ensuring the needs of future generations continue to be met by setting sector and product-level sustainability targets based on the Earth’s biophysical limits. In the context of sustainability, lightweight design is considered to have an ambiguous role when it comes to analyzing its environmental benefits: while it often promotes resource conservation in the use phase (e.g., minimizing energy consumption), it can also lead to shifting impacts to other life cycle stages (e.g., complicating recycling processes). Thus, combining lightweight design with absolute sustainability could help address these trade-offs. Therefore, in this paper we introduce the concept and a definition of ‘absolute sustainable lightweight design’, where lightweighting reinforces positive environmental impacts while only allowing negative impacts within Earth’s biophysical limits. The concept is applied to five body-in-white (BIW) lightweight material concepts (conventional steel, high-strength steel, advanced high-strength steel, aluminum, and composite) for internal combustion engine vehicles in the U.S. passenger car fleet and three different sharing principles for allocating the safe operating space within the planetary boundary ‘climate change’. The results indicate that none of the lightweight BIW concepts can be classified as absolutely sustainable. Achieving absolute sustainability will require activating additional sustainability levers beyond lightweighting measures for the respective use case.