LightImpact: An open-source model for quantifying energy savings of lightweight vehicles in life cycle assessments

Decarbonizing transport is essential to achieving global carbon neutrality targets, yet the emission savings of lightweight vehicles remain systematically underestimated in environmental assessments. In life cycle assessment (LCA) practice, these savings are typically represented by quantifying energy reduction values (ERVs) - the fuel or electricity saved per 100 km and 100 kg of vehicle mass reduction. Existing ERV estimation methods, however, rely on outdated driving cycles, static work-to-consumption conversion factors, black-box simulations, or class-averaged regressions - restricting their accuracy, transparency, and relevance to modern internal combustion engine and electric vehicles. This study introduces LightImpact, the first open-source Python library to calculate ERVs via a physics-based calculation model aligned with the current regulatory driving cycle standard and designed to overcome the methodological constraints of previous approaches. The model simulates the mass-induced mechanical energy demand from standardized driving resistances and converts it into vehicle-specific energy consumption savings using a newly developed differential efficiency factor, calibrated with manufacturer-certified consumption data. Applied to an automotive lightweight composite component case study, LightImpact yields ERVs up to 18× higher than previous estimates, revealing that the benefits of lightweight design have been systematically undermined. When integrated into LCAs, these ERVs enable more accurate evaluation of automotive lightweight components across various powertrains, regions, and grid scenarios. By bridging methodological rigor, open accessibility, and regulatory alignment, LightImpact provides a scalable model for assessing lightweight vehicles as enablers of low-carbon mobility while supporting evidence-based design decisions. • LightImpact: open-source tool to quantify energy savings from lightweight vehicles. • Enables vehicle- and powertrain-specific calculation of energy reduction values. • Reveals that past studies underestimated energy savings from lightweight design. • Sets a new standard by replacing outdated energy calculation models in LCAs. • Improves use-phase LCA accuracy to address emissions from transport systems.