A study by a team from the University of Toronto and Ford R&D in Dearborn has found that lightweighting is an effective solution that could provide important near-term GHG emission reductions especially during the next 10–20 years when the fleet is dominated by conventional powertrain vehicles.

a) Annual US. light-duty fleet life cycle GHG emissions 2016-2050 by lightweighting scenario; (b) Annual US light-duty fleet emissions 2016-2050 showing contributions from alternative powertrain/fuel penetration, fuel consumption improvements, and Aluminum Maximum lightweighting (the blue area is the cumulative GHG emission reduction due to Aluminum Maximum lightweighting); (c) Cumulative light-duty fleet GHG emissions changes 2016-2050 due to lightweighting, showing contributions from life cycle phases. Milovanoff et al.

There is little information available on the fleet-scale GHG implications of lightweighting the U.S. light-duty fleet, or the interactions between lightweighting and technological changes such as fuel consumption improvement strategies or electrification at a fleet level. The latter gap is particularly noteworthy given the increase in vehicle efficiency and penetration of electric powertrains that may be required in the U.S. to meet the 2025 CAFE standards. We address the above gaps in the present study with the objective of quantifying the changes in GHG emissions that would result from lightweighting the U.S. light-duty fleet from 2016 to 2050.

More specifically, we evaluate the influence of electric vehicle penetration, fuel consumption improvements, fleet characteristics (i.e., average light-duty vehicle size and total fleet stock), and automotive material flow on the U.S. fleet-scale GHG emission changes due to lightweighting. Finally, we examine GHG emissions as a function of the temporal penetration of lightweighting.

—Milovanoff

For the study, the team developed a fleet-based life cycle model, the FLAME model (Fleet Life cycle Assessment and Material-flow Estimation) for the US light-duty fleet from 2016 to 2050. Four modules (vehicle, fleet, automotive material flow and LCA modules) are linked to comprise FLAME.

The FLAME model. The model is comprised of four modules (vehicle, fleet, 119 automotive material flow, and LCA modules) and is run from 2016 to 2050.

They used 12 vehicle technology categories and two size categories—cars and light trucks—to represent the US light-duty fleet. Each vehicle type is assigned a material composition (% breakdown), curb weight (kg), and fuel consumption (l or kWh/100 km) for each model year.

The vehicle material composition consists of six materials or material categories that sum to the curb weight:

1. high strength steel and advanced high strength steel (HSS/AHSS);

2. cast iron;

3. mild steel and other steels;

4. wrought aluminum;

5. cast aluminum; and

6. all other materials.

The other materials combined typically represent less than 25% of the vehicle’s weight.

The model estimates that implementation of an aggressive lightweighting scenario using aluminum reduces 2016 through 2050 cumulative life cycle GHG emissions from the fleet by 2.9 Gt CO2 eq (5.6%), and annual emissions in 2050 by 11%.

Lightweighting has the greatest GHG emission reduction potential when implemented in the near-term, with two times more reduction per kilometer traveled if implemented in 2016 rather than in 2030. Delaying implementation by 15 years sacrifices 72% (2.1 Gt CO₂ eq) of the cumulative GHG emission mitigation potential through 2050.

Lightweighting U.S. light-duty vehicles is not a stand-alone measure to decrease the fleet life cycle GHG emissions but is an effective option in the near-term that could provide important savings while the fleet is dominated by conventional vehicles.

—Milovanoff

Resources

• Alexandre Milovanoff, Hyung Chul Kim, Robert De Kleine, Timothy J. Wallington, I. Daniel Posen, and Heather L. MacLean (2019) “A Dynamic Fleet Model of U.S Light-Duty Vehicle Lightweighting and Associated Greenhouse Gas Emissions from 2016 to 2050” Environmental Science & Technology doi: 10.1021/acs.est.8b04249