A vehicle lifecycle assessment study shows that cars extensively using advanced high strength steels (AHSS) emit lower greenhouse gas (GHG) emissions than aluminum-intensive vehicles.  

“We’ve done studies like this for several years, but this is the first time that we’ve had a study on vehicle lifecycle greenhouse gas emissions peer-reviewed,” Jody Hall, PhD, Vice President, Automotive Market, Steel Market Development Institute (SMDI), said in an interview with Automotive Engineering at the 2018 Chicago Auto Show.  

The SMDI study focused on five different 2016MY vehicles (sedan, sport utility, pickup truck, hybrid-electric, and battery electric). Each vehicle was redesigned as an AHSS intensive- and an aluminum intensive-body to reduce weight. “In every case, we found that lightweighting with steel was the most environmentally friendly material choice,” she said.

Representatives from Harvard University, Massachusetts Institute of Technology, Argonne National Lab, and the Stuttgart,Germany-based sustainability consulting company, Thinkstep, evaluated SMDI’s “Life Cycle Greenhouse Gas and Energy Study of Automotive Lightweighting” document.

The 10-month review and validation process confirmed the study’s conformance to the International Organization for Standardization (ISO). “The panel approved all of our methods, all of the input parameters, and all of our data sources,” Hall said.

Vehicle weight reduction has been a top priority for automakers since the U.S. Environmental Protection Agency announced a Corporate Average Fuel Economy (CAFE) requirement of 54.5 mpg for passenger vehicles by 2025. (The mpg number could be revised in the coming months.)

According to Roger Newport, Chief Executive Officer of AK Steel Corporation, when CAFE standards were established, the tailpipe became the emissions target. “But you really need to look at the total picture, instead of just a section of it,” said Newport, noting that a start-to-finish GHG emissions evaluation includes the vehicle’s material recyclability.

The SMDI study pinpoints aluminum as steel’s closest GHG emissions competitor. According to Hall, GHG emissions released during a material’s production phase can be a big part of a vehicle’s environmental footprint.

Aluminum produced in North America releases four to five times more GHG emissions than steel, noted Hall. She added that for aluminum produced globally, it’s eight to nine times more GHG emissions than steel. And, it’s about 20 times more GHG emissions versus steel to produce a kg of magnesium.

"The dramatic increase in material production emissions for vehicles that are lightweighted with aluminum instead of AHSS is never offset by emissions reduction benefits during the vehicle's useful lifetime, which is the 10-12 years that the vehicle is driven," Hall claims.