Usually, squeaking significant extra mileage out of a vehicle involves some very conspicuous changes. You can switch to a new engine, go hybrid (or full electric), or build components out of lightweight materials like carbon fiber. GM, however, is trying something different with the just-launched 2017 GMC Acadia: glue. Rather than join the SUV's underbody components using rivets or welds, GM is using aircraft-grade adhesives along the seams to create a body so stiff that the company can afford to use thinner steel. The result is an Acadia that's a whopping 700 pounds lighter than its predecessor, giving it 23 miles per gallon (versus the 2016 model's 18) without having to resort to more drastic changes.
As the New York Times observes, though, car makers are pursuing unusual assembly tricks like this out of necessity. The US wants brands to reach an average of 54.5MPG by 2025, and that means improving fuel economy across as many models as possible -- including big, gas-guzzling SUVs where hybrid and electric motors aren't always practical. The falling costs of electric cars may reduce the urgency behind using glue or other uncommon efficiency tricks, but GM probably doesn't want to take any chances.