U.S. Scraps Rules That Backed Start-Stop Systems, Creating New Headaches for Automakers

Back in May 2025, Environmental Protection Agency Administrator Lee Zeldin signaled his intention to unwind one of the most debated automotive practices of the past decade: the Start-Stop system. On February 12, that effort moved forward, as the rules underpinning its scientific and regulatory justification were rescinded—effectively pulling the foundation out from under the technology.

There’s a certain irony here. The United States is now leading the charge against a feature that many drivers have already grown used to, accepting both its pros and cons. Yet the idea itself is deeply tied to American automotive history and past crises.

Many assume Start-Stop is a recent invention, but that’s not the case. As far back as 1974, Toyota introduced a similar concept in the U.S. market with the Toyota Crown. That version included a switch that shut down and restarted the inline-six engine to conserve fuel while idling. At the time, engineers estimated fuel savings of around 10 percent—no small benefit during the U.S. oil crisis.

European automakers later explored similar systems. Volkswagen developed its own approach, and by the 1980s models like the Fiat Regata offered comparable solutions. However, Start-Stop became mainstream less because of technical evolution and more due to tightening environmental regulations. Over the past decade, the system has become nearly universal, and in the U.S., brands even received regulatory credits for equipping vehicles with it.

Still, criticism has followed the technology. While it can reduce fuel consumption, it may increase wear on the engine and starter. Turbocharged engines present another concern: in certain conditions, oil circulation can stop before the turbocharger has fully cooled down—despite the unit potentially spinning at temperatures approaching 1,600 degrees Fahrenheit.

The Trump administration’s move is widely seen as a response to a segment of drivers who found the system annoying. For many, the frustration wasn’t about cost but about having to manually disable it after every restart, since the feature defaults to “on.”

Globally, however, Start-Stop systems are estimated to save roughly 3 billion gallons of fuel annually and cut carbon dioxide emissions by around 30 million metric tons. The U.S. remains one of the world’s largest sources of greenhouse gas emissions, particularly in the transportation sector.

How automakers will react remains uncertain. Many are already pivoting toward electrification, but in a market where EVs still represent a minority of sales, regulatory reversals add fresh uncertainty. Several companies—including some based in the United States—have voiced opposition to the administration’s direction. Experts at University of Washington have even compared some of the rhetoric surrounding the issue to arguments denying basic scientific principles.

Legal battles may also lie ahead. California is widely seen as a key potential challenger. There’s even discussion of a future in which a single federal emissions standard gives way to a patchwork of state and regional rules—an outcome that could make compliance significantly more complicated for automakers.