Are Stop-Start Systems Beneficial? The Trump EPA Argues Against
Stop-start systems, a technology initially introduced as a fuel-saving measure, have become increasingly common in vehicles due to regulatory pressure to reduce carbon-dioxide emissions. According to a 2022 report from the European Commission and ACEA, these systems contributed to roughly 3%-4% of total fleet CO2 reduction between 2015 and 2020, translating into 15 to 20 million metric tons of CO2 avoided annually for a fleet of about 250 million vehicles.
The technology works by automatically shutting off the engine during stops, such as at traffic lights, reducing fuel burned and thus lowering carbon emissions. This results in real-world fuel consumption reductions of about 5 to 10 percent, which translates into proportional carbon emissions savings. The effectiveness of the system depends on stop frequency and duration, with fuel savings beginning when the engine is off for as little as seven seconds during idling periods.
In the U.S., stop-start systems are not federally mandated, but Corporate Average Fuel Economy (CAFE) standards and greenhouse-gas regulations under the EPA and NHTSA strongly incentivized their adoption, especially from the 2017 model year onward. As a result, the use of stop-start systems in U.S. vehicles has significantly increased, with the feature now included in 65% of U.S. vehicles, a marked increase from 1% in 2012.
The biggest suppliers of stop-start systems are Bosch, Valeo, Denso, Hitachi, and SEG Automotive. Society of Automotive Engineers research suggests that stop-start systems can improve fuel economy by 3% to 10% in city driving, depending on traffic patterns, engine size, and system integration.
While the overall emissions benefit is relatively modest compared to bigger shifts like electric vehicles or hybrids, the cumulative impact can be substantial. In controlled lab tests, stop-start technology reliably demonstrated reductions of 2 to 5 grams of CO2 per kilometer. Under the Top Runner Program and strict fuel-economy standards, Japanese automakers adopted stop-start systems aggressively as early as 2008, with over 90% of new cars sold in Japan by 2020 being equipped with the technology.
China's Stage V and VI emission standards also encouraged the adoption of stop-start systems. Stop-start is widely deployed in urban-focused vehicles and compact sedans in China. The global consulting firm IMARC Group values the stop-start system industry at $67 billion annually.
However, not everyone is convinced of the technology's benefits. The EPA Administrator Lee Zeldin stated that stop-start technology offers minimal carbon-emissions benefits, is widely disliked by consumers, and prematurely wears out starter systems. The EPA under the Trump Administration aimed to encourage automakers to eliminate the feature.
Nonetheless, current data supports that start-stop systems have a measurable and tangible carbon emissions benefit in everyday driving by reducing idling fuel burn. Despite some criticisms and potential regulatory changes, the future of stop-start systems remains uncertain but promising, particularly for urban driving with frequent stops.
Over the past two decades, stop-start systems have transitioned from a premium feature to a near-ubiquitous standard in internal-combustion-engine (ICE) vehicles. While they may not offer the transformative emissions reductions of electrification strategies, they represent a practical, incremental step towards a more sustainable future for conventional gasoline-powered vehicles.
References:
- European Commission, ACEA (2022)
- EPA (2023)
- Society of Automotive Engineers (2019)
- NHTSA (2017)
- Japan Automobile Manufacturers Association (2020)
- IMARC Group (2021)
- EPA (2019)
- EPA (2020)
- IHS Markit (2023)
- European Commission (2020)
Technology plays a significant role in the development of electric vehicles as well. For instance, advancements in battery technology have enabled increased range, faster charging times, and cost reductions, making electric vehicles more practical and accessible for everyday use.
Moreover, technology also facilitates the efficient operation of conventional vehicles, such as through the use of stop-start systems. These systems, which have become common in vehicles due to regulatory pressure, automatically shut off the engine during brief periods of idling, significantly reducing fuel consumption and carbon emissions.
