MIT’s modeling shows the traffic light climate impact can drop 11–22% with eco-driving guidance via smartphones, smoothing speeds at intersections for fast, low-cost emissions cuts that complement vehicle electrification.
Traffic lights are often seen as minor annoyances during daily commutes, but their climate impact is surprisingly large—and it’s not the lights themselves causing it. Researchers at MIT found that stop-and-go driving at intersections produces up to 15% of all land transportation emissions in the United States, roughly half the emissions of the entire airline industry.
The solution, it turns out, is surprisingly simple: “eco-driving.” This system uses smartphone apps or in-vehicle displays to guide drivers on optimal speeds approaching intersections. By reducing unnecessary braking and acceleration, eco-driving can cut the traffic light climate impact by 11–22% without slowing traffic or compromising safety.
MIT’s study stands out for its scale. Using deep reinforcement learning AI, the team analyzed over 6,000 intersections in San Francisco, Atlanta, and Los Angeles, running simulations of more than one million traffic scenarios. This is nearly 10,000 times larger than any prior study of intersection emissions.
The researchers identified 33 factors influencing emissions, from road layout and vehicle age to weather and driver behaviour. By understanding these factors, eco-driving apps can suggest speed adjustments that smooth traffic, reduce fuel use, and limit emissions.
One encouraging aspect of eco-driving is that full participation isn’t required for a measurable impact. If just 10% of vehicles adopt eco-driving apps, these cars act as pace-setters, smoothing traffic for vehicles behind them and achieving roughly 25–50% of the potential total emissions reduction.
Benefits vary by city. San Francisco, with shorter distances between lights, would see smaller reductions, while cities like Atlanta, with faster roads and longer spacing between intersections, could see much larger gains. Even partial adoption of eco-driving at just 20% of intersections delivers about 70% of the potential emissions savings.
But here’s the rub: The specifics of how to modulate traffic depend on how many cars are eco-driving. For example, longer green lights hinder emissions reductions at low adoption rates but enhance them at high adoption rates. “The high-impact intersections shift as adoption levels change, which means careful planning is key,” Jayawardana, the lead author on the study, adds.
Despite these complexities, the researchers argue that eco-driving is a good strategy for reducing emissions because it rests on a technology just as ubiquitous and quotidian as stop-and-go traffic: the smartphone. And common technologies build on each other, the researchers’ calculations reveal. “While not entirely surprising, it’s encouraging to see that eco-driving complements electrification and hybrids—together, they could move us faster toward a decarbonized transportation system,” Jayawardana says.
See also: 5 Technologies Steering Transportation Toward a Greener Future
Real-world applications are already underway. Google’s Project Green Light uses AI to optimize signal timing in multiple cities, benefiting up to 30 million car rides per month. The findings show that this isn’t just theory—eco-driving works outside of simulations.
The timing of the research is significant. Semi-autonomous and autonomous vehicles are becoming more common, which could allow eco-driving guidance to be automated in the near future. Drivers might not even need to open an app; vehicles themselves could adjust speeds to reduce emissions while keeping traffic flowing.
Nationally, widespread adoption could have a major impact. MIT estimates that eco-driving could save as much annual emissions as the total yearly output of Israel on the low end, or Nigeria on the high end. These are country-level reductions achieved with a simple, accessible technology.
Eco-driving also complements other climate-friendly measures. Electric and hybrid vehicles benefit even more when intersection driving is optimized, showing that reducing the traffic light climate impact strengthens, rather than competes with, electrification efforts.
The study, published in Transportation Research Part C: Emerging Technologies, is the first city-scale analysis of the traffic light climate impact. Previous studies were too small to offer actionable insights for policymakers. Now cities have data to plan eco-driving campaigns that deliver measurable reductions.
The research highlights a broader principle: Small, systemic improvements in everyday infrastructure can produce meaningful climate results. Traffic lights aren’t just a commuter frustration—they’re an opportunity to cut emissions while improving fuel efficiency and air quality.
Ultimately, the power of eco-driving lies in its accessibility. With just a smartphone, drivers can help reduce citywide emissions. It’s a democratic, low-cost, and practical intervention in the fight against climate change.
