In 2015, our team at the International Council on Clean Transportation uncovered what would become one of the automotive industry’s most expensive and transformative scandals. Testing three diesel cars on regular streets and highways outside the standardized lab testing, we discovered that NO_x emissions from Volkswagens’ diesel Jetta and Passat models sold in the United States were up to 35 times higher than legal limits. This scandal would cost Volkswagen over $34 billion in fines, penalties, and settlements and it spurred governments in most major auto markets to dramatically improve compliance and enforcement programs and policies.  A decade later, we’ve made remarkable progress. But there’s still much more to do to address elevated levels of air pollution and greenhouse gas emissions from on-road vehicles.  

Dieselgate revealed major weaknesses in compliance programs worldwide that lacked effective mechanisms to ensure on-road vehicles maintained low emissions throughout vehicle lifetimes. In the United States, real-world testing exposed software that detected when a vehicle was tested under laboratory conditions. These illegal “defeat devices” switched emission control systems on when undergoing official tests and then disabled or reduced the effectiveness of emission controls under normal driving.  

In the wake of Dieselgate in the United States, EPA announced a real-world emission testing program. In addition, $2 billion in Volkswagen’s penalties was allocated to build out EV charging infrastructure while nearly $3 billion flowed to U.S. states to fund projects to reduce diesel emissions. 

While largely limited to Volkswagen in the United States, subsequent testing by Germany, France, and the UK revealed widespread use of similar software across many models of diesel cars sold in Europe, although at the time such practices were not considered illegal. However, these revelations about elevated real-world emissions led the European Commission to establish a new framework for on-road testing including a new real world driving program that more accurately reflected normal driving conditions. This program went into effect for all new passenger cars sold in Europe in 2019 and has been adopted in various forms by many countries including India, China, Korea, and Japan.  

Dieselgate continues to drive transformative changes across the industry and regulatory landscape, including a ruling by the European Court of Justice in 2022 clarifying what constitutes an illegal defeat device in Europe. Improved compliance programs have reduced air pollution and supported the adoption of CO₂, greenhouse gas, and fuel economy standards. Together, these changes have accelerated the transition to electric vehicles (EVs). Through international pledges like the Zero Emission Vehicles Declaration signed by more than 100 countries, businesses, and organizations, there is a global movement to shift towards zero-emission passenger cars in major markets by 2035. As a result of pressure from cities banning diesel cars  and European CO₂ standards, Europe’s diesel car market share dropped from 52% in 2015 when Dieselgate broke to 18% in 2023. Meanwhile, the European EV market share surged to 25% in 2025.    

Despite this significant progress, tens of millions of high-emitting diesel vehicles remain on roads worldwide. The TRUE Initiative, which was founded on the heels of Dieselgate to serve as an independent source of real-world emissions data, reveals that even diesel vehicles certified to world-class emission standards still sometimes emit 2 to 4 times the allowable limits of NO_x. We continue to see excess emissions from both older vehicles and some newer models. 

The health impacts are alarming. Without further policy action, annual road transport-attributable premature deaths are projected to surge from 193,000 globally in 2023 to nearly 278,000 by 2040, with children facing continued risks of asthma from vehicle pollution. Yet comprehensive policies could prevent this escalating crisis—saving 1.9 million lives and preventing 1.4 million children from developing asthma in the same time period. In the U.S. alone, such policies could save 31,700 lives and prevent 87,100 new asthma cases. 

Accelerating the shift to electric vehicles represents one of our most powerful solutions —a technological breakthrough compared to incremental emissions improvements from internal combustion vehicles. A relatively underappreciated benefit of battery electric vehicles is that there is no need for extensive and expensive compliance and enforcement programs since EV are inherently clean.  

Over the last several years, the economic case has substantially improved with small battery electric cars in China selling for half the price of a comparable gasoline vehicle. The result of EVs reaching, or coming close to, purchase price cost parity with petrol vehicles is that EVs make up more than 50% of vehicles sold in China, more than a quarter sold in Europe, and are reaching double-digit market shares in emerging markets such as Thailand, Vietnam, Indonesia, and Australia. Even Toyota, not the most enthusiastic adopter of EV technology among legacy automakers, has introduced a best selling electric SUV into the Chinese market.  

Ten years after Dieselgate, progress has been impressive but challenges remain. On the positive side, all the world’s major vehicle markets have dramatically upgraded their compliance and enforcement programs for on-road vehicles. Further, the transition to electric vehicles is well underway for passenger cars and transit buses with some lag time for heavy-duty trucks. On the downside, we have not fully solved the problem of excess emissions for vehicles under normal driving conditions. As a consequence, people living in major urban areas around the world continue to breathe unhealthy air with significant contributions from the transport sector. We’re also witnessing a wholesale retrenchment of environmental policy in the United States. Overall, the last decade has witnessed impressive progress towards clean vehicles and fuels, and we look forward to even greater progress over the next ten years!