Delhi’s air pollution often dominates global headlines, and vehicles are one of its largest contributors. To control these emissions, India relies on the Pollution Under Control (PUC) certification system, which requires vehicles to regularly undergo emissions testing. But how reliable are these tests in practice? Concerns about testing quality and irregular practices at some centres raise an important question of high-emitting vehicles slipping through the cracks.
In collaboration with the Transport Department, Government of NCT of Delhi, researchers at the Energy Policy Institute, which is a key research unit within the University of Chicago’s Institute for Climate and Sustainable Growth, are studying whether stronger supervision at testing centres can improve the integrity of emissions testing. The central research question here is: Does increased oversight influence how PUC tests are conducted and improve the detection of vehicles that do not meet emissions standards? The study also seeks to understand how malpractice may occur and how testing practices change when operators know they are being observed.
To answer these questions, the research team designed a randomized controlled trial focusing on PUC centres across Delhi. Among centres conducting at least 300 tests per month, 90 were randomly selected from a pool of approximately 450 centres in the city. The study was conducted over one month beginning in late June 2025 and continuing through July, introducing randomized supervision visits to examine whether oversight changes testing outcomes.
Anant Sudarshan, Senior Fellow at EPIC; Associate Professor in the Department of Economics at the University of Warwick, and one of the principal investigators of the study, states, “Vehicle emissions testing is one of the most important tools cities have to control pollution from the transport sector, but it only works if the testing process itself is credible. Our goal with this study is to understand where the system may be breaking down in practice and to uncover the specific ways testing outcomes can be manipulated. Evidence from this research can help policymakers design stronger monitoring systems that ensure high-polluting vehicles are accurately identified.”
While conducting unannounced visits to a rotating sample of PUC centres, each location had an equal chance of being observed across different days and time slots. During these visits, they monitored testing practices, assessed whether standard procedures were followed, such as proper placement of emissions measurement equipment, and recorded any irregularities. They also noted vehicle registration details, which were later cross-checked against entries in the central PUC database to identify discrepancies between tests conducted at centres and those officially recorded.
Jeanne Sorin, Postdoctoral Scholar at University of Chicago’s Institute for Climate and Sustainable Growth, and co-principal investigators in the study added, “By introducing randomised supervision, we were able to observe how testing outcomes shift when centres are monitored more closely. The results suggest that emissions may be systematically underreported in routine conditions, raising important questions about the reliability of the current system and the need for stronger oversight mechanisms.”
Preliminary findings from the study highlight that emissions readings recorded during supervised tests were significantly higher on average than those recorded when centres were not supervised. Carbon monoxide and hydrocarbon readings both increased under supervision, suggesting that tests were conducted more accurately when operators were observed. The probability of a vehicle failing the emissions test also increased substantially. Administrative data further suggests that some tests that fail may not always appear in the official database.
Together, the findings suggested that the current system may underreport the true number of high-emitting vehicles on the road and that even limited, targeted supervision can significantly improve compliance with testing procedures.
Early findings indicate that improving oversight can significantly enhance the accuracy of emissions testing, but this is only the beginning. Ongoing analysis is exploring how these insights can be translated into scalable, evidence-based policy solutions to further strengthen Delhi’s vehicle emissions control system. Through its partnership with the Delhi Transport Department, this research will contribute to ongoing efforts to strengthen regulatory systems that identify high-polluting vehicles and support cleaner urban air.