Delhi’s Odd-Even plan had a significant effect on pollution

Researchers Michael Greenstone, Santosh Harish and Anant Sudarshan have some news for us. Hard data that shows that the Odd-Even plan reduced pollution by significant levels in Delhi. The headline: this study finds there was an 18% reduction in PM 2.5 due to the pilot during the hours that the rule was in effect. The effect size is truly staggering, and is quite unusual for studies that use such rigorous methodology to look at the impact of policy interventions.

Starting January 1, while absolute pollution levels increased both inside and outside Delhi (for atmospheric reasons, as noted by other commentators), the increase in fine particle levels in Delhi was significantly less than in the surrounding region. Overall, there was a 10-13 per cent relative decline in Delhi.

…Around 8 am, the gap between Delhi’s pollution and that in neighbouring regions begins to form and steadily increases until mid afternoon. As temperatures begin to fall, and pollution is less likely to disperse, this gap starts to close. We see another small gap emerge between 9-11 pm, which probably reflects the new limits on truck traffic in Delhi, which also came into force on January 1. Soon after midnight, the gap closes, and Delhi and neighbouring areas show similar pollution patterns until 8 am comes around again. When focusing just on the hours that the odd-even policy was in effect, our estimates suggest that particulates pollution declined by 18 per cent due to the pilot. 

As I said in my previous post, this pilot set a great template for citizen engagement with a public policy reform experiment: heightened awareness regarding the core issue, mass participation, intense public scrutiny, and a data-driven discourse. While debates have raged over the success of this scheme, the last piece – hard data – has now come in. It should be welcomed, and analysed further.

The methodology and analysis is set out in greater detail here:

We compare the changes in PM2.5 concentration levels before and after the program in Delhi monitors and outside Delhi in the NCR: Faridabad, Gurgaon and Noida .While the odd-even program was in place for commuters from these cities to Delhi, the odd-even program was not directly implemented there. If anything, the impact on the commuters makes our estimates lower bounds to the true impact.

In doing this, they addressed a glaring oversight that journalists were earlier making – of taking into account, what would have happened in the absence of this pilot and comparing that with Delhi. Using a counterfactual and a difference-in-difference approach, the researchers are able to conclude that the levels of pollution in Delhi were indeed lower during the fortnight that the Odd-Even plan was implemented.

What one needs to consider is also whether this arrangement is sustainable in the long-term? Perhaps not, as has been the experience in other cities, unless Delhi sees collective action at an unprecedented level (phasing out old cars, people agreeing not to buy second-hand cars, etc). But while you cannot change the weather, and it may be difficult to stop farmers from burning crop waste in the short-term, the success of Odd-Even presents a new and effective tool – an option that can be implemented to bring down peak air pollution, or neutralise at times when the weather is most unfavourable.

The Delhi government should remember though that without serious efforts to expand and improve public transport, and introducing measures such as congestion pricing, or other forms of pollution taxes, vehicular pollution will not be controlled. Governments or leaders who claim to have all the answers probably aren’t the ones who would be open to trial and learning. As the researchers say:

More generally speaking, governments need to accept that we don’t have all the answers to policy problems and adopt a culture of trying out new ideas, testing them carefully, and then deciding which ones to adopt at scale

So the biggest gain from the Odd-Even plan would be a willingness to participate in experiments in collective action – a citizenry that is aware, engaged, and willing to work together with its government to find solutions to its problems. Here’s hoping we see many more of such ideas…and in the meantime, the Delhi government deserves a wide round of applause.

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