Delhi's Air Pollution: Impact of Odd-Even Policy

Most of our readers may have heard of the 'Odd-Even' currently being tested in Delhi by the state government. Per this rule, vehicles with odd registration numbers will be allowed to be on the road on odd dates and those with even ones on even dates. There are several exceptions to the rule including women drivers and public transport vehicles. The government tested this rule from January 1st through January 15, 2016 and again from April 16 through April 30, 2016. We obtained publicly available data to test how some of the city's neighborhoods fared during the test implementation phase of the rule and decided to analyze it. The findings were surprising to say the least.

In each of the 3 neighborhoods we looked at- RK Puram, Punjab Bagh, and Anad Vihar, pollution was worse during the Odd-Even Test phase! You can toggle between neighborhoods in the chart by checking the box next to the neighborhood name. Green represents period of regular traffic and red represents Odd-Even testing period. First lets look at RK Puram. The Average level of 10 Micron Particulate Pollution during the April test phase was 340 and that during a similar period before the test was 256. In Punjab Bagh, it was 445 during the January test phase versus 440 in the latter half of January immediately after the test phase. In Anand Vihar 564 during the test phase and 507 immediately after. To be fair we did not do a rigorous Hypothesis Test to evaluate whether the differences between the 2 averages are statistically significant. However, this much is clear- at best, the Odd-Even policy had not effect on air pollution in Delhi, at worst, it made the problem worse than before! A quick reminder for our readers- safe levels of PM10 pollution are below 50.

So what might be going on here? We have a couple of theories although our readers are welcome to provide their own and pick apart the analysis as well. First, in order to accommodate the surge in travelers, the number and operating frequency of public transport vehicles on the road may have increased. These tend to be older, polluting vehicle which may have added to the pollution. Secondly, people may have resorted to using their older vehicles which they do not use as often, again adding to the pollution. Regardless of the outcome and the reasons behind it, it is important that the Delhi government examine variations of the approach. This is too important a health and public policy issue to be ignored and abandoned prematurely.

A brief background about the methodology: Although the data has data around different pollutants such as particulates, nitrogen oxides, and hydrocarbons, we looked at only the pollution due to particles less than 10 micrometer in diameter (PM10). We have an explanation of pollution indicators and pollution levels in major global cities from a previous Weekly Digest here. This is generally a good proxy for air pollution and simplifies the analysis approach. Lastly, we picked these 3 neighborhoods and the appropriate January and April timeframes since data for these was comprehensive. The daily pollution levels are actually an average of almost 24 data points- 1 for each hour of the day.