The fallacy of odds and evens
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In an effort to control high pollution levels in the city, the Delhi government recently ran a vehicle rationing scheme on a trial basis. The question is whether vehicle rationing is enough to reduce pollution substantially and whether other possible interventions by the government could be more effective.
As per the Delhi government plan, private vehicles with odd and even number plates were allowed on the roads on alternate days from Monday till Saturday every week from 1 to 15 January. Several categories of vehicles—such as two-wheelers, CNG (compressed natural gas) vehicles, cars driven by women, cars with handicapped people, cars registered to VIPs and commercial vehicles (autorickshaws and taxicabs)—were exempt from the scheme. Violators were slapped with a fine of Rs.2,000. Efforts were made to ensure adequate public mobility during the trial period. Six thousand additional buses were deployed and the Delhi Metro operated at a higher frequency. In addition, people were encouraged to carpool and 10,000 volunteers were hired across the city to help implement the scheme.
However, it is not clear if vehicular emissions is the major cause of air pollution in Delhi. A white paper by the ministry of environment and forests in 2003 mentioned that vehicles cause 72% of the air pollution in the city. However, this was contradicted by two later government studies. A Central Pollution Control Board study, conducted jointly with the National Environmental Engineering Research Institute in 2008, found that vehicles contributed only 6.6% to particulate matter emissions. According to this study, road dust was the biggest cause of pollution, accounting for more than half of Delhi’s particulate matter. A second government study conducted by the System of Air Quality Forecasting and Research reiterated the previous study’s findings and blamed road dust as the major cause of pollution.
A recent IIT Kanpur study again indicated road dust as the biggest contributor to the city’s PM10 levels (particles whose median diameter is less than 10 microns, air pollutants that are particularly harmful to human beings).
Even among sources of vehicular emissions, private cars are not seen as the biggest polluters. The Society of Indian Automobile Manufacturers estimates that vehicular emissions contribute to 20% of the air pollution in Delhi, and private cars, which are subject to the rationing policy, are responsible for only 2-4% of air pollution. Two-wheelers, which are exempt from rationing, are responsible for 30-40% of total vehicular emissions; trucks are responsible for another 30-40%. Moreover, three-wheel commercial autorickshaws generate more emissions than privately operated four-wheel cars.
Given the wide range of estimates of vehicular pollution and that various categories of vehicles have been exempted, it is very unlikely that the odd-even policy can significantly reduce pollution levels in the city. If two-wheelers and vehicles registered to VIPs are excluded, only 2.9 million of the 8.8 million registered vehicles in the city are subject to the policy as per the Delhi Statistical Handbook. Of these, 0.8 million cars are estimated to run on CNG. Further exemptions are provided to cars with female drivers, cars with handicapped persons, etc. If these exclusions are also factored in, approximately 2 million vehicles in Delhi are likely to be affected by the odd-even policy. Assuming the ratio of odd to even vehicles to be roughly equal, approximately 1 million vehicles will not be allowed on the streets on any given day of the policy. This represents 11% of the total number of vehicles in the city.
Studies on the odd-even policy in other cities have shown that vehicles that are on the road travel more, because they ferry more passengers through carpools and make more trips. For instance, Lucas Davis of Haas School of Business found that the number of private vehicles in a Mexican city actually increased under a similar rationing scheme, given the lack of quality public transport services.
Assuming that on-road vehicles drive 5% more than usual, the total vehicular distance travelled in Delhi can be estimated to decline by only 7%. If vehicular emissions are estimated to contribute roughly between 20% and 70% of Delhi’s air pollution, the odd-even scheme would reduce air pollution by 1% and 5%, approximately. Given that Delhi’s PM2.5 (fine particulates, which are even more carcinogenic than PM10 coarse particulates) are on average 15 times higher than the recommended World Health Organization (WHO) guidelines, the odd-even scheme will contribute very little to bringing down air pollution to desired levels.
Proponents of the scheme point to reduction in congestion leading to faster mobility as another benefit. But critics point out that restrictions on private vehicle movement, given the lack of an adequate and well-connected public transport, imposes a social cost on the owners of private vehicles.
Instead of rationing travel rights, cities like London, Singapore and Berlin cope with pollution control despite huge demand for mobility by having high-quality public transport systems. Apart from these, inter-modal connectivity and multi-modal integration enable smooth mobility and less reliance on privately owned vehicles for daily transit, as reported in the Planning Commission’s India Transport Report (2014). Congestion charging on a dynamic basis and higher parking charges have also been effective in increased patronage of public transportation in cities like London and Dubai. Social awareness of pollution and climate change can be promoted through the media. The government can help facilitate healthier and environment-friendly non-motorized transit choices by establishing dedicated cycling and walking lanes. Cleaner fuels can be encouraged to control transport-related emissions.
Lessons from experiences in other cities internationally suggest that vehicle rationing is at best an emergency pollution control mechanism. For long-term sustainability, multi-pronged policies based on scientific judgement and implemented diligently are much better at addressing the problem of air pollution.
Sundaravalli Narayanaswami is a faculty member in the Public Systems Group at IIM Ahmedabad. Quantitative approaches for urban mobility and intelligent transportation systems are her research interests. Arpit Shah is a doctoral student in the Public Systems Group at IIM Ahmedabad.