The Energy and Resources Institute (TERI) which released an impact assessment study on the two-phases of odd-even scheme observed that as private cars have limited contribution in the PM2.5 levels, the scheme yielded only "marginal" reductions (4-7 per cent) during both the phases.
TERI observed that the impact of the scheme with respect to traffic counts, average speeds and air quality declined during the second phase in comparison to the first phase and the decline could be probably due to people opting for "second cars with alternative number plates, installations of CNG kits or enhanced use of taxis".
"A more sustainable approach for dealing with air pollution not only in Delhi but also in other metropolises would be congestion pricing, which is a far more effective option," Director General of TERI Ajay Mathur said.
Congestion pricing is based on a 'pay-as-you-use' principle with an aim to reduce the number of vehicles and in turn encourage modal shift by charging vehicles on entry in restricted zones and times. This can be complemented by providing exemptions to higher-occupancy vehicles.
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The congestion pricing scheme can be first tried out in different ways including, all across congestion pricing, identification of low-emission zones and road-wise congestion pricing, TERI said.
Sumit Sharma, fellow at TERI, said that the measures,
which were taken, were more to control particulate matter rather than Oxides of Nitrogen (NOx). "We need multi-sectoral measures for the whole NCR to effectively reduce air pollutant levels, which calls for regular air quality management plans based on scientific studies," he said.
The body said that during phase II of the scheme, the general variation of PM 2.5 concentration due to daily changes in local emissions, meteorology and background concentrations (influences from outside Delhi) was 42 per cent.
The reduction achieved from the scheme during this phase seems too small (4 per cent) to be captured among the other more dominating factors.
"This is likely to happen as the public transportation system is not reliable and attractive enough to encourage the car users to shift to public transport.
"Hence, the odd-even scheme should be used only as an emergency measure when the pollution levels are expected to be very high like winters. Regularizing it or its frequent use may only reduce its impacts, unless public transportation is improved and sales of alternative vehicles are checked," it said.
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Elaborating on the congestion pricing, TERI said the equity concern of the principle may be taken care of by carefully setting up the congestion charges and earmarking the revenues from congestion pricing for providing mass transport options in these zones as a public responsibility.
It said that car users in general are much richer than the non-car users and should pay for the additional pollution caused due to their cars.
"It is expected that through congestion pricing, public transport will improve and attract more people as there will be a clear discouragement to use private vehicles. Contrary to the Odd-even scheme, the congestion pricing scheme can work throughout the year and provide year-long benefits of lower congestion and pollution levels and savings on fuel," TERI said.
It said that during phase-I (January, 2016), there was an increase of 25 per cent, 22 percent, and 27 per cent in PM2.5, PM10, and NOx concentrations respectively while in phase-II, the increase was 39 per cent, 26 per cent and 25 per cent, respectively.
"Odd-Even-II led to a reduction of 4 per cent in 24-hourly PM2.5 concentrations, largely because of the fewer number of cars on road. In other words, the concentrations could have been 4 per cent higher than those observed in absence of the scheme.
"The 4 per cent decrease in PM2.5 attributable to a 17 per cent decrease in car numbers is because the lower number of cars on the roads also reduce idling emissions from other category of vehicles (2-wheelers and buses) and reduce the amount of road dust," it said.
It said that industrial emission trading schemes and fiscal measures should be explored while standards for NOx and other important pollutants for industrial establishments should be put in place apart from ensuring 24x7 power supply in NCR to curb the use of Diesel generator.