The Delhi government may miss the pollution reduction targets it aims to achieve by implementing the odd-even vehicle policy by a significant margin, as exemption for two-wheelers may play spoilsport for the new rule to be successful, according to experts.

Two-wheelers account for nearly 33% of particulate matter (PM) emissions in the transport sector, next only to trucks, a recent draft IIT Kanpur report showed.

Out of the total 89 lakh registered vehicles in Delhi, two-wheelers are 51 lakh, and any policy aimed at controlling pollution should include two-wheelers, experts said.

"If this segment is left out and a sizeable number of cars are also allowed because of the exemption granted to single women drivers, the overall effectiveness of the programme will be compromised. It cannot act as an emergency measure to bring down peak pollution levels. The Centre for Science and Environment (CSE) would urge the government to bring two-wheelers within the mandate of this programme," The Economic Times quoteed Anumita Roychowdhury, head of CSE's clean air programme, as saying.

Even though motorcycles or scooters and bikes occupy less space and are fuel efficient, one two-wheeler is estimated to "emit almost as much as a BS-III standard car."

According to an analysis by the International Council on Clean Transportation (ICCT), two-wheeler emissions include particulate matter (PM), carbon monoxide (CO), nitrogen oxides (NOx), hydrocarbons (HC) and sulphur oxides (SOx), and the emissions vary depending on the sulphur content in the fuel.

"The chemical nature of PM emissions from bikes is very different from that of diesel, which is why bikes are considered a lesser evil," CSE researchers said.

IIT Kanpur's draft study also showed that diesel vehicles accounted for 60-90% of PM 2.5 emissions in some parts of the national capital.