The city of about 20 million, which ranks among the world’s top cities with foul air on a WHO list, has almost 10 million vehicles, a record it set this year.

Delhi government data released on Thursday shows the number of registered vehicles increased from 8.8 million in 2014-15 to 9.7 million in 2015-16 — a spike of 9.93% and the highest in eight years.

The city has the country’s highest density of vehicles, a primary source of air pollution.

According to an IIT-Kanpur report, toxic exhaust fumes from vehicles constitute 25% of the city’s air pollution. The latest government data show 6,502 people died of respiratory diseases in 2015, making it one of the leading causes of death.

Exhaust fumes coupled with smoke from farmers burning paddy stalk in neighbouring states and dust from construction sites formed the thickest smog for two decades to shroud the city after Diwali this year.

The Capital is struggling to reduce its air pollution, with measures such as a road rationing formula that allows cars with odd- and even-numbered number plates to ply on alternates days. The government as well as the National Green Tribunal and pollution control boards had banished smoke-belching trucks from the city and sought to scrap all ageing vehicles above 15 years.

But these measures are having little effect as people are forced to arrange their own ride because of an inadequate public transport system, which runs mainly on clean fuel such as CNG and electricity.

The ridership and fleet strength of the Delhi Transport Corporation — the city’s public transporter — depleted in the past year. From almost 3.9 million in 2014-15, the daily average ridership of DTC buses decreased to about 3.5 million in 2015-16, the data show.

The number of buses depleted from 4,705 to 4,352 during the period, despite the government’s efforts to bulk up the fleet to encourage people to use public transport more often to reduce air pollution.

The city needs 11,000 buses but even with private buses bolstering the operation, it is around 4,000 short.

Besides pushing air pollution up, the rise in vehicle density has clogged the city’s road network and forced Delhi residents to spend more time travelling. A study by six road design experts found recently that people’s commuting time has doubled in the past six years and traffic speed has halved during peak hours.

The average speed has come down from 42kmph to 20kmph. Experts said the city will crawl at 5kmph in 10 years, the average speed at which a human walks.

The data released by deputy chief minister Manish Sisodia also inform that city’s per capita income stood at Rs 280,142 during 2015-16; it has more mobile and fixed line phones; and power consumption has come down to 24,037 million units.