Regarding Pakistan,
NationMaster says 8 vehicles per 100 people - 112nd out of 134 nations. That's a fleet of 14,099,436 for their population of 176,242,949. If the US had a comparable percentage of cars it would be 24,324,778 total.
Clean burning NG?
BBC NEWS | South Asia | Pakistan 'faces pollution crisis'$this->bbcode_second_pass_quote('', 'T')raffic woes
The survey, released by the government's principal economic adviser, lists an increase in the demand for energy and an unprecedented growth in the number of vehicles in Pakistan as the key reasons behind growing levels of air pollution.
Air pollution levels in Pakistan's most populated cities are among the highest in the world, causing serious health issues in the process
Pakistan Economic Survey
The number of vehicles on the roads has increased five times in the past 20 years.
The biggest increase in the automobile sector is seen in two-stroke vehicles and diesel-powered goods lorries which are among the most polluting in the world.
Besides, more people are using cheap, inefficient and highly polluting fuels to meet their energy demands, the survey finds."In the cities, widespread use of low quality fuel, combined with a dramatic expansion in the number of vehicles on the roads, has led to significant air pollution problems," it says.
The government has been encouraging the use of vehicles powered by the less polluting compressed natural gas (CNG).
At present, CNG vehicles in Pakistan are estimated at just under one million, making Pakistan's CNG fleet the third largest in the world after Argentina and Brazil.
But lengthy bureaucratic procedures have impeded the growth of CNG filling stations, slowing down the expansion of the CNG fleet.
This story is a couple years old, btw. It illustrates that people will adopt whatever is economical first and foremost. Auto pollution hasn't gone away with the shift to NG:
$this->bbcode_second_pass_quote('', '')Nowhere in the world local governments spend money in widening roads,” said Rafay Alam, lawyer and member of LBT. He said: “Everyone in the world has woken up to the fact that automobile dependent cities are unsustainable.” Alam pointed out that Lahore had recently been recognised as being the most polluted City in Pakistan. He said that the government had allocated Rs 35 billion for education and health in the previous budget, but had allocated Rs 45 billion on the construction of roads and bridges.
When people get sick because of the air pollution, the reason they have no good hospitals or doctors to go to is because all the government’s money is being spent on the automobile elite.”