The court also barred all diesel vehicles, whether light or heavy, that are older than 10 years from plying on roads in major cities like Thiruvananthapuram, Kollam, Kochi, Thrissur, Kozhikode and Kannur.

“Upon expiry of 30 days from today, if any vehicle is found violating this direction, then it will be liable to pay Rs.5,000 per violation, as per environmental compensation,” the court said.

Strangely, the order does not take into account the fact that a buyer makes an upfront payment of road tax for at least 15 years when purchasing a new car.

However, it exempts vehicles used for public transport and local authorities from the ban.

Kerala is the second largest market for passenger vehicles in southern India, accounting for 7% of the total passenger vehicle sales in the country.

Karnataka is the largest market in the region with a 7.5% share of passenger vehicles sold annually.

These interventions are aimed at reducing vehicular pollution.

As per a World Health Organization (WHO) report released on 13 May, smaller cities are registering much higher levels of air pollution.

For example, in Allahabad, PM2.5 levels have almost doubled in the last two years. At 18th place in 2014, it had a PM2.5 level of 88 ug/m3 (micrograms per cu. m). In 2016, its PM2.5 has increased to 170 ug/m3.

Cities such as Ludhiana, Kanpur and Agra also show a substantial increase in PM2.5 levels.

Particulate matter (PM) is associated with adverse health effects. The smaller the particles, the deeper they penetrate into the lungs and the cardiovascular system.

They can cause strokes, heart disease, lung cancer and chronic and acute respiratory diseases, including asthma.

AnumitaRoychowdhury, executive director of the Centre for Science and Environment (CSE), a Delhi-based environment think tank, said that the green tribunal’s order is a “pointer towards the fact that India as a country now needs a restrained policy on dieselization; otherwise, city by city, action will begin”.

“We cannot address the health risks with current diesel technology. So, we should leapfrog very quickly to cleaner technology; but till that time, we should restrain this in whatever way,” she added.

Vishnu Mathur, director-general, Society of Indian Automobile Manufacturers, or Siam, could not be reached for comments.

However, a top executive at a car company said the order was an example of “excessive judicial activism”.

“Laws are defined by the legislature and executed by executive. These days, judicial activism has taken over those functions,” the executive said, requesting anonymity.

On 18 May, Mint reported that car makers fear a wider impact of the Supreme Court’s diesel ban for the national capital region.

“Tomorrow, it will affect Mumbai and other metro cities, such as Kolkata, and then it will come down from 2,000cc to may be 1,000cc or 800cc,” Y.K. Koo, managing director at Hyundai Motor India Ltd told Mint.

While it is not clear whether such actions will be enough to fix the air quality in cities, the measures are a setback for the automobile industry, whose sales have only just begun to pick up.

Rating agency Icra Ltd in a report on Monday said that the government’s decision to leapfrog to BS VI emission norms by 2020 will push up vehicle prices in the country.

It estimated the cost of petrol passenger vehicles to increase by Rs.20,000 to Rs.30,000 per vehicle, and diesel passenger vehicles by Rs.75,000-Rs.1 lakh per vehicle. For medium and heavy commercial vehicles, the cost differential is expected to be up to Rs.1.5 lakh or 10% of current vehicle cost.