A police officer pulls over a traffic violator in Beijing recently.[Photo/China Daily]

When they become available, smog-hit Beijing might like to review them. Beijing and New Delhi, besides being national capitals, are comparable in terms of population (22 million and 16 million) and the number of motor vehicles (9 million and 7.5 million).

One-third of Delhi's 3 million cars were off the roads during the trial. Cars with license plates ending in an even number were allowed on even dates, and cars with odd-number plates on odd dates. Vehicles of the emergency services, security and police forces, VIPs, single women and cab services were exempted.

Media reports suggested that, during the trial, hazardous PM2.5 particulates hovered between "very poor" and "severe", well above the World Health Organization-prescribed safe limit. But Delhi claimed pollution eased and the roads were decongested.

Delhi will first study the results of the trial before deciding on its extension. But some media reports suggested a second trial may be conducted any time between March and June, once concerns related to school children's commuting and people buying a second car (like Beijingers did before the 2008Olympics) to circumvent the curbs are addressed.

During the recent Beijing car bans, 112,800 100-yuan ($15) tickets were issued for violations in just four days. In Delhi, offenders were fined 2,000 rupees ($30) each day, earning the local government 4 million rupees by Jan 5. Car owners, it seems, are happy to pay up and get on with life.

Alongside Beijing and Delhi, smog-hit cities in Italy are also restricting car use. But not everyone is applauding. For, just like excessive pollution, strong measures to combat it could entail economic consequences, logistics challenges, popular resentment, even ridicule (Delhi's trial sparked several jokes online).

Carmakers worry any long-term curbs on private cars could hurt an incipient sales recovery. Every day, an average of 1,400 new cars roll on to Delhi's roads.

"Let's not convince ourselves wrongly that a simple odd-even policy will solve the over-all air pollution issue," Arunabha Ghosh, head of the New Delhi-based Council on Energy, Environment and Water, told Agence France-Presse during the trial.

AFP also spoke to Pankaj Mehta, a Delhi resident who drives 45 kilometers to work daily but was forced to adopt a new commute drill. "Rickshaw (three-wheeler taxi), then metro (subway), then feeder bus, then walk, back and forth. A travel nightmare."

Others complained they had to call several cab providers as there were not enough taxis. They reported late for work, canceled scheduled meetings, and complained that their lifestyle was changed thoughtlessly.

To be fair, the Delhi trial saw some 80,000 gasoline or diesel cars converting to clean compressed natural gas, 6.4 million people riding city buses and more using the subway, which is expected to lead to their expansion and modernization.

Yet, given a choice, most car owners, be it in Delhi, Beijing or Rome, would likely prefer their own vehicles to public transport. What then could be a mutually acceptable trade-off for clean air?

How about a new tax on polluting cars, including taxis? Encourage owners of gasoline or diesel vehicles to upgrade to green ones. Until they do, use the tax proceeds to produce long-term solutions to air pollution.

Measures like a pollution tax, driving license auctions and higher parking fees may not be the best or universally acceptable solutions. But bans and fines could spark resentment and jeopardize economic activity.

For instance, civil defense volunteers who implemented the Delhi car ban had to endure abuse, petty altercations and even assaults. An auto industry crisis could erupt due to car bans, during which drops will likely affect employee productivity (due to commute-related stress and delays), fuel sales (down 30 percent in Delhi during the trial), consumer sales (no time for shopping, picnics, weekend getaways) and sales tax revenue.

But vehicles are not the only culprits. In Beijing, coal-burning power plants also pollute. Nearby hills exacerbate the problem by acting as a natural windbreak. Delhi's air is filthy because nearby agricultural fields burn farm waste, massive construction projects produce dust, the western Thar desert spews pollutants, and weather and seasonal changes wreak havoc.

Until cities have adequate public transport and efficient last-mile connectivity, tax, not odd-even bans, might be a preferable solution.