Mexico City Launches Its Boldest Attack Yet on Smog : Pollution: Drivers must leave their cars immobile one day a week. If they don’t, they face penalties.

With the seasonal morning haze evolving into now-familiar brownish photochemical soup, authorities here this week launched their strongest action to date in battling Mexico City’s infamous smog.

Between now and Feb. 28, when spring winds begin to disperse the ubiquitous airborne pollution that is fiercest during the winter months, motorists here are required to leave their cars immobile for one day each week between 5 a.m. and 10 p.m. Monday through Friday.

Drivers who are identified via a color-coded registration sticker system face fines equivalent to about $115, the highest ever for motor violations here. Their vehicles are also impounded for at least 24 hours.

The so-called “Day Without a Car” campaign seeks to remove more than 400,000 vehicles from the capital’s congested streets each day, reducing noxious emissions into the air by perhaps 2,000 tons daily.

The much-ballyhooed and long-awaited initiative is a key part of a broader crackdown that involves a range of measures, including required installation of catalytic converters in new automobiles; the introduction of cleaner, faster-burning gasoline, and the long-delayed imposition this month of mandatory emissions inspections.

Taken together, the efforts indicate that, after years of foot-dragging, Mexican authorities have finally recognized that Mexico City, the world’s most populous metropolis with about 20 million residents, represents a potential environmental calamity. Already, a series of studies have linked the sooty air to a range of ailments, from high levels of toxic lead in the blood of the young to respiratory problems in the older population.

“This is really the first positive measure that the government has taken to reduce pollution in Mexico City after many years of lip service,” said a spokeswoman for the Group of 100, an environmental organization here that first proposed vehicular restrictions for the capital almost five years ago.

Nonetheless, the effort is limited. For instance, buses, which contribute mightily to the befouled atmosphere, are exempt from both the one-day “no-drive” campaign and from emission-test requirements. The emission-testing program, meantime, has been marred by fraud and payoffs to officials, critics say.

In order to enforce such a massive regulatory undertaking as the “no drive” effort--there are about 2.3 million registered vehicles in the metropolitan area--authorities last year began devising a color-code system for registering vehicles. Registration stickers, prominently displayed in rear windshields, now display one of five colors; each “no drive” day is tied to a certain color sticker.

On Tuesdays, for example, vehicles displaying pink stickers are not allowed to circulate.

The program--based on similar efforts in cities as diverse as Singapore, Athens and Santiago, Chile--began Monday amid considerable doubt that the district’s police would actually enforce the law. Many feared that officers would instead resort to common practice: accepting bribes and allowing motorists to pass.

However, officials here teamed police with city inspectors at 45 key intersections throughout the city, in part seeking to cut down on the solicitation of bribes by police officers working alone or in pairs.

In addition, authorities reasoned that the strict enforcement would reduce the propensity of motorists to offer bribes. “If someone is stopped five or six times, I don’t think they’re going to keep paying,” noted Ramon Ojeda Mestre, director of pollution prevention and control for the municipal government here.

Based on the first few days, officials here pronounced the program a success. On Monday, the first day of the program, Ojeda said, about 2,000 cars were impounded and their owners fined.

In fact, experienced drivers downtown did notice some easing of the traffic that makes driving here such a frustrating experience. “There seems to be the same number of cars, but the traffic is a bit more fluid,” noted Gustavo Jasso, a taxi driver.

As expected, there were widespread complaints from motorists suddenly unable to drive their vehicles. Commuters complained that promised increases in bus and other public transportation services were not forthcoming. Residents of poor outlying communities protested that the program favors the wealthy, who can afford to own multiple vehicles. Businessmen sought exceptions for their concerns, mostly without success.

“I’ve had calls from Coca-Cola, Pepsi-Cola, the beer distributors; everyone wants an exemption,” Ojeda, the government anti-pollution official, said during an interview at his office.

Exemptions, officials said, are being granted only for taxis, buses, other public transport vehicles and in certain other cases, such as for trucks transporting perishable food, for medical vehicles and for the handicapped.

“If the president drives by and his car shouldn’t be on the road, we’ll take it off the road,” vowed Juan Alvarez Davalos, a city inspector posted on the well-traveled intersection of Florencia and Chapultepec avenues.

Nearby motorists waiting for their cars to be led to the impound lot seemed resigned, although all complained that authorities could have done more to inform the public about the details of the campaign. There has been considerable confusion, despite a broad publicity effort involving posters, television and radio spots.

“I have no problem with the idea; we have to get vehicles off the road or none of us will be able to breathe,” said Benito Perez, a 24-year-old delivery truck driver for an import firm. “I just wish they had told us more about the requirements.”

Added another city resident: “If we don’t do something soon, we’ll all die like flies sprayed by insecticide.”