On Dec. 18, 2000, the city of Bogotá introduced a new bus system that it hoped would speed transit, ease gridlock and cut smog in one of Latin America’s most chaotic and contaminated cities.

The system, TransMilenio, has in many respects proved a big success. For about US$500 million—less than 10% of the cost of the Washington, D.C. Metro—the Colombian capital provided reliable public transportation to a large share of its population.

Featuring articulated buses running in dedicated lanes at an average 26 kilometers an hour—just two kilometers an hour slower than the Washington Metro—TransMilenio now serves 670,000 passengers a day, meeting 20% of Bogotá’s commuter demand. And with a ticket price the poor can afford, the system has won accolades from riders, more than 85% of whom consistently express approval for it in polls.

Overshadowing TransMilenio’s successes, however, is an uncomfortable fact—Bogotá’s air pollution and gridlock remain severe.

A key cause of this problem, city officials say, is an excess of some 8,000 privately owned buses serving non-TransMilenio routes. Though these private, city-approved buses serve as an important income source for their blue-collar owners, they clog thoroughfares and contribute to protracted traveling times.

Meanwhile, air pollution continues to saddle Bogotá with among the highest rates of respiratory disease in Latin America. In 2004, some 220 children aged five or younger died of asthma, bronchitis or other types of respiratory ailments. Doctors say a large percentage of those cases were exacerbated, if not directly caused, by diesel pollution from buses.

“TransMilenio is a magnificent transportation system that can move more people per hour than most metro systems in the world,” says Arturo Ardila, an engineer who recently completed a doctoral dissertation on TransMilenio at the Massachusetts Institute of Technology. “But the oversupply of non-TransMilenio buses that run on poor-quality diesel results in terrible problems of congestion and contamination.”

Phase-out fizzled

It was not supposed to be this way. Enrique Peñalosa, a U.S.-educated urban planner who served as Bogotá’s mayor from 1998 to 2000 and conceived TransMilenio, imagined the new transit system replacing much of the privately owned fleet of legal but decrepit buses, many of which are two decades old. Antanas Mockus, who replaced Peñalosa in office during 2001-04, even ordered cash payments to purchase and junk 4,000 old buses.

But lawsuits from the owner-operators of non-TransMilenio buses and pressure from politicians supporting them foiled Mockus’s effort to make the bus removals permanent. Indeed, most bus owners used the cash they received from City Hall to buy new vehicles, leading to a net reduction of only 250 buses during his three years in the mayor’s office.

Meanwhile, foot-dragging by the national government defeated the mayors’ hope of making Bogotá a substantially cleaner place. Colombia produces some of the Americas’ filthiest diesel, with a sulfur content of 4,000 parts per million, compared to 15 parts per million in California and 500 parts per million in Chile.

Bogotá has a special allotment of cleaner fuel containing 1,500 parts of sulfur per million, which still is dirtier than that of virtually every Latin American city outside Haiti.

Despite decades of discussion, it was only recently that Ecopetrol, Colombia’s state-owned oil company, committed to invest a total of US$1.1 billion at two refineries to increase capacity and improve the quality of diesel so the fuel attains a national standard of 300 parts sulfur per million in 2008.

Air-quality experts say that in the meantime, sulfur contamination will likely remain a serious problem here. High sulfur content in diesel, in addition to reducing visibility by contributing to smog, produces particulates that contain carbon, hydrated sulfates and other elements that can help cause respiratory and cardiovascular disease.

Dirty diesel

Because it uses the same diesel, even TransMilenio is unable to alter the air-quality picture significantly. While the system’s buses are outfitted with equipment that meets the highest European environmental standards, these pollution-control devices don’t count for much when used in combination with high-sulfur diesel, experts say.

“TransMilenio has equipment that in normal circumstances would make it extremely clean,” says Eduardo Behrentz, an assistant professor of civil and environmental engineering at the University of the Andes in Bogotá. “But the regular buses, which would never pass muster in Europe, and TransMilenio use the same fuel and, as a result, the contamination is the same.”

Other experts add that though preliminary experiments are being made using compressed natural gas in TransMilenio buses, it is by no means clear that natural gas would provide sufficient power in Bogotá’s high altitude (2640 meters above sea level) conditions.

For now, the city appears resigned to merely treating the sick.

In late 2004, current mayor Luis Eduardo Garzón established a special committee of experts on respiratory disease and established 40 new clinics to treat children. As a result, physicians working for City Hall say they expect infant mortality from respiratory problems to drop around 20% when statistics for 2005 are tallied.

Though Garzón, a leftist politician who campaigned with the support of working-class bus owners, has opposed eliminating buses in the past, experts believe public-health concerns will force his administration to address the problem.

“Local doctors have recently become very aware of the overwhelming connection between old buses, diesel, and disease,” says Luis Hernández, an epidemiologist for the city. “They are beginning to lobby. I think City Hall will end up taking drastic measures.”