MEXICO CITY >> The future of Mexico City’s new airport, already about a third completed, comes down to a public vote this week in a political high-wire act by the president-elect that could shut down the country’s largest infrastructure project in recent memory.

After his election, Andres Manuel Lopez Obrador said Mexico’s people should decide the fate of the $13 billion airport designed in collaboration with celebrated architect Norman Foster. He had promised during his campaign to cancel it if elected.

Over four days beginning today, citizens will cast ballots on whether to continue with the new airport or update Mexico City’s existing one and another airport two hours away in Toluca, while building two new runways at a military base that would be converted to commercial use.

Supporters of the new airport say it is needed because Mexico City’s Benito Juarez International Airport handles more traffic than its designed capacity and a solution is urgently needed to satisfy growing demand.

Surrounded by residential neighborhoods, the old airport has no room to add new runways. And supporters point to a study by U.S. corporation Mitre saying that while the alternative plan is technically feasible, it presents important logistical problems and overall is unviable.

Opponents counter that not only is the new airport a potential sinkhole of corruption, but it is an environmental disaster, threatening a decades-old effort to restore the lakes that originally covered the valley in which the capital sits. Locals also say they were not consulted.

Lopez Obrador has said he wants to remain impartial, but he and his Cabinet picks consistently make the case against the new airport, characterizing it as too expensive and a windfall for corrupt interests.

Last week, he said the second option could save $5 billion. He hasn’t said, though, what will be done with the skeletal remains of new airport if it loses. About $6 billion has already been poured into the site northeast of Mexico City.

“Corruption is over, influence is over, impunity is over,” Lopez Obrador said in a recorded message this month. “We’re going to resolve this issue in the way that best suits Mexico, the national interest, and what the people decide.”

Ivonne Acuna Murillo, a professor in the political science department at Iberoamericana University in Mexico City, said Lopez Obrador has continually said he wants to govern with and for the people. He won 53 percent of the votes in July’s election and takes office Dec. 1.

“He understands very well where his strength lies,” she said.

Still, Acuna believes Lopez Obrador is playing a bit of a “cat and mouse” game trying to pressure Mexico’s business elite into footing the bill for the airport.

It could be working. On Tuesday, the current tourism minister, Enrique de la Madrid, said on a local radio show the new airport is such a good business that it could be paid for without public funds.

Lopez Obrador cast his own ballot today amid a mob of news cameras in the southern Mexico City borough of Tlalpan, at one of more than 1,000 voting stations in the capital.

At one station about a dozen people were in line at midmorning.

Cynthia Riverol, 65, said she voted for the airport to proceed.

“I believe that even though this referendum is not the wisest thing to do, because we’re missing a lot of technical information, we have a more-or-less educated opinion,” Riverol said. “And I believe that, financially and technically, the current construction must go on.”

The nationwide “consultation,” as the vote is being called, is not being conducted by the governmental National Electoral Institute. Lawmakers from Lopez Obrador’s Morena party have put up the money to hold it and volunteers are staffing the polling stations. The vote count will be conducted by the Arturo Rosenblueth Foundation, an academic institution.

On a recent morning, Lopez Obrador’s pick for transportation minister stood above an open pit mine as trucks dumped muddy sediment from the new airport site about 10 miles (16 kilometers) away.

Surrounded by residents of communities near the project, Javier Jimenez Espriu said he was gathering information and helping to inform citizens about the project and its impact.

His talk was interrupted by Felipe Alvarez Hernandez, a member of Peoples in Defense of the Earth Front, a group that has been fighting proposed airports in the area for nearly two decades.

“If the (vote) is going to say that it should continue, then you are violating our rights with the query,” Alvarez said, holding a machete aloft.

Jimenez asked the crowd what they wanted.

“That it’s canceled, that’s all,” Alvarez said.

A previous attempt to build a replacement airport in San Salvador Atenco in 2002 was canceled due to local opposition.

In San Nicolas Tlaminca, where Alvarez was talking, residents worry the mud being dumped is toxic and will contaminate their ground water. Residents of other nearby towns say the project requires so much basalt and another reddish volcanic rock that mines are altering their landscape.

At the site of the new airport, work continues full-steam ahead. The schedule calls for construction to wrap up toward the end of 2021.

The site was a hive of activity on a recent morning. Fifteen of the 21 massive “funnels” that will support the terminal were under construction beneath more than a dozen cranes. An army of ironworkers positioned rebar for the ground transportation center next to the terminal.

Two floors of the control tower rise at the center of the more than 12,000-acre site — more than six times the area covered by the capital’s existing airport.

“The risk of the (vote) is that the result may not reflect the level of technical decision the project deserves,” said Salvador Mora Velazquez, a political science professor at Mexico’s National Autonomous University.

Lopez Obrador has been labeled both a leftist populist and authoritarian. Letting the public decide the airport’s fate would seem to lean toward populism, but Mora sees something else at work.

“Political decisions taken through popular consultation or with the population’s opinion have a feel of legitimizing a decision already taken,” he said, adding that the way the questions are asked can steer the result.

A poll published this week by the newspaper El Financiero seemed to reflect this view. Using the official ballot question, a majority of those polled said the new airport should be canceled. Asked another way, a majority voted to continue it.

Carlos Slim, one of the world’s richest men, is pushing the new airport. His construction company is part of the consortium building the terminal and he believes the airport would have a wide-ranging impact on economic development.

According to Lopez Obrador, Slim has indicated that he and others involved in the project could help lower costs and possibly finance construction without public money.

The details of that proposal have not emerged, but it could be a way for the project to continue even with a negative referendum result.

“We understand the great pressure he’s under,” airport opponent Ignacio del Valle said of Lopez Obrador. “But we won’t accept that this project will be finished.”