Last week, the Austin City Council voted to back the Green New Deal, a national plan to tackle climate change that would overhaul the U.S. economy and energy sector. It was a big gesture from a city that prides itself on its environmental leadership. But, critics say, that gesture was undercut by a vote some local leaders took earlier that week – one that would drastically expand Interstate 35.

The Capital Area Regional Planning Organization Transportation Policy Board, on which some council members also sit, approved meting out $500 million to the Texas Department of Transportation to reduce highway congestion on 35. $400 million would go toward building out three new lanes on I-35 from Round Rock to Buda.

Supporters of the highway expansion, including the Real Estate Council of Austin, say adding lanes would help alleviate I-35’s notorious traffic. Before voting in favor of the measure, Austin Mayor Steve Adler called expansion the region’s "singular most important lift" when it comes to transportation planning.

But critics describe the project differently.

"It’s terrifying to me," said Susan Somers, a transit advocate and former member of Austin’s Multimodal Advisory Committee, a group that helped the city plan its long-term transportation goals.

"This is a massive, three-lane expansion that going to drive a lot of vehicles traveled and a lot of emissions."

Somers said voting to add lanes to the highway will make it harder to reach the goals set out in the city's Strategic Mobility Plan, which Council passed last month. The plan aims to reduce the number of single-occupancy vehicles by 2039.

"There’s a real disconnect there that’s really hard to understand," Somers said. "If you look at what Mayor Adler said after the Paris Climate Conference ... versus how this I-35 project is being presented is troubling."

Some of the disagreement over the plan centers on whether adding lanes to highways really helps fight congestion.

At the CAMPO meeting, Geoffrey Tahuahua, from the Real Estate Council of Austin, said projects like the highway expansion "are essential for our region to address congestion and increase mobility."

But, research shows that adding lanes can, in fact, increase traffic congestion as more cars flock to newly expanded roadways. That would have a negative impact not just on air quality, but also on the climate, as new roads service suburban and exurban subdivisions that are more energy-intensive to maintain.

The United Nations Intergovernmental Panel on Climate Change released a report Monday urging "rapid and far-reaching transitions" in cities to hold back the most catastrophic impacts of climate change.

Critics contend that even if Austin wanted to answer congestion woes by building more roads, it would not have the space to build new lanes.

"There is a physical constraint," said Steven Knapp, who also served on Austin’s Multimodal Advisory Committee. "It is impossible in many areas of the city."

If the I-35 project moves ahead, it’s total price tag is estimated to run around $8 billion. Knapp says some of that is money that would be better spent on transit projects.

"$2 billion could get us 19 miles of light rail right through the heart of this city," he said, "or we could spend $8 billion on I-35."

Advocates of the highway project might take issue with that comparison, as much of the state and federal money the I-35 project needs to move forward can only be spent on roads.

"I just don’t buy that argument at all," says AURA’s Somers, "I would rather build nothing than build something that’s going to make our climate problem worse."