Center for American Progress

A Flawed Environmental Analysis Underpins I-35 Expansion in Austin, Texas

A Flawed Environmental Analysis Underpins I-35 Expansion in Austin, Texas

Instead of supporting the expansion of I-35, Austin should redirect funds toward expanding public transportation to provide residents with robust alternatives to driving.

Icy roads cause traffic delays on I-35 on February 15, 2021, in Austin, Texas. (Getty/Montinique Monroe)

Since 2000, Austin’s population has increased by 42 percent. The city’s rate of growth over the past 20 years has been more than twice as fast as the nation’s as a whole. This extended boom has placed enormous pressure on the regional transportation system—especially Interstate 35 (I-35). According to the Texas Department of Transportation (TxDOT), I-35 is the third-most congested roadway in Texas. In the dry and often clunky language of civil engineering, TxDOT states that I-35 “does not adequately accommodate current and future travel demand.”

In response, TxDOT, with the support of many but not all regional leaders, has decided to spend at least $4.5 billion to add four lanes to I-35 through the heart of Austin. Unfortunately, the analysis the state used to justify the project is deeply flawed, calling into question the entire undertaking as well as the lack of effective federal oversight of TxDOT’s planning work.

Building mega transportation projects comes with huge impacts on local communities and their surrounding environments. For this reason, Congress passed the National Environmental Policy Act of 1969, which requires project sponsors such as TxDOT to publish an environmental impact study before unleashing the bulldozers and paving machines. To truly understand the long-term consequences of construction, the state must look at regional impacts assuming the project is built (the build scenario) and is not built (the no-build scenario, or continuation of the status quo).

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TxDOT’s final impact report for the I-35 expansion project includes a detailed analysis of future traffic levels and emissions, including both greenhouse gases and toxic pollutants such as benzene and ultrafine particulate matter that get embedded deep in people’s lungs. The results are questionable, to say the least.

According to TxDOT, total driving on the central 8-mile segment of I-35 through Austin will increase by “45 percent between 2019 and 2050.” The state is assuming regional population growth will remain strong for decades to come, generating a lot more driving. But from here, things get weird. TxDOT claims that overall levels of driving and emissions would be essentially the same under the expansion of four lanes as they would be under the current I-35 highway. Additionally, the state claims that greenhouse gas and toxic pollution levels would be essentially the same for today’s I-35 versus after the expansion.

This makes no sense.

The state plans to add four new lanes to I-35 through the heart of the city. Yet we are to believe that overall levels of driving and, by extension, emissions will be essentially the same either way. For example, TxDOT estimates that, excluding materials and construction, greenhouse gas emissions from driving on I-35 will only be 7 percent higher after expansion than without expansion.

This level of logical contradiction about such a fundamental aspect of the project raises serious questions about the rest of the environmental impact analysis and the oversight and approval of TxDOT’s planning work.

Typically, a state must submit its impact review to the Federal Highway Administration (FHWA) for final approval before construction. The federal government’s job is to provide oversight, ensuring that states are conducting valid and accurate studies. However, in 2014, TxDOT decided to take advantage of a new federal program that allows states to take over the FHWA’s role, meaning that one part of TxDOT is conducting the environmental review and another part is signing off. This creates a loophole in federal law that allows the fox to guard the henhouse. Letting states check their own work is an inherent conflict of interest. The FHWA should begin an immediate review of TxDOT’s practices and revoke its ability to approve environmental studies should it find systematic errors.

It’s time for Austin and the larger metropolitan region to truly embrace a future with robust alternatives to driving to meet daily mobility needs.

The simple truth is that building more infrastructure for cars will lead to more driving. Research shows that expanding highways in rapidly growing regions produces only fleeting congestion relief. Within three to five years of opening, delays on I-35 will be similar to today. In other words, the congestion relief will be a blip; the scar on Austin will last forever.

The project also comes with a huge opportunity cost. The billions of dollars going to highway expansion could be spent in much more sustainable, equitable, and economically beneficial ways—including improved public transportation, biking, and walking infrastructure for the city of Austin. In 2019, Austin adopted a strategic mobility plan that set a goal of at least 50 percent of residents commuting by means other than driving alone. To date, the city has fallen far short of this goal. Expanding I-35 would further entrench auto dependence.

It’s time for Austin and the larger metropolitan region to truly embrace a future with robust alternatives to driving to meet daily mobility needs. A good start would be withdrawing the $633 million in local financial support for expanding I-35 and redirecting those dollars to enhance the 2020 voter-approved Project Connect plan to improve CapMetro’s service within the region. Austin residents and city officials have a fundamental choice to make about their city’s future. Expanding I-35 would lock in automobility for decades to come; to achieve a sustainable, equitable, and inclusive Austin, the city must choose a different path.

The positions of American Progress, and our policy experts, are independent, and the findings and conclusions presented are those of American Progress alone. A full list of supporters is available here. American Progress would like to acknowledge the many generous supporters who make our work possible.


Kevin DeGood

Director, Infrastructure Policy


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