As states and federal agencies continue to justify highway expansions by claiming they can help fight climate change, a closer examination of the evidence reveals a different story. The notion that widening roads can reduce emissions is a myth that has been debunked by decades of research and data. In reality, highway expansions lead to increased driving, more emissions, and a never-ending cycle of congestion.

The Texas Department of Transportation (TxDOT) recently released a report outlining its strategy to reduce pollution from its road network, which accounts for a mere 0.48% of global CO2 emissions. The report suggests expanding highways, citing reduced vehicle idling due to delay as a key benefit. However, this logic is flawed, and the results are predictable. As more cars are added to the road, traffic congestion will inevitably return, trapping us in a cycle of ever-increasing driving that makes it harder to slow the increase in global temperatures.

The concept of induced demand is the bane of highway expansion projects. As one researcher put it, "If you build it, they will drive." In Houston, average rush-hour journey times on the Katy Freeway lengthened by 15 to 20 minutes three years after TxDOT spent $2.8 billion widening it to 26 lanes. In England, researchers found that traffic moved more slowly than before the scheme opened. The blunt conclusion of a 2011 study in the American Economic Review is that adding road lanes "is unlikely to relieve congestion."

Wider highways convince more people to drive, which may increase car purchases and elongate commutes. The billions of dollars allocated toward highway expansions could instead be spent on projects that can credibly reduce driving, such as mass transit and dense development. "By adding more lanes to a highway, you're inducing more car-oriented land uses," said Wes Marshall, a licensed traffic engineer and author of the book Killed by a Traffic Engineer. "Zooming out, you're creating a much more auto-oriented environment, not just for that one roadway, but for the whole area."

The faulty logic is hard to dislodge, and the idea that wider highways are good for the planet remains widespread within state DOTs. Nevertheless, a small but growing number of state legislatures recognize the trade-off between environmental progress and roadway growth. Colorado and Minnesota have recently passed bills requiring state DOTs to minimize the climate impact of their investments. New projects that enable drivers to take shorter trips or travel by riding transit or a bike instead of driving a car ought to be able to easily pass muster, but highway widenings should not.

The Bigger Lie: How Widening Highways Actually Increases Traffic and Emissions

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