When Interstate 25 was constructed through Denver, highway engineers moved a river.
It was the 1950s, and nothing was going to get in the way of building a national highway system. Colorado’s governor and other dignitaries, including the chief engineer of the state highway department, acknowledged the moment by posing for a photo standing on bulldozer tracks, next to the trench that would become Interstate 25.
Today, state highway departments have rebranded as transportation agencies, but building, fixing and expanding highways is still mostly what they do.
So it was notable when, in 2022, the head of Colorado’s Department of Transportation called off a long planned widening of Interstate 25. The decision to do nothing was arguably more consequential than the alternative. By not expanding the highway, the agency offered a new vision for the future of transportation planning.
In Colorado, that new vision was catalyzed by climate change. In 2019, Gov. Jared Polis signed a law that required the state to reduce greenhouse gas emissions by 90 percent within 30 years. As the state tried to figure out how it would get there, it zeroed in on drivers. Transportation is the largest single contributor to greenhouse gas emissions in the United States, accounting for about 30 percent of the total; 60 percent of that comes from cars and trucks. To reduce emissions, Coloradans would have to drive less.
An effective bit of bureaucracy drove that message home. After sustained lobbying from climate and environmental justice activists, the Transportation Commission of Colorado adopted a formal rule that makes the state transportation agency, along with Colorado’s five metropolitan planning organizations, demonstrate how new projects, including highways, reduce greenhouse gas emissions. If they don’t, they could lose funding.
Within a year of the rule’s adoption in 2021, Colorado’s Department of Transportation, or CDOT, had canceled two major highway expansions, including Interstate 25, and shifted $100 million to transit projects. In 2022, a regional planning body in Denver reallocated $900 million from highway expansions to so-called multimodal projects, including faster buses and better bike lanes.
Now, other states are following Colorado’s lead. Last year, Minnesota passed a $7.8 billion transportation spending package with provisions modeled on Colorado’s greenhouse gas rule. Any project that added road capacity would have to demonstrate how it contributed to statewide greenhouse gas reduction targets. Maryland is considering similar legislation, as is New York.
“We’re now hoping that there’s some kind of domino effect,” said Ben Holland, a manager at RMI, a national sustainability nonprofit. “We really regard the Colorado rule as the gold standard for how states should address transportation climate strategy.”
That won’t be easy. States have almost unilateral power to determine how billions of dollars in federal transportation funding is spent. A recent analysis showed that more than half of $1.2 trillion enabled by the Infrastructure Investment and Jobs Act of 2021 will be spent on highway expansion and resurfacing.
“In order to fundamentally change how most federal transportation dollars are spent,” said Shoshana Lew, the executive director of Colorado’s transportation agency, “you have to get into the network of state D.O.T.s.”
In other words, the people most likely to reduce cars on the road are the ones who have long prioritized them.
More lanes, more cars, more greenhouse gasses
People have been fighting highway expansions for as long as there have been highways. In recent years, activists in Houston, Los Angeles and Portland, Ore., have fought widenings, arguing that the increased exhaust would worsen air pollution and exacerbate high rates of asthma in Black and Hispanic neighborhoods.
In Denver, a fight started in 2014 when the transportation department announced a plan to triple the width of Interstate 70, which runs through majority Hispanic neighborhoods in North Denver. Growing up, Ean Tafoya would stand in his front yard, in the shade of a century-old maple tree, and look north at the highway’s elevated lanes. Beyond the highway, a smokestack at a nearby oil refinery billowed toxins. His neighborhood was among the most polluted in America, and residents experienced significantly higher rates of respiratory diseases than those elsewhere in Denver.
Mr. Tafoya was working for the City Council when he heard about the plan to expand the highway just blocks from where his mother still lived. “I-70 radicalized me,” he said. He quit his job and helped organize a statewide coalition of activists and community members who tried to stop the Interstate 70 expansion with lawsuits and protests. In the end, Interstate 70 was expanded. But the fight served as a warning to leaders like Ms. Lew that future highway construction would face spirited opposition.
At the same time, a larger reckoning with how transportation decisions affect greenhouse gas emissions was playing out.
The basic principle linking wider highways to more carbon emissions has been well understood since the 1960s. Back then, an economist rebutted the prevailing assumption that adding lanes would fix traffic, showing instead that wider roads only increased the number of cars and made congestion worse. This phenomenon came to be called “induced demand.”
State transportation departments nonetheless consistently underestimate how highway expansion leads to more driving. In 2019, a team led by Susan Handy, a professor of environmental science at the University of California, Davis, developed an induced demand calculator to help others translate how specific expansions led to more cars on the road.
In Colorado, Mr. Holland and several other climate activists used Dr. Handy’s calculator to do more than measure increased driving. In 2021, they modeled the greenhouse gas effects of all the projects in the state transportation’s agency’s 10-year plan, which included more than 175 miles of lanes added to highways. They found that the projects could increase annual greenhouse gas emissions by the equivalent of 70,000 more cars and trucks on the road.
The transportation agency disputed the figure, but the calculation nonetheless changed the conversation, Mr. Holland said. Until that point, “nobody was actually putting real emissions numbers behind highway expansion,” he said. The analysis galvanized climate activists, who had largely left highway fights to people like Mr. Tafoya, those living in communities directly affected by expansion.
In June 2021, when Governor Polis signed a $5.4 billion transportation funding bill, it included a requirement that the Transportation Commission of Colorado, which oversees CDOT, make a plan to reduce transportation-related greenhouse gas emissions. Other states had tried to reduce emissions from transportation, but with little effect because there were few consequences for failing to do so. Activists in Colorado were determined that this rule would be different.
Mr. Tafoya, who was by then the Colorado director of a national advocacy group called GreenLatinos, showed up to the transportation commission’s monthly meetings and submitted detailed comments on the draft rule. When it passed in December 2021, the rule contained the forceful incentive tying emissions targets to funding.
Six months after the rule passed, on a hazy morning in June 2022, advocates gathered in a bike lane with Interstate 25 thrumming behind them and asked CDOT not to widen the highway. This time, they had leverage.
Why electric cars aren’t enough
If every car on the road were battery-powered and those batteries were charged entirely by renewable energy, transportation emissions would be close to zero. But the average car on the road is 12 years old, meaning that every gas-powered car sold today will emit carbon for at least another decade. And even though President Biden’s administration has invested tens of billions of dollars to stimulate electric vehicle production and infrastructure, electric cars accounted for just under 8 percent of new cars sold in the United States last year.
“The scale of the challenge to getting a net-zero transportation system is, I think, much bigger than folks want to acknowledge,” said Costa Samaras, the director of the Wilton E. Scott Institute for Energy Innovation at Carnegie Mellon University. To meet emissions targets, “ridiculously high levels of electrification” are needed, he said. “We also, at the same time, need to be building the types of communities that enable folks to move around without needing to rely on a car.”
How, exactly, to do that is the challenge now facing Colorado’s transportation department. The emissions rule does not prevent highway expansions, and several are still being planned. But the agency has begun a significant shift. When Ms. Lew was appointed in 2018, she observed that the work force “was very rooted in the old culture of highway building,” she said. “I think that actually goes part and parcel with some of the overemphasis on these big highway widening projects.”
When the proposal to widen Interstate 25 came up, Ms. Lew took several things into consideration. The “tremendous amount of controversy” that surrounded the Interstate 70 expansion — the one Mr. Tafoya had tried to stop — was one issue.
The widening was also unlikely to fix traffic: Years earlier, the agency had spent $800 million to expand another stretch of Interstate 25 in south Denver and ended up with worse congestion than before construction began.
Perhaps most important, the department couldn’t expand Interstate 25 and meet its newly mandated climate targets. “We can’t get there with electrification alone,” said Kay Kelly, CDOT’s chief of innovative mobility. The transportation agency, she said, now has to think harder about ways “that allow people to get places without a car.”
For years, Denver had been trying to build bus rapid transit, which runs more like a light rail than traditional bus service, with faster travel times and more frequent service. Then came the greenhouse gas rule, which quickened that effort by years, Ms. Lew said.
In 2022, the agency allocated $170 million for bus rapid transit in Denver and $120 million for Bustang, a statewide bus service, over the next decade. Late last year, Ms. Lew announced CDOT’s first three rapid routes, including one along 18 miles of Federal Boulevard, which runs north-south across the city, roughly parallel to Interstate 25.
“It’ll come so frequently that you won’t need to read a schedule,” said Ryan Noles, who was hired last year to lead the transportation agency’s new bus rapid transit program. Mr. Noles hopes that CDOT will break ground on the Federal Boulevard rapid bus line in 2027, with riders on board by 2030.
That won’t be soon enough to have an impact on the state’s 2030 carbon emission reduction goals, which it’s not likely to hit. Building new transportation, even without changing the course of a river, takes time. And when the new bus line is up and running, lots of people still have to change their daily habits. Reducing emissions from transportation, Ms. Kelly said, requires changing the behavior of “millions of people and dozens of decisions that they make throughout their daily lives.”
Which comes first, transit or housing?
On a bright, unseasonably warm day in January, I met Danny Katz, the executive director of the nonprofit Colorado Public Interest Research Group, near the Decatur-Federal Station, one of the busiest transit stops in Denver and a future stop on the bus rapid transit line. We walked down Decatur Street toward the South Platte River, the one that was once rerouted to accommodate Interstate 25. The sounds of construction — the slow beeps of a truck in reverse, a pile driver pounding the hard earth — filled the air. But the machines aren’t for highways; they are for housing.
Over the coming decade, tens of thousands of housing units will be built within a two-mile radius of this spot. “This is the perfect place not to widen a highway,” Mr. Katz said. If transit is going to work anywhere, he said, it’s here.
To make it possible for people to drive less, they need to live closer to where they are going. “I think where we stand now is that the real frontier is around land use,” said Will Toor, the executive director of the Colorado Energy Office, a state agency responsible for reducing emissions. Changing zoning laws to allow for more dense development could reduce emissions in Denver by 8 percent, largely by reducing the distance and frequency people have to drive, according to a 2023 study by RMI.
Governor Polis agrees. After a sweeping land use reform bill failed last year, he focused on smaller measures to increase the state’s housing supply. In May, he signed laws to create incentives for denser housing development near transit stops and to allow accessory dwelling units to be built in more neighborhoods. “Big efforts often take several years,” Mr. Polis said in an interview. “Most people don’t want to have 45-minute commutes each way. They do it out of necessity and affordability. So housing opportunities that people can afford close to job centers means less travel in a car, less emissions and less time lost in traffic.”
Housing and transportation, in other words, are intertwined. Unlike most state transportation directors, Ms. Lew did not study engineering. She has a master’s degree in American history and a background in finance. Transportation represents most of the federal investment in cities, she said. But until recently, investing in transportation largely meant following a playbook written in the 1950s, building grand concrete structures that efficiently swept cars from one side of a city to another.
No longer. In 1958, the year that Interstate 25 opened to traffic, the State Highway Department constructed the sweeping interchange connecting Federal Boulevard to Colfax Avenue and demolished more than 240 homes and businesses in the process. That project, which shaped the city for half a century, might now be undone. In March, CDOT was awarded a federal grant to remove the cloverleaf and rebuild the street grid, complete with storefronts and apartment buildings full of people. And, if Ms. Lew is successful, a rapid bus to take them where they need to go.
Megan Kimble is an independent journalist based in Austin, Texas, and the author of “City Limits: Infrastructure, Inequality and the Future of America’s Highways” (Crown 2024).
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