Double-decker highways are back. But they’re not going to solve traffic jams

By Matt McFarland, CNN Business

Frederica Wilson, the US Congresswoman representing much of Miami, says she must leave home by 6:30 a.m. to beat traffic on South Florida’s highways.

“If I wait 10 more minutes, it’s too late,” Wilson, a Democrat first elected to Congress in 2010, said. “Then it becomes a literal parking lot.”

She doesn’t like traffic, and she hears from voters who say the same thing.

Wilson told CNN Business that she’s “absolutely overjoyed” that a double-decker highway is being built on a major east-west route to relieve congestion. It should be done by fall 2024. She’s also excited that President Joe Biden’s infrastructure bill will give states billions of dollars to potentially build other highway projects.

Florida is considering a double-decker project in Orlando. Texas has plans for double-decker roads in Houston and San Antonio. Double-decker highways have even received an endorsement from Tesla CEO Elon Musk.

But transportation experts caution that research has long shown that adding highway capacity in thriving metropolitan areas is a short-term fix. Congestion soon returns.

Florida leaders acknowledge this point, but they aren’t deterred.

“At some point in time, that particular double-decker road project will see congestion and then we’ll have to stake out another one,” Wilson told CNN Business.

Alfred Sanchez, CEO of the Greater Miami Chamber of Commerce, welcomes the double-decker highway too. He views it as a near-term solution that buys the area time to develop transit solutions that get people out of their cars.

“As population grows it’s only going to congest again,” Sanchez said. “This allows us the time to catch up.”

Highway builders haven’t been able to pave their way out of congestion in thriving areas because of the theory of induced demand. Increase the supply of something while lowering its price, and there will be more demand for it.

When more lanes are added to a congested highway, cars move faster and trips are quicker. The price of driving — in term of time spent — drops.

People then take longer trips and more trips by car, so there is more driving. Added highway lanes also attract more development, meaning more people and businesses use the highway than ever before.

The additional driving fills the new capacity. Highway projects that were launched so fewer people sit in congestion instead lead to more people sitting in congestion.

The experts say that the push for more highways is a relic of the mid-20th century, when early highway engineers focused on highway construction at the expense of other transportation modes, public health and the quality of people’s lives.

“We’re multi-modal transportation agencies now, and we’re communities that are more interested in moving people, goods and services [rather] than cars and trucks,” Roger Millar, the secretary of transportation in Washington State told CNN Business.

He said that states thinking about urban highways tend to look now to build better public transportation, add bike lanes, or change land use so a highway isn’t even needed. Urban areas are increasingly focused on repairing the damage of 20th-century highways, which disrupted urban communities, he said.

Double-decker highways emerged in the mid-20th century to move cars more efficiently in urban areas by building vertically. New York completed the double-decker West Side Highway by mid-century. Seattle built the double-decker Alaskan Way Viaduct in the 1950s. San Francisco built its double-decker Embarcadero Freeway, but halted construction in 1959 following local backlash.

Plans were stopped elsewhere. Paris scrapped a proposal to pave over a canal in the 1960s with a double-decker highway. The expensive roads earned a reputation as noisy polluters that blighted adjacent neighborhoods, much like the elevated railways that had already fallen out of favor. After a section of the elevated portion of New York’s West Side Highway collapsed in 1973 the highway was closed and later demolished.

Years before Musk and highway advocates called for double-decker highways, some states, like Millar’s state of Washington, chose to tear them down.

Washington removed the Alaskan Way Viaduct in Seattle in 2019. San Francisco did the same with the Embarcadero Freeway in 1991. Both were damaged in earthquakes and grew to be seen as eyesores that separated the cities from their waterfront.

California now looks to how to empower alternative transportation modes rather than just increasing freeway capacity, according to Bart Ney, a spokesman for the state transportation department.

“We see it time and again. Whenever we increase a freeway, the congestion grows to match the increase,” Ney said.

Musk has criticized this thinking, called induced demand, in which road expansions lead to more congestion.

“Induced demand is one of the most irrational theories I’ve ever heard,” Musk tweeted in 2019. “If the transport system exceeds public travel needs, there will be very little traffic.”

Robert Cervero, a professor at the University of California Berkeley who has documented how highway expansions haven’t solved congestion, said an urban area could probably eliminate congestion if it focused exclusively on doing so at the expense of other things that it values.

But cities are about more than moving people at high speeds in their cars, he said. Aesthetics, costs, place-making, quality of life and environmental factors matter. A city with highways so expansive that they never have traffic would be difficult to walk or bike in, which impacts public health and the toll we take on the environment. Such a space may soon begin to not even resemble a city.

“These things matter, and Musk doesn’t think of those things. That’s why we have planning and public policy making,” Cervero said. “Do you want to live in a place with 20-plus lanes all over the place?”

One city that tried the 20-lane approach is Houston. Interstate 10 stretches as wide as 26 lanes.

It still has frequent delays. One analysis found that the time it took for some trips increased by 30% in just three years.

The state is funding a project to add bus-only lanes on the highway.

Buses are far more space efficient than cars so can alleviate congestion. In Washington State, buses between Seattle and Everett carry almost 40% of the people moving on the corridor, but make up only 2% of the traffic, Millar said.

The failure of double-decker highways and underground highways to alleviate congestion in the long term is far from their only drawback. It’s much more expensive to build a double-decker highway. Asthma rates are higher in communities near highways, and adding more lanes contributes to pollution. Building up, rather than widening a highway, also doesn’t prevent the elimination of nearby homes and businesses.

Wisconsin considered building a double-decker highway in Milwaukee in recent years.

The state’s 2016 environmental study found that building a double-decker highway could cost three times the price of widening the highway. The double-decker option would have also displaced more housing units and had more impact on historic properties, as double-decker highways displace adjacent properties to build on and off ramps. The city of Milwaukee opposed the double-decker option and the state removed the option from consideration.

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