I-35 lane widths will shrink in Austin as TxDOT packs in more traffic

From KUT News:

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As the late morning sun beats down on the Tex-Best Travel Center in Kyle, truckers rest in their sleeper cabs while the white noise of I-35 roars a few steps away.

Pascual Fernandez, a seasoned truck driver with more than a decade of experience, is working on his Columbia Freightliner, a massive 18-wheeler used to haul tons of dirt around the busy construction sites of Central Texas.

The big rig measures 8 1/2 feet wide — the maximum legal limit in Texas. So Fernandez has concerns about a looming change coming to the Mexico-to-Canada freeway that slices through Central Austin.

The lanes will shrink 1 foot in width.

“If they narrow it, it’s going to be a little difficult,” Fernandez said. “When it’s tight, it’s pretty hard. You gotta concentrate and really focus on what’s around you so you won’t hit them.”

David Johnson, a truck driver from Atlanta working on his rig’s running engine in the blistering Central Texas heat, shared Fernandez’s concerns.

“When you’re driving an 18-wheeler, man, you gotta be more aware, more careful of your surroundings,” Johnson said, clad in a pristine white tank top. “So I don’t know why — why would they do that?”

The Texas Department of Transportation (TxDOT) is packing in more lanes through Travis County as part of the largest-ever expansion of I-35 in Austin. The biggest changes will happen through the center of the city, where four new “managed lanes” will be reserved exclusively for vehicles with more than one person inside.

TxDOT is narrowing the width of the lanes from 12-feet to 11-feet through most of Travis County including all of the highway from Ben White Boulevard to U.S. 290 East. The change is meant to squeeze in more capacity without farther expanding the interstate’s new footprint, which is already pushing out more than 100 homes and businesses.

The state has been using the power of eminent domain to purchase more than 54 acres of private property along the eight-mile stretch from Ben White Boulevard to U.S. 290 East — a costly and disruptive endeavor in a city with some of the highest real estate prices in Texas.

“We tried our best on this project to minimize displacements; that was a top priority,” said Heather Ashley-Nguyen, an engineer overseeing the interstate expansion.

Inside TxDOT’s Austin District Headquarters, Ashley-Nguyen explained how state and federal guidelines generally require freeway lanes to be 12 feet wide, as they are on almost all highways in Austin.

“Anytime we go below the desirable criteria, we write a robust reasoning why,” Ashley-Nguyen said, seated at a tidy desk in her office beneath the towering interchange at I-35 and U.S. 183.

TxDOT’s reasoning for shrinking lanes was approved by the Federal Highway Administration (FHWA), which has increasingly urged policymakers to consider going as narrow as 10.5 feet in urban areas to boost highway capacity without seizing as much land.

The two agencies collaborated extensively, holding multiple meetings to craft the lane configuration for Austin. The FHWA said federal approval was only granted after TxDOT provided a careful safety and operational analysis.

Narrowing lanes maximizes available space, but makes driving more difficult at similar speeds, which could have safety implications for a highway used by some 200,000 drivers per day.

While lane slimming has been hailed as a sensible measure to slow drivers on local streets, academic research is mixed on the safety effects of squeezing motorists along limited access freeways like I-35. Research sponsored by TxDOT and the FHWA found highway drivers only reduce their speed by an average of two miles an hour when lanes are cut down to 11 feet.

As highway lanes across the United States narrow, the nation’s vehicles are expanding — leaving less space between them.

“Vehicles have definitely gotten bigger, and they’re also getting heavier,” said Russ Rader with the Insurance Institute for Highway Safety, a Virginia-based nonprofit that tests and rates vehicle safety for insurers.

“A big part of that is the proportion of the vehicle fleet that is made up by SUVs and pickups has grown substantially, especially over the last 10 to 15 years,” he said.

Ashley-Nguyen argues lane width is only one of many factors in highway design, which requires tradeoffs between safety and mobility. TxDOT engineers typically trim down frontage roads, managed lanes, and merge lanes before reducing main lane widths. Highway shoulders are the last to be slimmed.

“We have a lot of operational improvements that just in general provide a much, much better design,” she said, pointing to longer merge lanes, frontage road lanes that let people bypass intersections, and the elimination of the upper decks.

The state’s federally-required environmental study says adding 32 miles of lanes through Central Austin will reduce crashes by 29%. Critics respond that crash rates will go up as congestion returns to what has become the city’s deadliest road.

“TxDOT’s playbook has hundreds of design guidelines for their single-minded roads and highways,” Sinclair Black, a famed local architect and longtime critic of I-35, wrote to the state agency when it was taking public feedback on the highway expansion. “A few pretend to make their overall design safer, which clearly isn’t working.”

Texas has already experimented with narrower lanes in Dallas, Houston and San Antonio. TxDOT’s Austin District approved 11-foot lanes for the 183 North Project — a $612 million tolled expansion for nine miles between state Highway 45 North and MoPac, scheduled for completion in 2026.

Some of the only 11-foot-wide highway lanes in Austin are on MoPac from Lady Bird Lake to 2222. They were narrowed to make space for the MoPac Express Lanes, also 11-feet wide, which opened in 2017 with tolls that go up or down based on how busy traffic is. In 2020, a stretch of U.S. 183 near I-35 was reconfigured to add a lane by shrinking the width of existing lanes from 12-feet to 11-feet.

Compared to I-35, MoPac has significantly less heavy truck traffic, one of several factors that can affect the safety of narrower lanes, according to research from the Texas Transportation Institute (TTI), a state-funded think tank at Texas A&M University.

About 2.4% of traffic on MoPac is made up of heavy truck traffic. Along the international commerce corridor of I-35, more than 9% of vehicles are big rigs and delivery trucks, according to TxDOT data.

“Twelve-foot lanes have less total crashes and fatal and injury crashes than 11-foot lanes. Twelve-foot lanes have a better record,” said Robert Wunderlich, a research engineer who directs TTI’s Center for Transportation Safety. He says shoulder widths are even more important than the size of the lane when it comes to reducing crashes.

Other research has found using 11-foot-wide lanes to increase capacity could temporarily improve safety by allowing cars to drive at a more consistent speed.

“Because now you’ve got smooth flow at relatively low speeds, as opposed to this bottlenecking. That’s very unsafe and leads to a lot of crashes,” said David K. Hale, a civil engineer with the Washington, D.C.-based research company Leidos whose research into bottlenecks was funded by the FHWA. “You think you’re going to be flowing but all of the sudden people are stopping and slamming on the brakes.”

But Hale says such improvements tend to be short-lived because smoother traffic flow attracts more drivers “to the point where it’s just as congested as it used to be, but now you’re just serving 20% more trips but at the same congestion level.”

“Some people would still call that a victory,” he said, “whereas others may say that if it’s just going to go back to being congested, they don’t want to invest perhaps in a solution like that.”

Construction began in 2022 on the I-35 Capital Express South expansion, where tall columns of concrete that will support stacked lanes are already taking shape. The lane additions on I-35 CapEx North started last year.

The biggest part of the highway expansion, the I-35 Capital Express Central project through downtown Austin, is just getting underway. TxDOT has hired a company to begin work to widen the Martin Luther King Jr. Bridge over I-35.

Drivers should begin to notice construction on I-35 CapEx Central within the next couple of months, a TxDOT spokesperson said. By early 2025, work crews will be digging into the first major phase of the expansion, starting to pack in more lanes from Ben White Boulevard to Holly Street.

This story has been updated to include a safety and operational analysis by TxDOT that led the FHWA to approve the narrowed lanes on I-35. A mention of 11-foot-wide lanes on a stretch of U.S. 183 near I-35 was added.

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