The car radio is playing something loud and twangy. It’s late summer, so bugs are peppering your windshield like dollops of rain as you speed comfortably in the wide, smooth lanes. And then you realize you just missed your dang exit.

Relax, partner—you’re in Texas. Just take the next one, and stay to the left as the off ramp descends towards the intersection. Follow the signage that leads you into the U-turn lane—a curving bypass that traces the underpass’ embankment. Without stoplights, cross traffic, or stress, you about-face to the other side of the highway and head back to where you’re going.

This sublime, forgiving bit of infrastructure is colloquially called a Texas Turnaround—officially, “Diamond Interchange U-Turns,” or some similar reconstruction. And while a protected lane just for whipping 180s might feel like utopic transportational indulgence, studies suggest they ease congestion, improve safety, and save drivers money on fuel.

Yet much like a good beef rib, it’s pretty hard find a Texas Turnaround outside the state. A dive into Texas history yields a half-answer at best. The longer explanation hinges on a cost benefit debate that even the Lone Star State has begun to question.

If there’s a heaven for drivers, Texans did the roadwork under the direction of infrastructure archangel Dewitt C. Greer. As head engineer of the the Texas Highway Department from 1940 until 1967, Greer paved tens of thousands of miles of highway throughout the state. One of his chief innovations was to flank every bit of it with frontage roads (what other places call service or access roads).

“These provided local access to property owners living along the interstates,” says Roger Allen Polson, co-author of Miles and Miles of Texas, which chronicles the state’s century of building roads. Polson says these frontage roads give Texas driving its characteristic wide-open feeling.

You can’t appreciate the impact of statewide frontages unless you grok how significantly America’s highways changed the act of driving. The key to efficiency for this massive system of roads was the lack of congestion-triggering cross traffic. Interstate highways applied the railroad philosophy of limited, logically-placed access-points to private car travel. It’s convenient for drivers, but a problem for the islands in the stream of traffic that lose out on all sorts of economic benefits. “If you have four miles between interchanges, you don’t provide access to that property in between,” says Polson.

Yet Texas law guarantees property owners access to roads that abut their land, and that includes highways. Greer wasn’t about to build on and off ramps according to property ownership, so instead lined every mile of highway with frontage roads that connected directly to all adjacent private property. And—bolstered by a 1946 amendment to the state’s constitution that directed three quarters of all special road taxes to be used on highways—he built them wide. “As far as I know, Texas is the only state with continuous frontage roads along all interstate highways,” says Polson. “It’s brilliant, and expensive, but it made landowners happy.”

But the frontage roads didn’t solve all the access issues. Due to space constraints in urban areas, many frontages run in one direction. That satisfied the law, but people who want to get from one side of the freeway to the other would have to drive to an under- or overpass, then make two left turns through intersections. “Left turns are the most complicated and time-consuming of any intersection activity,” says Marcus Brewer, a research engineer with the Texas Transportation Institute. They hold up traffic and disproportionately endanger both pedestrians and oncoming drivers. So, because urban frontage roads handle large volumes of traffic, even a small number of folks using those left turn lanes to flip their U-ies can cause major congestion.

It's a mystery exactly who came up with protected U-turn lanes as a solution to the left turn problem. But somehow the idea made its way into Greer’s Highway Department, where the big man almost certainly signed off on it. It's possible the idea came from rural parts of the state. “Texas has many places with high bridges spanning large rivers,” says Jane Lundquist, an engineer with the Texas Department of Transportation. “Turnarounds may have started as a convenience for local farmers or fishermen to use the lost space under the bridge near an abutment to return home.”

Engineers probably adopted these turnarounds for urban use once large “rivers of roadway” came to town, Lundquist thinks. It’s unclear who exactly made the suggestion, but the results are all over the state: access guaranteed, so dangerous left turn required.

In recent decades, turnarounds have popped up here and there outside of Texas. You’ll find them in Michigan and scattered throughout various Southern metropolises. New York City has a few. So do London, Sydney, and some cities in China. Mostly, though, they are a Texas phenomenon. The state’s Department of Transportation (successor to the Texas Highway Commission) doesn’t have an exact count, but estimates somewhere between 5,000 and 10,000 interchanges have at least one U-turn lane.

Despite this near-ubiquity, some Texas road contractors have started questioning whether turnarounds are worth the additional construction costs. Each U-turn lane can add a million dollars or more to the price of an interchange.

So the Texas DOT ran a study, which it published in September. “The literature review of previous research and old reports that show in general these U-turn lanes reduce delay, reduce emissions, improves environmental factors,” says Jonathan Tydlacka, a research engineer at the Texas Transportation Institute, and lead author of the study. U-turning cars that use turnaround lanes might also use between 60 to 80 percent less fuel than cars doing the same maneuver through an intersection. But the results weren’t definitive—not enough field research has been done to draw real, quantifiable conclusions about all the ways these local wonders might make traffic better.

But like so much in Texas, they certainly feel good, even if nobody can quite explain why.

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