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New intersection type coming to Utah
This is an archived article that was published on sltrib.com in 2010, and information in the article may be outdated. It is provided only for personal research purposes and may not be reprinted.

A new type of street design is coming to Utah that is aimed at entirely eliminating left turns at congested intersections to help speed along through-traffic. To go left, drivers will need to do a combination of right and U-turns instead of a normal left.

Those types of intersections are known elsewhere as "Michigan Left Turns" or "Michigan U-Turns," because they were used first in that state and are common there. The Utah Department of Transportation is calling its version instead a "ThrU Turn Intersection," or TTI for short.

UDOT is studying installing the first one at the gateway to Draper at 123rd South and Minute Man Drive (a frontage road that is an extension of State Street), just east of I-15. Construction could begin next spring depending on the outcome of current environmental and design work.

"That intersection is already so congested that it is essentially failing with long delays," said Adan Carrillo, who handles community outreach on the project for UDOT. "We studied a lot of options there, and this is the one that appears to work the best."

UDOT considered a "Continuous Flow Intersection" that it has been recently building on Bangerter Highway. That design eliminates traditional left turn lanes by creating new left-turn lanes several hundred feet back from the intersection, then uses signals to allow cars to cross traffic into new lanes at the far-left of the roadway so that cars can turn left at the same time through-traffic goes straight.

Carrillo said extra lanes for such interchanges would have required demolishing some buildings, or would have cut off access to some businesses — as would some other options, including possibly building some bridges for traffic. He said the new option requires taking only some slices of property that should not interfere greatly with businesses, and maintains all current access.

"Doing nothing also is not an option. Traffic would just get worse with expected development in the area," Carrillo said.

UDOT studies show that in the future the intersection would be so congested that wait times of up to seven minutes would be required to make some left turns. It could also cause serious backing on 123rd South and on I-15. Moving left turns away from the intersection will provide more green-light time for through-traffic, and help reduce congestion.

Michigan started using such intersections in 1960, and has them throughout that state. Although Michigan has used them for 50 years, the MichiganHighways.org website said other states were slow to adopt them until recently.

That web site, which includes instructions on how to navigate the intersections, says, "Often maligned, often misunderstood, the Michigan Left Turn is an operation which causes much consternation among out-of-state drivers and nary a second thought from locals." —

A new left-turn scheme

Following are some examples of how the proposed new design would work in different directions. (An animation is available online at youtube.com/watch?v=SUuqugEddcI).

For eastbound motorists on 123rd South seeking to turn left on Minute Man, they would instead turn right. Then, they would travel several hundred feet down Minute Man to the intersection with 12450 South, where signals will allow traffic to make a U-turn and head back in the desired direction.

As another example, northbound motorists on Minute Man desiring to turn left onto 123rd South would need first to drive straight through that intersection. Several hundred feet down the road, they would make a U-turn at a signalized intersection to return to 123rd South to make a right turn there.

Traffic • Draper has been picked for the first Utah test of a 'ThrU Turn Intersection.'
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