A proposed road construction plan in Brigham City that could start as soon as next summer will impact Cache Valley drivers who have to travel through Box Elder County.

The existing on- and off-ramps from 1100 South in Brigham City to Interstate 15 will eventually be what is known as a “diverging diamond interchange.”

According to Utah Department of Transportation spokesman Vic Saunders, the project is in the design stage now.

Saunders said the Legislature appropriated $9 million last year for the project after the Northern Utah Chamber Coalition (made up of officials from Brigham City, Cache County, the Ogden-Weber area and Davis County) made it one of its top two priorities.

“With traffic numbers steadily increasing on U.S. 89/91 to Cache Valley, UDOT sees an important need to make the 1100 South interchange as efficient as it possibly can be to handle this increasing traffic load,” Saunders said.

The project is being constructed to help reduce a rising level of congestion with both the westbound U.S. Highway 91 to southbound I-15 movement at the interchange, and the southbound I-15 to eastbound U.S. Highway 91 movement.

“In many cases, there is so much traffic on westbound U.S. 91 seeking to go southbound on I-15 that vehicles waiting to turn east must wait an inordinate amount of time, or take chances and try to make that move during breaks in traffic that may or may not be long enough to safely do it,” Saunders said.  

Some drivers are also simply making a right turn on 1100 South, driving down to the truck stop west of the interstate, making a U-turn and then proceeding east on the highway. This translates into additional congestion for users of that business and the area around it.

Additionally, when traffic on westbound U.S. Highway 91 does stop for some reason, it quickly backs up all the way from the interstate to Medical Drive in Brigham City and beyond. It takes a significant amount of time for this traffic to clear out, increasing the congestion in that area.

“This has particularly been true in the case of major events in Cache Valley drawing high volumes of traffic from the Wasatch Front,”

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I-15

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Saunders said.

The diverging diamond interchange will result in a new structure added north of the present bridge structure over I-15. This new structure will handle the eastbound and eastbound to northbound I-15 movements on the highway.

The present bridge structure will be retained, and will handle the westbound, and westbound to southbound to I-15 movements on U.S. Highway 91.

All left-hand turn movements in such an interchange are “free turns,” meaning they don’t require a signal or a stop at a stop sign to make the turn. The only signals are at the crossing points of the interchange, where traffic occasionally must stop to allow through traffic to continue.

“Diverging diamond interchanges have proven to be very efficient movers of traffic in Utah, and often allow us to take advantage of existing traffic facilities, which also helps reduce the cost,” Saunders said.

General information about these interchanges can be found online at http://en.wikipedia.org/wiki/Diverging_diamond_interchange

A visualization is found at www.youtube.com/watch?v=WF9Cx0pMsbI. An animation of a Utah example of a DDI can be found at www.youtube.com/watch?v=CkMZN8w77IU.

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amacavinta@hjnews.com

Twitter: @amacavinta

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