The Utah Department of Transportation began construction Tuesday in Brigham City on the state's third newfangled "diverging diamond interchange" Â where cars temporarily drive on the "wrong" left-hand side of the road to eliminate left-turn signals and help speed traffic.
"The way the construction has been phased, there will be no impact to traffic" until just before the project is completed in 16 to 18 months, said Vic Saunders, spokesman for UDOT Region 1. "They should be able to use the I-15 exit as they always have" at 1100 South in Brigham City.
That intersection connects to US 89/91 toward Logan.
The $12 million project will add a new bridge over I-15, just north of the existing bridge, and new signals. At diverging diamond interchanges, left-turn signals are eliminated by having traffic cross to the opposite side of the road as it travels over or under another road, and then switch back. Eliminating left-turn cycles cuts the time that traffic is stopped at signals, and helps reduce congestion.
"The big movement on the [existing] bridge has been westbound US-91 turning to southbound I-15. Because there is so much traffic using that movement, it makes it really difficult for cars on southbound I-15 that want to go east on 91 to find a space between traffic," Saunders said. "A lot of them have been going down into the businesses, doing U-turns and other things."
Saunders said the new design should not only improve mobility for Brigham City traffic "but also for Cache County because that is our major route to Logan."
UDOT recently built diverging diamonds at two busy urban interchanges, including at State Road 201 and Bangerter Highway in Salt Lake County and at the American Fork I-15 interchange in Utah County. The new one in Brigham City will be the first time the design has been used in rural Utah.