Rocky Mountain Power plans 54-mile transmission line along I-15 in southern Utah; public input sought

SALT LAKE CITY — Rocky Mountain Power has been holding a series of open houses regarding a large-scale power transmission line project in southern Utah.

Three Peaks to Purgatory Flat 345-kV Transmission Line Project is a 54-mile stretch of high-voltage power lines connecting the Three Peaks Substation northwest of Cedar City to the Purgatory Flat Substation in Hurricane. Current plans have the lines paralleling Interstate 15.

"As the communities continue to grow and energy needs increase, it becomes increasingly important to ensure that the regional transmission system can deliver electricity safely, efficiently and reliably," principal regulatory permitting manager Tami Moody said Wednesday. "The proposed transmission line is a part of Rocky Mountain Power's long term-planning efforts to meet those needs."

The initial transmission routing study for the project began in January of this year and went through May. The project, which is still in the beginning stages, is projected to be completed and in service by 2033. Public input is still ongoing and will continue throughout the project, officials said.

During the open house Wednesday — which was a virtual option that was held in addition to in-person options earlier this month — residents expressed some concerns. One made note of the lines running through her well; another expressed concern over privately owned ranches that may be affected.

Rocky Mountain Power officials said that it isn't a "done deal," adding that they will continue to take public input and "look at all the features on the ground that (they) cross" and "look to mitigate those and work with the property owner."

The idea of underground lines was brought up as an alternative; however, officials said that extra high voltage transmission lines "generally require substantially more excavation, substantially more ground disturbance during installation" and are more costly.

"Current estimates (of underground lines) is about 30-to-1 more expensive than overhead lines," said senior project manager Roger Yensen. "It's significantly more challenging to find that right-of-way, and it's more time-consuming, and repairs can take a lot longer — weeks versus days for underground versus overhead."

The projected power line route is adjacent to the entrance to Kolob Canyon's entrance to Zion National Park and the park visitor center, which was another concern brought up during Wednesday's open house.

Yensen said that Zion National Park "will be invited to be a cooperating agency throughout that process."

"The BLM in consultation with Zion National Park will determine if additional routes will need to be considered for that area," he added.

Environmental concerns were brought up, and it was noted that no environmental study has been completed yet.

Open houses started in the fall of 2026, with public outreach and permitting expected to go through 2030.

Engineering is projected to be between 2028 and 2030, with easement procurement from 2029 to 2031. Construction is projected to be from 2031 to 2033, with service to begin in 2033.

Ongoing information about the project as well as public comment submissions can be found online.

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