Milepost 43 Is Where New Harmony's I-15 Work Changes Direction

Get on I-15 northbound at Exit 42 and the Kanarraville rest area comes up within the first mile. Since spring 2025, that rest area has been the south end of a work zone. Shifted lanes, new pavement and crews on the shoulder run from there up past Hamilton Fort to the south end of Cedar City.

That project is close to finished. UDOT's next one in this corridor begins at the same milepost and heads the other way. It runs south from the New Harmony Interchange and rebuilds the bridges at Exit 42 and Exit 40. For anyone who uses Exit 42 to get to Cedar City or St. George, construction on this stretch of I-15 is not going away this winter. It is moving closer to home.

Two Projects That Meet at Milepost 43

Here are the two UDOT projects side by side, using UDOT's own project pages.

The northbound project is large. UDOT's March 26, 2026 construction announcement lists I-15 in Hamilton Fort at $91 million, and that figure includes rebuilding part of the I-15 bridge at Hamilton Fort. UDOT has not posted a cost or a contractor for the southbound project yet.

What Took Two Seasons North of the Rest Area

Thirteen miles of new lane is mostly digging, and the ground between Kanarraville and Cedar City made that harder. In July 2026, Construction Equipment Guide reported on contractor Suncore's progress. Before construction, a major high-pressure natural gas transmission line had to be relocated, and the design team had trouble pinning down where an existing waterline actually ran.

Once crews started digging, the same report says they hit "pop-up springs and boggy areas," along with weak subgrade soils that had to be over-excavated and reinforced with extra material and geosynthetics. Excavators also ran into a major basalt outcrop. They had to pry it loose, break it up with hammer attachments and haul it away by dump truck.

The weather helped. The first construction season was planned for June through October 2025. Utah then had an unusually warm, dry winter, so crews kept working straight through it.

The same article gives the expected life of the finished work. The new pavement should go 20 to 30 years before major rehabilitation, the roundabout 50 years or more, and the bridge 75 years or more.

Exit 51 Is Getting a Roundabout on Old Highway 91

Hamilton Fort's interchange is changing more than any other part of the northbound project. The old on- and off-ramps connected to the two-lane frontage road, Old Highway 91, which passes under the I-15 bridges. The rebuilt northbound side now ties into a single-lane roundabout. It's 180 feet across, sits on a 2.25-acre site, and has an 18-foot travel lane plus a 15-foot concrete truck apron. The rebuilt ramps are 2,000 and 1,200 feet long, and the report expected them to be finished in late fall.

The bridge was built in halves. Traffic used the old structure while one half of the new bridge went up, then shifted onto the new half so crews could rebuild the rest. The new single-span bridge is 153 feet long and, according to the report, "significantly wider than the old one." UDOT's project page shows a temporary bypass ramp onto northbound I-15 at Exit 51, in a drone photo dated August 27, 2026. It also says crews were close to finishing the new bridge and had started digging for the roundabout.

The Finish Date Depends on Which UDOT Page You Read

UDOT has given three versions of when the northbound project ends:

• "Before the end of the year," from UDOT's June 1, 2026 release.
• "Late Fall 2026," from the timeline on the project page.
• "Ending in early 2027," from the overview on the same page, which adds that schedules depend on weather and material availability.

As of late October, the project page still says traffic is shifted on northbound I-15 while crews build the third lane, and it still lists work on the west side of the Hamilton Fort bridge and earthwork for the roundabout. Daytime work runs weekdays from 6 a.m. to 5 p.m. Intermittent one-lane closures on I-15 are possible overnight, between 7 p.m. and 7 a.m. A late drive home from Cedar City is the one most likely to run into a lane closure.

When the climbing lane is done, the payoff is the one UDOT Region Four Director Kirk Thornock described in the June release:

"When this work is finished, it will be much easier for trucks, visitors and southern Utah residents to travel through this part of I-15."

Then the Work Moves to Exit 42

UDOT's southbound project page uses the same project language as the northbound one. UDOT plans a 5-mile passing lane on southbound I-15 from the New Harmony Interchange to Ash Creek Reservoir, mileposts 43 to 38, widening that side from two lanes to three. The project also rebuilds the bridges at the New Harmony Interchange, Exit 42, and the Kolob Canyon Interchange, Exit 40.

The timing is more settled than the page's banner makes it look. The banner at the top still says "Spring 2026 through Fall 2027." The overview and the timeline below it both say construction is anticipated to begin in early 2027, after a design phase that ran from Fall 2024 to Spring 2026. Even early 2027 is UDOT's estimate, not a fixed start date.

There are three things UDOT hasn't announced for this phase:

1. Any schedule for ramp closures at Exit 42 or Exit 40.
2. Any detour plan, including whether traffic would use Highway 144 or local frontage roads.
3. How access to Kolob Canyons will be handled while the Exit 40 bridge is rebuilt.

The northbound project gives a sense of what might come. That bridge was rebuilt in halves so traffic could keep moving. Whether UDOT uses the same approach at Exit 42 and Exit 40 is something the project team hasn't said yet.

The Kolob Side Before the Bridges Change

Exit 40 is how New Harmony reaches the closest part of Zion. Right now, the National Park Service lists the Kolob Canyons Visitor Center as open from 8 a.m. to noon and 1 to 5 p.m. The Kolob Wilderness Desk is closed until further notice. The Park Service says the Kolob Canyons Road is usually open but closes often in winter, including for snow and ice.

Dry days before winter closures set in are the easiest window for a drive up to the Kolob viewpoints. UDOT expects to start rebuilding the Exit 40 bridge in early 2027.

Getting Updates From the Project Team

UDOT runs a public information line for the southbound project. The hotline is 435-254-3305, and the email is [email protected]. To get on the update list, put "Project Updates" in the subject line. The New Harmony project page and the Hamilton Fort project page are where UDOT posts schedule changes, so they're the pages to check before a trip that has to be on time.

The interchange at Exit 42 is part of what makes New Harmony easy to live in, and it's about to change. If you'd like to talk through what this construction stretch could mean for a move, a listing or a build near Exit 42, Tayler Christensen and The Christensen Team are happy to share what we're seeing locally and keep you posted as UDOT releases more details.