Traffic & Transportation

Construction will narrow Idaho 55 to one lane this summer. The project starts this week.

If you’re one of the thousands of Treasure Valley residents who head north to the mountains around McCall and Cascade in the summer, you may want to factor a bit more travel time into your trips this year.

Parts of Idaho 55, the main route to the popular weekend destinations, will be under construction for part of the summer, according to Idaho Transportation Department spokesman Jake Melder.

ITD will repave the highway beginning at milepost 91 (about 12 miles north of Banks Lowman Road) and continuing about 7 miles north to Smiths Ferry. Construction is slated to start on Thursday, May 9.

According to Melder, the project contractor estimates finishing the construction in about two months, which would mean an ending date in late June.

Crews will work on the road one mile at a time, closing the two-lane highway down to a single lane during work hours on weekdays. Melder said flaggers or temporary traffic lights will signal motorists to take turns using the single lane.

“You’ll come up on the work zone, stop, allow opposing traffic to come through and then take your turn,” Melder said.

ITD anticipates allowing traffic through in 15-minute intervals. In a news release on May 7, ITD said to expect delays of about 30 minutes for your entire trip.

Construction and traffic on Idaho 55

According to ITD, the road north to mountain towns like Donnelly, Garden Valley, Cascade and McCall is already a site of major traffic on summer weekends.

A traffic summary for Fridays in June of 2018 showed an average of 17,200 travelers passing through the intersection of Idaho 55 and State Street, the bulk of them headed north. On Sundays, the bulk of travelers are heading south, back into the Treasure Valley.

In contrast, the Monday traffic average in June 2018 at the same intersection was about 11,800 travelers, evenly split in both directions.

Because of the significant uptick in weekend traffic, Melder said, ITD decided to suspend its construction project each Friday at noon. Both lanes of the road will be open until construction resumes at midnight on Monday, he said.

idaho 55 pothole.png
Idaho Transportation Department

Why construction on Idaho 55?

A series of harsh winters left the road pockmarked with major potholes, which crews have tried to fill in. And just last week, a 15-foot-deep mudslide closed a portion of the road that ITD intends to repair.

“The project came about because the roadway was deteriorating really quickly,” Melder told the Statesman in a phone interview.

According to ITD, inclement weather and rapidly changing temperatures this spring caused some of the pothole patch material to pop out.

“It needs a true fix,” Melder said.

That’s why ITD bumped up the repavement project, which was originally slated for 2021. Crews will mill off the existing pavement, mix new paving materials into that and lay down a fresh layer of pavement, Melder said.

Don’t hold out hope that the project will make that section of Idaho 55 any wider — Melder said because the highway is cut into the sides of hills and mountains, widening the road would be “extremely, ... almost prohibitively expensive.”

Fall construction

Another construction project on Idaho 55 is tentatively slated to start this fall, Melder said. It would involve flattening a mile-long stretch of the highway north of Smiths Ferry to Round Valley to improve safety.

According to an online project plan from ITD, “this section of Highway 55 has a 45 mph speed limit with narrow lanes, no shoulders, no guardrail in key locations, no clear zone most places, no clearance from rock cliff faces in other places, no separation from steep drop-offs, and curve speeds as low as 30 mph.

“The section of roadway has been identified as an area of safety concern with a crash rate approximately 33% higher than expected,” the plan says. “Data shows many of the crashes involve vehicles moving too fast, losing control and not having an opportunity to correct because of the narrow, winding road. ITD has identified alternatives and secured funding to improve safety and mobility on this corridor.”

The agency will alter the roadway to make it wider (32 feet wide instead of the current 24 feet wide) and allow for shoulders on both sides of the road. The project also will make curves more gradual and easy to navigate and add guardrails, pullouts and rock catch ditches.

Melder said the project will cost about $16 million, and ITD’s project site estimates the construction will last off and on during the spring and fall for about two years.

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