Rehabilitation of a pair of Hamakua bridges on Hawaii island will begin later this year, but likely at an inflated cost from previous estimates.

Shelly Kunishige, spokesperson for the state Department of Transportation, said the state is expected by the end of March to award a contract to rehabilitate the Nanue Stream Bridge on Highway 19.

Located at about the 15-mile marker, the 286-foot-tall bridge — the tallest on the island — was found to be in an advanced state of deterioration in an environmental assessment published in 2024. Because of that, the state will undergo a three-year rehabilitation project that will replace the structure’s trestles and girders.

Kunishige said that once the bid is awarded, construction can begin shortly thereafter, unless the award is challenged.

Once construction begins, single-land contra-flows will keep the bridge open to traffic, although the EA noted complete bridge closures might be necessary periodically.

Kunishige also said the bids are coming in higher than the initially anticipated.

In 2022 the Nanue project’s price tag was estimated at roughly $25 million, but the DOT said in January 2024 that the estimated cost of rehabilitating the bridge was $43 million. Just five months later, in June, Kuni­shige said the estimated cost of the project was $80 million.

In 2024 the DOT was awarded $74 million from the federal government to rehabilitate both the Nanue bridge and the Hakalau Stream Bridge, farther south on the Hamakua Coast. The state will provide the remainder of the funding.

The Hakalau bridge is in similarly poor condition and requires a lengthy rehabilitation project. Kunishige said that project is expected to begin late this year.

The Hakalau project is estimated to cost $78 million, according to a 2024 environmental assessment.