PORTSMOUTH, New Hampshire — After 76 years of supporting traffic between Portsmouth, New Hampshire, and Kittery, Maine, the Sarah Mildred Long Bridge has been closed forever because of mechanical failure and the high cost to repair it amid construction of a replacement bridge.

William Boynton, spokesman for the New Hampshire Department of Transportation, said Wednesday morning the state DOT made the decision with Maine’s Department of Transportation after estimating the cost to repair the bridge would be about $1 million. Boynton said it would have taken more than six weeks to make the repairs to the bridge, which was previously scheduled to close permanently on Nov. 1. The new Route 1 Bypass bridge, already under construction, is scheduled to open in September 2017.

Boynton said engineers determined late Tuesday that the red-listed bridge is “not safe for routine operation without complicated and extensive repairs.” With its lift seized in the up position, maritime passage remains fluid on the Piscataqua River below, he said.

In a statement, Maine’s DOT said, “By keeping the bridge in this position, federal law, which requires a bridge to be accessible to marine traffic at all times, is adhered to.”

“Careful consideration has been given to the negative impact to motorists and the communities, versus the cost, time, and uncertainty involved in any repair of this magnitude,” Boynton said.

The bridge, which serves 14,000 vehicles daily, malfunctioned at about 11 a.m. Sunday, Boynton said. At that time the bridge’s lift span was stuck in the closed position, which meant vehicles could pass over it but large boats couldn’t pass under it.

At about 1:15 a.m. Monday, Boynton said, the lift span was raised because federal law mandates that river traffic take precedence over motor vehicles. Boynton said the cause of the malfunction is attributed to a wheel on a southwest corner tower, on the New Hampshire side, that carries cables for lifting the span.

Boynton said drivers should use detours that are in place, as well as the high-level Piscataqua River Bridge on Interstate 95 and the Memorial Bridge on Route 1, which links to Kittery from the Portsmouth downtown area.

According to the Maine DOT, the bridge was known for years as the “Maine-New Hampshire Bridge” until it was renamed in 1987 in honor of Sarah Mildred Long, an employee of the Maine-New Hampshire Interstate Bridge Authority for 50 years.

Construction of the new bridge is ongoing and has an estimated cost of $158.5 million. Mariners are lauding the design of the new bridge because it will allow straight passage beneath it, as opposed to an angular path needed under the current bridge. The new bridge also will have a 56-foot vertical clearance in its “resting” position, meaning 68 percent fewer bridge openings, according to the Maine DOT.

Distributed by Tribune Content Agency, LLC.