Weary commuters will have to wait four more months before they can start using the Sarah Mildred Long Bridge between Portsmouth and Kittery.

The lift-span bridge is now set to open to traffic in mid-May, eight months after cars were supposed to start using it to cross the Piscataqua River on the Maine-New Hampshire border, according to an updated construction schedule from Cianbro, the Pittsfield-based company hired by the state of Maine to build the bridge.

Cianbro spokesman Alan Grover did not respond to an interview request Tuesday to explain the delay.

Cianbro started construction on the $160 million bridge in 2015 to replace an aging lift span. It is one of the most expensive bridge construction projects in state history. The old bridge was closed permanently in August 2016 after the lift span became stuck in the upright position. It was demolished two months later. Drivers who typically use the bridge have been detoured onto Interstate 95 since it closed. About 15,000 vehicles used the bridge daily before it was closed.

In an email, Maine Department of Transportation spokesman Ted Talbot said the project is not over budget, but that Cianbro did not anticipate opening the bridge until spring.

“Maine and New Hampshire departments of transportation share the public’s frustration with Cianbro’s schedule. We are exploring all options,” Talbot said in a written statement.

The bridge opening was delayed by two months in September. At the time, the delay was blamed on a wet spring. A 4 million-pound steel span was installed at the center of the bridge in October.

The opening was delayed again in November. In late December, MDOT project engineer Ron Taylor told seacoastonline.com that Cianbro was still working on electrical and mechanical issues with the lift span before putting the bridge into service.

Talbot would not confirm Tuesday that mechanical and electrical issues were still delaying the opening.