After years of reconstruction, Longfellow Bridge reopened 5 a.m. Thursday

Pedestrians, cyclists and automobile traffic moved along the Longfellow Bridge on Thursday.Keith Bedford/Globe Staff

After five years of construction, frustration, and disruption, the Longfellow Bridge is expected to reopen at 5 a.m. Thursday, following a $300 million rebuilding project.

The bridge has been mostly shut down since 2013, limiting traffic to just one lane inbound to Boston, while barring cars headed outbound to Cambridge. MBTA Red Line trains that cross the Charles River on the bridge were replaced by shuttle buses on numerous weekends over the years.

The project was supposed to be wrapped up in 2016 but was delayed for reasons that included needing more time for historically accurate construction techniques, such as using rivets in order to preserve the century-old bridge’s period character. For several months, officials had said the span would reopen in May 2018, and on Wednesday night the state Department of Transportation confirmed it would meet that deadline — just barely.

The traffic configuration on the bridge will be different from what it was a few years back: one vehicle lane to Cambridge, compared to two formerly. The route into Boston will still have two lanes. And both sides will have bicycles lanes that are separated from motor vehicles by traffic pylons.

Even though the bridge will be open to cyclists, pedestrians, motor vehicles, and the Red Line, finishing all the work will take several more months. And another part of the project — replacing the nearby footbridge over Storrow Drive that connects Charles Circle to the Esplanade — is still under construction. That span is not expected to open until the fall.

Some cyclists aren’t happy with the plan for bike lanes and are pushing the state to dedicate more space for bicycles. They seek a design change that would dedicate just one lane to motor vehicles on the uphill slope from Cambridge to Boston, so that cyclists would have more room to pass each other during the climb.

So far, the state has said no, but it has promised to monitor car and bicycle traffic and make adjustments in the future.

Before construction began, about 28,000 cars a day crossed the bridge, according to state traffic counts. A separate count by the City of Boston in October 2017 that measured only traffic arriving from Cambridge found that cyclists accounted for nearly 12 percent of all vehicle crossings, and nearly 35 percent during the morning rush.

State officials declined to estimate the total cost of the reconstruction. But in a public presentation earlier this month, highway administrator Johathan Gulliver pegged the price at $306.6 million and said the agency was working with its contractors to limit the state’s share to that figure. Still, that would be well beyond the original budget of $255 million, because of the time delays and change orders. It would also be slightly above the $303 million the state set aside in case of unexpected costs.

As the work concludes, the state is gearing up to replace another major river crossing in Boston: An estimated $205 million project will rebuild the North Washington Street Bridge between Charlestown and the North End. It will start this fall and last five years. That’s according to the project schedule, anyway.