Portal North Bridge's debut in N.J. will result in extensive Amtrak schedule changes. Here's what to know.

The Portal North Bridge in New Jersey is nearing completion, and when done will mark a major milestone for commuters along the Northeast Corridor.

Bringing it online, however, will mean about a month of disruptions for hundreds of thousands of rail commuters.

Schedule changes, slower trains  

The big changes start this weekend. On Sunday, Amtrak will shift train traffic off the more than 100-year-old Portal Bridge and onto the brand new bridge over the Hackensack River.

As a result, only one track will be open between Newark and Secaucus over the next four weeks, meaning schedule changes and slower, more crowded trains.

In addition, Midtown Direct service will be rerouted to Hoboken during the work, and alternate routes like PATH trains, ferries, and the 126 Bus will be busy, too.

Sean Caldwell DJs in front of Madison Square Garden a few nights a week, and relies on the trains to get all his gear into Manhattan.

"I'm bringing so much equipment into the city. Like, really, I'm taking up about two or three spaces of people, so it really affects me because I do want to be courteous to others," Caldwell said.

Regular schedules are expected to return March 15. Until then, officials are urging commuters to plan ahead, check schedules, and, if possible, work from home.

"It removes one of the bottlenecks"

Experts say despite the inconvenience, the work is overdue. The old Portal Bridge is notorious for sticking, causing delays up and down the busiest rail corridor in the U.S.

"This piece, while this doesn't kind of fix the whole corridor, what it does is it removes one of the bottlenecks, one of the causes of delays that have frustrated commuters for decades now," said Tom Wright, president of the Regional Plan Association.

NJ Transit President Kris Kolluri says a month of pain guarantees long-term gain.

"This bridge literally has not been in good shape for decades, and for the first time in 100 years, we're about to build a brand-new bridge and open a brand-new bridge so we can increase reliability," Kolluri said.