Freight railroad CSX Transportation has reopened the Howard Street Tunnel, resuming train movements under the heart of Baltimore as the project to expand the rail line’s capacity nears completion.

Company, state and federal officials on Friday marked the completion of work that they said was critical for the future of the Port of Baltimore, where CSX plays a major role in moving goods to and from the Midwest, as well as up and down the East Coast.

The more-than-a-century-old tunnel was a mere 18 inches too small for trains carrying two stacked shipping containers to fit, a hindrance that officials said prevented the Port of Baltimore from competing with nearby ports where double-stacking allows rail carriers to move more on a single train.

“This site has been a choke hold,” said Sen. Chris Van Hollen, one of several speakers who took the podium just a couple hundred feet from the tunnel’s northern entrance as a train with the truck-sized containers stacked two-high towered over the crowd at the historic Mount Royal Station.

“We are now going to be able to dramatically increase business and jobs at the Port of Baltimore,” the Democratic senator said, “and that is a very big deal.”

“To the general public, this is nothing but an old, dark tunnel, but to the ILA, it’s a bright light for future” growth at the port, said Scott Cowen, president of International Longshoremen’s Association Local 333, which represents the port’s dockworkers. “That means jobs for the ILA.”

Cowen highlighted the effort to increase shipping container capacity at the port, largely through the ongoing expansion at Tradepoint Atlantic, a logistics hub on the site of the former Bethlehem Steel plant. He called the port the “economic engine of the state” after emphasizing the need to invest in its infrastructure.

“Without the engine running, we’ll all feel it,” Cowen said.

Enlarging the tunnel is part of an ongoing multiyear construction program that also includes raising clearances on more than 20 rail bridges between Baltimore and Philadelphia.

Train traffic is restarting in the tunnel, which runs from Camden Station, the MARC and Light Rail station next to Camden Yards, to the old Mount Royal Station, but trains won’t carry double-stacked cargo until the bridge work wraps up early next year.

Double-stacking will allow CSX to better compete for shipping business and ultimately mean fewer trucks on highways, said CSX CEO Joseph Hinrichs, who acknowledged “how important Baltimore is to CSX.”

CSX is the corporate heir to the Baltimore and Ohio Railroad, founded in the city as the nation’s first common carrier railroad.

Despite the tunnel belonging to CSX — the state doesn’t own it and no other railroads use it — Maryland taxpayers are footing most of the bill. The state committed more than $200 million alongside a federal grant of more than $100 million. CSX contributed roughly $140 million, with a small amount from Pennsylvania’s transportation department rounding the funding out.

CSX is a power player in Maryland freight transportation, owning a little more than half of the state’s 886 miles of rail that it uses to ship coal, chemicals and more throughout the eastern half of the United States. It moves millions of tons of Appalachian coal yearly through Western Maryland to its Curtis Bay terminal, one of two coal terminals that make the Port of Baltimore one of the country’s largest exporters of the polluting fuel.

To increase the Howard Street Tunnel’s clearance, crews dug out and lowered the railbed.

Baltimore City Councilman Jermaine Jones, a former labor organizer and union president, praised the use of union workers, who completed the job in just under eight months.

CSX originally planned to close the tunnel for 12 hours every day, allowing some trains to still roll through and the work to proceed at off hours, but opted for a full closure to finish construction sooner. The 16 daily trains that typically use the tunnel were diverted to longer routes around it.

The company saved about $48 million in the process, according to state budget records, but it’s unclear how those savings have been split among the funders.

It’s an example of a public-private partnership done right, an “example of what we can accomplish when we work together” that will “transform our supply chain,” said Rusty Roberts, a policy adviser at the Federal Railroad Administration.

The project, which spanned multiple federal and state administrations from conception to completion, represents a bipartisan progress in a time of extreme political polarization, Maryland Senate President Bill Ferguson said.

To cap the celebration, CSX invited company workers, local officials and reporters aboard one of its only passenger trains to ride through the tunnel itself.

The company obviously spared no expense on the train, which is outfitted with multiple dining cars, a full bar and glass-ceiling observation decks where state and company officials took in the passing tunnel lights from leather chairs. Gold and silver company emblems adorned the floors and walls.