INDIANAPOLIS (AP) — Indiana Gov. Eric Holcomb marked the completion of a $4 billion, 142-mile extension of a major interstate highway Tuesday, calling it a “historic milestone” 16 years after work began on the project.

Holcomb’s two predecessors — former Vice President Mike Pence and former Gov. Mitch Daniels — joined him at a morning ceremony on Indianapolis’ southwest side, hours before Interstate 69’s southbound ramps to Interstate 465 were scheduled to open to traffic. Northbound ramps are set to open as soon as Friday.

Holcomb called the completion of the extension's 26-mile (42-kilometer) Martinsville-to-Indianapolis segment a “historic milestone." It's the final stretch of the 142-mile (229-kilometer) I-69 extension from Evansville to Indianapolis whose construction began in 2008. Some work on pavement and bridges will continue through the rest of the year in the Indianapolis area.

Before work on the extension began, I-69 ran from the Canadian border at Port Huron, Michigan, south to Indianapolis. Completion of the final link means it now runs continuously from Port Huron to Evansville.

The project spanned the administrations of Daniels, Pence and Holcomb, all Republicans. The highway, which was built in six segments, faced legal challenges from environmental groups but those failed to scuttle the project.

“There were a lot of cynics along the way, a lot of doubters that understandably wondered if it would be completed in their lifetimes," Holcomb told reporters Tuesday, The Indianapolis Star reported. "Today we prove that no project is too big.”

While work on the extension began in southwestern Indiana in 2008, construction of the final section that now runs between Martinsville and Indianapolis didn't begin until 2019.

That $2 billion final stretch upgraded 26 miles (42 kilometers) of State Road 37 to interstate standards and included construction of 10 new interchanges and more than 35 lane miles (56 kilometers) of local access roads through Morgan, Johnson and Marion Counties.