Northbound Interstate 75 motorists heading for downtown Monday morning should have alternate routes planned because the two downtown exits will close and will remain so for the next four years. The exits had not closed as of 5:30 a.m. Monday, but drivers should be prepared for when they do close.

The closing of the First Street and Third Street exits from northbound I-75 is part of the final phase of 16-year reconstruction of I-75 in Montgomery County. The southbound exits to those streets — both left-hand exits — will close in late November or early December, according to the Ohio Department of Transportation.

The exits will be eliminated and replaced by single northbound and southbound exits sometime in 2016, according to ODOT. When complete, the highway will have three lanes of traffic in each direction through the county.

The final phase is expected to take about four years and cost $126 million. The entire reconstruction will cost around $500 million.

“There is no simple way to do the construction on I-75,” said Dayton police Major Larry Faulkner, commander of the Central Patrol Operations District that includes downtown.

While local officials are expecting a rough first two days, Steve Finke, city deputy pubic works director, is certain downtown commuters and visitors are a resilient lot, having experienced the orange barrels along the interstate and elsewhere for more than a decade.

“The Stewart Street bridge (replacement) is a good example,” he said. “People were saying ‘We just can’t get around this.’ But they adjusted. Even with the University of Dayton basketball games, they adjusted.

“We have savvy drivers,” Finke said.

ODOT will have directional signs along the interstate south of Dayton alerting motorists of the closings. Suggested alternative routes include exiting at Edwin C. Moses or U.S. 35 east. Northbound motorist caught by surprise by the closings can get off the interstate at Main Street just north of downtown.