DAYTON — Major construction work on Interstate 75 through downtown is expected to continue until 2017.

The first phase of the project — a $122 million rebuild of I-75 in the area of Ohio 4 — is nearly complete. Work started in 2006 on Phase 1A, which included adding a third lane to eliminate traffic congestion, removing a sharp curve and left-hand ramps.

“This area was identified throughout the whole Interstate 75 corridor through Ohio as a real ‘bottleneck,’ ” said Randy Chevalley, deputy director of the Ohio Department of Transportation’s District 7.

Planning for the more than $400 million modernization project, done in three phases, began in 2000. Federal highway funds paid for about 90 percent of the total, with the state of Ohio funding the remaining 10 percent, Chevalley said.

“From the get-go, we’ve tried to say this was going to be a long haul,” Chevalley said.

Phase 1B, a $58 million job creating three continuous lanes on I-75 in the U.S. 35 area, is scheduled to end by June 2013.

The section in the middle of those two projects, Interstate 75 through Dayton’s central business district, marks the final phase. Construction will cost an estimated $230 million and is currently in the design stage.

This work involves closure of ramps to Dayton’s central business district with traffic detoured to South Jefferson Street off U.S. 35 and North Main Street.

The southbound side of the interstate will be constructed first, with all traffic detoured to the northbound side.

Chevalley said the final phase of the project should have a contractor on board by fall 2012.

“This isn’t your average humdrum, day-to-day construction project that ODOT gets involved with. This is probably the most complex project we’ll see in our district and that we have seen for a long time,” Chevalley said.