A final environmental review of plans to reshape almost six miles of Interstate 20 through Vicksburg should be sent to the Federal Highway Administration sometime this fall, state highway officials said this week.

Discussed for years, the project would widen the interstate between the Washington Street/Warrenton Road exit and the U.S. 61 North/Mississippi 27 exit to three lanes in each direction and rebuild interchanges at Halls Ferry Road, Indiana Avenue, Wisconsin Avenue and Clay Street.

Jackson-based Neel-Schaffer Inc. is doing the study. Once complete, the effort moves to buying rights of way, relocating utilities and, ultimately, construction, according to an update of highway work this week by the Mississippi Department of Transportation.

Total costs are pegged at $100 million, though the agency expects it to approach $1 billion once all work is done. No timetable for construction has been identified. Study and design phases are funded through this year at $2 million.

Both frontage roads would be turned to one-way streets while the interstate is being widened, according to two alternatives presented in a public hearing in Vicksburg in 2009. The difference between the two plans is what will happen afterward — one version keeps traffic westbound on North Frontage Road and eastbound on South Frontage Road, while the other returns to two-way traffic.

A flyover ramp would replace a left-handed exit onto U.S. 61 South from Halls Ferry Road, plans showed. Underpasses just east of Halls Ferry Road and near Porters Chapel would link the two frontage roads. South Frontage Road would be extended over rail tracks near the Outlets at Vicksburg, part of the plan for which Ridgeland-based Wilbur Smith Associates has completed a right-of-way review. Plans also showed wider approach ramps onto I-20 from Clay Street.

In a separate effort, an environmental study on how to rework Mississippi 27 from U.S. 80 to Warren Central High School continued this week with another meeting of consultants and MDOT representatives. Issues with drainage and elevation must be ironed out before a document is sent to the FHA, MDOT said.