A study to find any environmental impacts on Bayou Pierre if U.S. 61 is four-laned through Port Gibson is expected to be presented this year, according to the Mississippi Department of Transportation.

The review, conducted since 2010 by Michael Baker Jr. Inc., will determine whether a straight shot through the city would result in a net rise in the stream, which runs near the north end of town.

MDOT has not seen the study, but it is finished, said Michael Arnemann, an assistant to Central District Commissioner Dick Hall. About $900,000 in state money was to be used to finance a design phase by this year, according to the agency’s Statewide Transportation Improvement Program for 2010-13.

Use of state money exclusively would not bind the agency to comply with federal laws protecting historic structures along Church Street. Preservationists are opposed to the entire plan, citing its effects on historic homes and live oak trees that line 61 in the center of town.

Widening 61 is among the final items left over from the 1987 Four-Lane Highway Program, a multibillion-dollar effort to upgrade state highways. Much of 61 through Mississippi is already four-laned, except for Port Gibson and a stretch between the Yazoo River bridge and Leland.