The state department began the $11.2 million project, which was awarded to C.W. Matthews of Marietta, in April.
When construction is complete, Canton Road will have two lanes in each direction and six-foot-wide sidewalks on each side.
Underneath the bridge, Cobb Parkway will be widened and gain five-foot-wide sidewalks.
Currently, traffic over the bridge is limited to one direction at a time. When the railroad bridge is complete, the roadway bridge will be closed so the tracks can be shifted over.
McKinnon said the department has not determined when it will close the road bridge but will give the public a two- to three-week notice before it happens.
He said the roadway bridge will be closed for about 45 days and that lane closures on Cobb Parkway will occur during various stages of the construction, but the roadway will never be closed completely.
Cobb County Commissioner JoAnn Birrell, who represents northeast Cobb, urges patience while the closures and detours are in place.
“You’re always going to get someone who’s not quite satisfied, and it is very trying during the construction and with the delays and closures,” she said. “If folks could be a little understanding and patient, it’s all good for the best in the end.”
In the meantime, drivers can use the Canton Road Connector just north of the bridge on Cobb Parkway to avoid the construction area.