The state Department of Transportation is preparing to open bids for a long-delayed $4.2 million project that will widen South Columbia Street in Chapel Hill, lining both sides with sidewalks and bike lanes from Purefoy Road to Manning Drive.

The two-year project will disrupt traffic. DOT engineers will convert Columbia into a one-way street, northbound from Fordham Boulevard toward Manning Drive, from April through September 2013. Outbound traffic will be detoured onto Manning Drive.

The winding, tree-shaded street will still have just one through lane for cars in each direction after the work is finished in December 2014. But a center turn lane will be added to relieve the frequent backups caused when drivers have to wait for an opening to turn left onto a side street.

It will have five-foot-wide sidewalks on both sides, with bike lanes four feet wide on the east side and five feet wide on the west side.

“This makes it safer for everybody,” said Kevin Moore, a DOT project design engineer. “Right now, pedestrians are just walking along the shoulder of the road, and bicycles are mixed in with the traffic.”

Contract bids are to be opened Oct. 16. Work could start by the end of November.

Lined by leafy residential neighborhoods, South Columbia is a busy path for commuters, students, buses and ambulances. It connects UNC Hospitals with Fordham Boulevard, the N.C. 54 and U.S. 15-501 bypass.

Chapel Hill residents and officials with the University of North Carolina at Chapel Hill have sought improvements to South Columbia since 1997, when the town cited it as a top priority for state funding. The town rebuffed DOT’s original proposal to turn Columbia into a five-lane street.

Siceloff: 919-829-4527 or blogs.newsobserver.com/crosstown or twitter.com/Road_Worrier/