The state Department of Transportation is encouraging motorists to avoid the Hwy. 20 bridge over the Chattahoochee River on Friday night.

One of the bridge’s two lanes will be shut down again from 9 p.m. to 6 a.m. so crews can conduct soil surveys.

Teri Pope, a spokeswoman for the DOT, said the crews  did not finish gathering the samples needed overnight Thursday before they were required to open the lane for morning rush hour Friday.

The engineers hit rock in the river bed that slowed the work, she said. The project began Wednesday night.

The surveys are needed for the final design of a proposed four-lane bridge spanning the river between Forsyth and Gwinnett counties.

“There’s going to be extreme back-up because we’re cutting the capacity of the bridge in half and traffic volumes are high there to start with," Pope said.

“We’re trying to do it overnight to minimize the impact to traffic, but please avoid the area. It’s not going to be pleasant for motorists.”

The bridge is about three quarters of a mile long. Including the $3 million expected for right-of-way costs, the $15.1 million project is slated for construction during the 2015 fiscal year.

Also set for 2015 is the widening of Hwy. 20 to four lanes between James Burgess and Samples roads in east Forsyth.

The 2.75-mile project could cost nearly $22 million. In addition, with 63 parcels needed to complete the project, right-of-way costs are estimated at about $26 million.

Pope said the soil samples being collected as part of the bridge project will help determine the type of footings needed in the final design. 

DOT construction engineer Randall Davis said in a statement that off-duty law enforcement officers would be on the scene to help ease any confusion.

“A flagger will stop traffic on each end of the bridge and motorists must wait their turn to cross,” Davis said. “Please avoid the area if possible. Crews will be working on and under the bridge.”