Traffic on Interstate 81 South in Montgomery County will be down to one lane starting at 8 p.m. Thursday night.

The lane closure is expected to be in place until 6 a.m. Friday morning. Rolling roadblocks may also be put in place overnight.

The work is needed while the Virginia Department of Transportation builds a truck climbing lane between mile markers 120 and 125. Thursday’s overnight lane closure is needed so crews can put in a new traffic pattern in place at the top of Christiansburg Mountain.

Starting Friday, VDOT asks drivers to pay attention to pavement markings and signs at the beginning of the new three-lane section of road because traffic patterns will change.

The truck climbing lane project is expected to be finished in November 2013.