SABATTUS — The Maine Turnpike Authority said the highway’s Exit 86 southbound off-ramp will be closed for roughly three weeks starting Monday.

Motorists must use either Exit 102 in West Gardiner or Exit 8 in Lewiston while crews work to make improvements to the ramp’s road surface.

Upgrades to the other three ramps at that exit are in progress, but won’t need to be closed, Turnpike spokeswoman Erin Courtney said Thursday.

“We tried to minimize the effect on the traveling public as much as we possibly could,” she wrote in a news release. “We were able to create temporary travel lanes for the other three on- and off-ramps, but southbound-off was too close to a stream, making a closure of the ramp necessary.”

Message boards are in place and will continue to inform approaching travelers of the closure.

Sensors are being installed in the ramp bed that will enable Turnpike officials to determine the classification of vehicles that exit there, she said.

The Exit 86 ramp work is included as part of a much larger $6.5 million project, awarded to Lane Construction Corp. of Lewiston, Courtney wrote. The project consists of pavement rehabilitation and so-called clearzone improvements from Mile 80.7 in Lewiston to Mile 88.6 in Sabattus. The overall project is scheduled to be completed this fall.