The B1191 is closed between Woodhall Spa and Martin after a driver sustained serious injuries in a crash.
A car left the road near Martin South Drove at 9.40am on Wednesday, January 3.
The driver has been taken to the Queen’s Medical Centre in Nottingham with serious injuries.
A Lincolnshire Police spokesperson said: “The collision has happened on the straight stretch of road between Woodhall Spa and Martin.
“We have closed the road to allow an investigation of the scene.
“We anticipate the road will be closed for the next two to three hours.”