A man has been seriously injured after he fell from his motorcycle and was hit by a car near the RAF Waddington base at 6.50pm on January 16.
Police say the man, thought to be in his 50s, was riding a blue Honda motorcycle when he turned onto the A15, Sleaford Road, from the viewing area at RAF Waddinton.
After falling from the bike, he was then involved in a collision with a red Ford Mondeo.
The man was taken to Lincoln County Hospital with multiple fractures and is in a serious condition, police said.
Anyone who was in the area and saw the collision or saw the blue Honda motorcycle or the red Mondeo before the collision is asked to contact police on the non-emergency number 101 or the witness hotline 01522 558855.
PC Gareth King is the officer dealing with the incident. The road was closed until just after 10.30pm last night, while a police investigation took place.