Emergency services were called to the junction of the A264 and A24 northbound at Broadbridge Heath after a car left the slip road carriageway at about 7.45pm on Sunday, April 17.
A police spokesperson said: “The incident involved a single vehicle, a silver Peugeot 208.
“Tragically, an 80-year-old man from Peaslake, Surrey, was pronounced dead at the scene. His next of kin have been informed.
“A 69-year-old woman sustained life-threatening injuries and remains at the Royal Sussex County Hospital in a critical but stable condition.
“Anyone who witnessed the incident or who has footage of the Peugeot in the minutes before the incident is asked to email: [email protected] and quote Operation Linford.”