The crash happened on the slip-road to the A414 at Sandon, Chelmsford, at 03:40 BST on Thursday.
The teenager, from South Woodham Ferrers, had multiple injuries and was taken to Broomfield Hospital in Chelmsford.
He was later transferred to Addenbrooke's Hospital in Cambridge, where he died on Friday night.
An 18-year-old pedestrian died in hospital after he was hit by a van on the A12 in Essex.