A man has died and another is fighting for his life following a crash on the A12 near Boreham on Monday night.
A 36-year-old man from Woolwich died at the scene and a 24-year-old, from Bexley, remains in a life-threatening condition after being taken to hospital by air ambulance.
A 31-year-old man, from Belvedere in Kent, has been arrested on suspicion of causing the death while dangerous driving and being unfit through drugs.
He remains in custody for questioning.
Essex Police said it believed a car had collided with two pedestrians on the exit slip road at junction 19 at about 18:30 BST.
Anyone who spotted a Vauxhall Zafira that pulled over on the slip road is urged to contact police.