A motorist was killed after his car smashed into the back of another vehicle, mounted a kerb and hit a tree.
Colin Sharpington, 57, of Grosvenor Gardens, Billericay, was driving a green Vauxhall Omega, in Princes Road, Chelmsford, when the crash happened.
Police said the Vauxhall was involved in an accident with a silver Peugeot 206 in queuing traffic.
Police suspect the Billericay man may have suffered a heart attack.
A police spokeswoman said: "Passers-by went to the aid of the driver of the Vauxhall as soon as it was safe to do so and all three emergency services attended."
James Flynn, duty manager for the East of England Ambulance Service, said calls had been made to the service from both the police and the public.
He added: "The member of the public who made a call said the patient was unconscious.
"The ambulance was there for about 16 minutes before they took a man to hospital."
The ambulance arrived at the scene at 6.15pm on Friday before taking the driver to Broomfield Hospital in Chelmsford, where they confirmed he had died.
Anyone with information is urged to Chelmsford road police on 01245 240625.
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