A young woman accused of death by careless driving was not called as a witness in Lewes Crown Court today after suffering brain damage in the collision.
Amie Gatland, 21, was driving her BMW along the A281 past Cowfold when she swerved into the path of a Volkswagen Polo, killing her own passenger Charles Andrews, 21.
Forensic scientist Peter Davey showed the jury photographs of the collision site which involved Harriet Burrage, 22.
Miss Burrage was left with a broken wrist, bruising and whiplash while Amie contracted memory loss.
A series of possible reasons for the accident was given by Mr Davey, who has a PhD in Forensic Road Collisions.
He said that water damage may have caused the areas of fretting on the road, which he described to mean erosion or sinking of the road surface.
Analysis carried out in 2012 and 2013 by Alexandra Luck, an expert in construction and speed resistance, found that the road should have been treated for poor resistance levels.
The jury heard that the accident site had been the location of 15 driving incidents since 2006, with seven of those being since 2013.
Both women had been driving within the speed limit, and were tested on the scene for alcohol or substances, with clean results according to Mr Davey.
A statement from Miss Burrage confirmed that Miss Gatland, who gave a not guilty plea, was not distracted and did not deliberately cause the accident.
Although both cars were in too much of a wreck to test, neither cars were found to be defective.
The trial continues.