Heavy rain and water on the road led to the deaths of two teenage girls in the valleys, an inquest has heard.
Rhiannon Davies, 18, and Jade Emanuel, 17, both of Rhondda, died minutes after setting out on a Saturday afternoon shopping trip in March 2008.
The car they were in lost control on the A465 heads of the valleys road near Merthyr in heavy rain and was in a head-on collision.
An inquest into their deaths resumes on Thursday.
Rhiannon, from Treherbert and Jade, from the neighbouring village of Blaencwm, were on their way to Merthyr Tydfil when it is thought Rhiannon lost control of her blue MG Rover ZR.
On Wednesday an inquest in Aberdare heard how large amounts of water were present on the A465 at the time of the accident.
The coroner was told that the car carrying the teenagers was travelling on the road between Hirwaun and Merthyr Tydfil on Saturday 29 March 2008.
'Like a waterfall'
Ms Davies pulled out into the middle lane to overtake before the back of the car 'snaked one way, then another', then hit a vehicle coming in the other direction.
Both teenagers, who were not wearing seatbelts at the time, were thrown from the car and died at the scene.
The coroner was told that water had been coming over an embankment "like a waterfall" and running down the carriageway like a stream.
One witness described water after the accident as "running over the top of his shoe".
Motorists who regularly use that stretch of the A465 said it was a common problem and they slowed down because they knew the water would be there in heavy rainfall.
One driver said she had previously aqua-planed on that section of the road.
A doctor who attended the scene said it was an area known to emergency services as a danger area for driving and that he had attended a similar but non-fatal accident two months before the tragedy.
The inquest heard that work had been done on the A465 and that water no longer caused the same problems.
The inquest resumes on Thursday morning.