Ditches which should have prevented water running off fields onto a road where two teenagers died were blocked, an inquest has heard.
The blockages allowed a stream of water to run on the A465 Heads of the Valleys road where Rhiannon Davies, 18, and Jade Emanuel, 17, died.
Their car was involved in a head-on crash in heavy rain in March 2008.
The Aberdare inquest was told that the drains were likely never to have been inspected. The hearing continues.
An area engineer from the South Wales Trunk Roads Agency told the inquest that investigations following the collision found blockages in the drainage system.
Rhiannon, from Treherbert, and Jade, from the neighbouring village of Blaencwm, were on their way to Merthyr Tydfil for a shopping trip when it is thought Rhiannon lost control of her blue MG Rover ZR.
The car hit another vehicle travelling in the other direction between Hirwaun and Merthyr.
The inquest heard that the ditch and drainage system at the side of the road had become silted up and shallow, with rocks and grass in one part of the drain.
David Chan, the area engineer responsible for that section of road, admitted it was likely that this meant the ditch never had been inspected.
Robert Twigg, who regularly patrolled that section of road for the agency, told the inquest that he had been aware of a problem on the other side of the road which had been fixed.
But he said the first time he noticed water on the direction travelling east was when he attended a similar but non fatal accident two months earlier.
He said on that occasion he had used his shovel to clear debris from the entrance to the drain and suggested to his superiors that the ditch should be made deeper.
Days before this crash he cleared debris from the drain again after it had become clogged with tree cuttings.
The inquest has heard that since 2008 work has been done to the ditch and drains and water is no longer a problem there.
The inquest was previously told that water had been coming over an embankment "like a waterfall" and running down the carriageway like a stream.
The hearing continues.