A HGV driver fell asleep at the wheel moments before his vehicle hit a lorry, killing a 72-year-old grandfather, a court has been told.
Timothy Harkness, from Carlisle, died when his lorry crashed with Rhys Gardiner's double-deck trailer on the A66 near Penrith on 3 April 2018.
Carlisle Crown Court heard Mr Gardiner's HGV strayed on to the wrong side of the road when he fell asleep.
The 24-year-old, from Doncaster, denies causing death by dangerous driving.
Prosecutor Tim Evans told the court: "The Crown's case here is perfectly simple and blunt. That this defendant, driving his HGV, fell asleep at the wheel and that's what caused the crash."
The court heard Mr Gardiner had been out socialising during an Easter bank holiday weekend until 03:00 BST on the day before the crash.
He sent a "highly significant" text to his girlfriend at 03:07 BST on the day of the crash which read "Tired lol". He began driving less than 20 minutes later, Mr Evans said.
The court was told tyre marks showed the trailer unit strayed on to a grass verge for more than 100 metres.
Dashcam footage from Mr Gardiner's cab also showed his vehicle "bounce viciously" as it was steered back on to the A66 and into the path of Mr Harkness's lorry.
The court heard that in a first police interview Mr Gardiner spoke of losing traction on the nearside of his vehicle on what he thought was mud.
In a second interview, he admitted being tired when waking up to start work, but denied falling asleep immediately before the crash.
Mr Evans told the jury: "The accident waiting to happen did indeed happen with fatal consequences.
"The defendant must plainly have been very tired. The Crown say you can be entirely confident that falling asleep was exactly what he did.
"Frankly, what other explanation can there be?"
No-one else was hurt in the crash.
The trial continues.