A motorist made a "monumental error" by taking a wrong turn in fog on to a dual carriageway, causing a fatal head-on crash, a jury heard.
The front-seat passenger in the other car – James Richmond, of Groby – died at the scene, on the A46 in Six Hills.
Three other people in the same car, a Mazda MX3, were injured.
David Driver (30) denies causing 44-year-old Mr Richmond's death by driving dangerously in his Audi A3 as he headed south on the northbound carriageway, at 5.10am on March 16 last year.
Michael Auty, prosecuting at Leicester Crown Court, said Driver, who had been working in Melton, was going home to Rotherham with his brother when they joined the A46 at the Dalby interchange.
He said rather than filtering on to the northbound carriageway, as indicated by two turn left signs, Driver went past two no entry signs, down the wrong slip road.
"He crossed into lane two, nearest the central reservation," said Mr Auty.
It was dark and there was patchy fog, but Driver continued for half a mile, allegedly narrowly missing an oncoming lorry and a van, the court was told.
"He made a monumental error of judgement," said Mr Auty.
Mazda driver Slawomir Korzekwa said in a statement that he was travelling north at about 70mph.
"I suddenly saw bright lights coming towards us and couldn't make out what it was or why lights were facing me," he said.
"A car was coming towards us in the wrong direction. When I realised what it was, I braked heavily.
"I managed to steer right and the next thing I remember was my car was upside down."
Two other cars, also heading north, clipped the upturned Mazda.
Lorry driver Andrew Brown told the jury he encountered the Audi shortly before the collision with the Mazda.
He was moving into the second lane heading north, at about 50mph, when he was forced to pull back into the first lane to avoid the defendant.
Mr Brown said he could see illumination from a satellite navigation system in the Audi and said the driver appeared "utterly oblivious to the reality of the situation".
He alerted the police, but a short while later heard on the radio news there had been a collision.
A motorist heading south on the correct carriageway tried to get Driver's attention, to no avail, it was claimed.
At the scene, Driver, of Pottery Lane, Rawmarsh, Rotherham, told police he was following his sat nav system.
In interview, he claimed it was "thick fog" and he was unfamiliar with the road.
Mr Auty said: "The defendant said his brother said he thought they had turned down the slip road the wrong way."
Driver claimed he encountered no other vehicles prior to the collision.
Later, he said he had not seen any no entry road signs.
Mr Auty said: "A sat nav system cannot be, and isn't, a substitute for common sense and using your eyes."
The trial continues.
