An HGV driver who killed a schoolboy and a mother "unleashed a 19.2-tonne battering ram" when he used his mobile phone at the wheel, a court has heard.
Preston Crown Court heard James Majury, 33, of Coppull, Chorley, opened apps during his journey, including Facebook and a game, and sent texts.
The court heard he was on Facebook a minute before ploughing into a minibus on the M58 in Bickerstaffe, Lancashire.
He has previously admitted two counts of causing death by dangerous driving.
Joe Cairns, 14, from Radcliffe, Greater Manchester, and school support worker Anne Kerr, 50, from Southport, died at the scene on 8 January.
Five other people were seriously injured in the multi-vehicle crash close.
The court heard Majury accessed Facebook less than a minute before his Mercedes Arocs vehicle, laden with scaffolding, smashed into the back of a nine-seater minibus carrying pupils and staff from Pontville School, a special educational needs facility in Ormskirk.
Majury slammed on his brakes just half a second before the crash, the court was told.
"The defendant had been more engaged with Facebook than the road ahead," Francis McEntee, prosecuting, said.
"He had effectively unleashed a 19.2-tonne battering ram on the M58 with devastating effect on the lives of his victims."
'Lapse of judgment'
Majury remained at the scene following the crash and tried to help free the injured from the minibus, but also attempted to minimise his culpability, Mr McEntee said.
"He attributed the collision to a momentary lapse of judgment and told one person 'I took my eyes off the road for a second'," the prosecutor said.
Majury maintained that in a later statement to the police but gave no comment after the findings of an examination of his mobile phone and the lorry's tachograph, the court was told.
During his journey from work about 30 minutes before the crash, Majury unlocked his phone with a six-digit pin on the M6 and texted his mother.
He then launched the Hustle Castle strategy game app, said Mr McEntee.
He had a six-minute hands-free phone conversation with his partner before sending another message to his mother and opening Facebook a minute before the fatal crash.
He is due to be sentenced on Friday.