Leon David Stott, 34, of St David's Road, Leyland, has admitted causing death by dangerous driving and two counts of causing serious injury by dangerous driving.
Margaret Harrison, 91, died following an accident involving a Mercedes Rigid HGV driven by Stott on January 8 last year on the M58 at Skelmersdale, and victims David Collier and Craig Howroyd suffered injuries.
The accident happened in queuing traffic which built up after an earlier tragic crash in which 14-year-old boy, Joe Cairns, from Radcliffe, near Bury, and his 50-year-old teacher Ann Kerr also died.
Judge Simon Medland QC ordered a pre sentence report and granted bail. He imposed an interim disqualification.
The case was adjourned to September 24 for sentence.
Judge Medland warned an immediate custodial term was likely and offered the defendant an electronically monitored curfew, the days of which would count towards his eventual sentence.