The 79-year-old great-grandfather was stabbed on the A24 in Findon, West Sussex, after a minor collision with another vehicle on Thursday evening.
Matthew Daley, 34, of St Elmo Road, Worthing, was remanded in custody by Crawley magistrates until Tuesday, when he is due before Hove Crown Court.
He is also accused of possessing a knife in a public place.
The family of Mr Lock, who died as a result of stab wounds, have described him as "gentle, kind and loving".
The retired solicitor had recently celebrated his 55th wedding anniversary with his wife Maureen and had also been given the all-clear from cancer.
A man has appeared in court charged with the murder of pensioner Donald Lock in an alleged "road-rage" attack.