A highway patrolman has admitted writing fake traffic infringements for non-existent drivers.

Leading Senior Constable Stephen Alan Saltmarsh wrote the tickets, supposedly following traffic stops on the Hume Highway at Gundagai between May and July 2015.

The 39-year-old highway patrolman pleaded guilty to 18 charges of unlawfully modifying the restricted police database, and three counts of knowingly making a false statement.

Facts tendered to Wagga Local Court showed Senior Constable Saltmarsh used the Police COPS database to enter infringements against drivers purportedly from the UK, Thailand, Germany, USA and China.

It later emerged there was no record of such people entering Australia, and their ACT numberplates had never existed or did not match the type of vehicle described.

"The accused expressed remorse during the [police interview]," facts tendered to the court stated.

"He stated he knew what he was doing was wrong, but was unaware that the creation of the reports or submission of the infringement notices and defect notices was a criminal offence," the facts said.

The infringements included minor defects, speeding and seatbelt offences, driving in the wrong lane and inappropriate use of high beam lights.

The Police Professional Standards Command started Strike Force Stonegarth to investigate, after the State Debt Recovery Office raised concerns about the fines, including that there was no in-car video evidence provided for roadside stops associated with the tickets.

The court was told the police database login screen displayed a warning that improper use could result in fines or jail.

A NSW Police Force spokesman said Senior Constable Saltmarsh was currently suspended from duty, but continued to receive pay.

He is due back in court for sentencing in March.