Mitchell Ryan Laidlaw, 34, has pleaded guilty to charges of culpable driving causing death and drug-driving following the July 2020 incident that claimed the life of the ACT Senior Australian of the Year.

When Laidlaw appeared in the ACT Supreme Court for the start of his sentencing on Thursday, his mother, Deborah Laidlaw, and partner, Julie Hughes, gave evidence.

Mrs Laidlaw told the court she had often had her "inconsolable" son crying on the phone since the fatal crash.

"He was devastated, as we all were," she said.

"He couldn't believe an accident had happened, couldn't believe such a tragedy had happened."

Ms Hughes added Laidlaw had been in "utter shock" after the incident, which had caused many sleepless nights.

She told the court Laidlaw had lost his roughly $90,000 per year job installing security systems in government buildings because he was facing criminal charges.

This had placed financial strain on their family of five, she said, because he was now earning just $50,000, "if that", as a labourer.

CCTV footage of the Commonwealth Avenue crash was played to the court on Thursday, showing Laidlaw's Nissan Navara rear-ending Ms Salthouse's wheelchair-accessible motorcycle.

According to an agreed statement of facts, Laidlaw was going about 80km/h in a 70km/h zone and did not brake or take evasive action prior to the collision.

Ms Salthouse's three-wheeler vehicle had been travelling at just 42km/h. It was shunted about 170 metres down the road by the impact, striking the median strip on the Commonwealth Avenue Bridge before coming to rest in the left-hand lane.

Laidlaw and several passers-by stopped to help Ms Salthouse, a 71-year-old paraplegic who broke her back in 1995, and the agreed facts say the victim was initially observed to be "calm and jovial".

Her condition deteriorated, however, and she was rushed to Canberra Hospital, where she went into cardiac arrest and died despite "vigorous" attempts at resuscitation.

A subsequent autopsy found her cause of death to be multiple injuries sustained during the crash.

Laidlaw returned a positive result to a roadside drug test and was taken to City Police Station, where a further analysis revealed there was methamphetamine in his system.

He later told police he had taken "three puffs" of methamphetamine at a house party three days before the crash.

Prosecutors did not allege he was impaired by the drug or under its influence at the time of the collision, instead relying on his excessive speed and failure to keep a proper watch on the road and surrounding vehicles to prove the culpable driving charge.

On Thursday, ACT deputy director of public prosecutions Anthony Williamson told the court those two factors represented "an unjustifiable and gross departure from the standard of care that a reasonably prudent driver would observe".

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Mr Williamson said it was accepted, however, that this was a case of momentary inattention or misjudgment.

He told the court a suspended jail sentence or intensive correction order would be appropriate.

Laidlaw's barrister, Kieran Ginges, pushed for a suspended sentence.

Mr Ginges told the court the wheelchair-accessible motorcycle had left Ms Salthouse "extremely vulnerable", and that "a confluence of tragic events" had led to her death.

He said if Laidlaw had been travelling within the speed limit or realised just one second earlier that there was a risk of colliding with the 71-year-old's vehicle, "it may have avoided everything".

Chief Justice Lucy McCallum ultimately adjourned the sentence proceedings until May 27, when Ms Salthouse's family will have the opportunity to make victim impact statements.

Laidlaw will remain on bail until then.

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