A truck driver who was under the influence of drugs when he fatally ploughed into a group of cyclists at Port Pirie has been sentenced to almost five years' jail.

Sean Anthony Daley, 49, was behind the wheel of a truck which killed a 61-year-old man and injured two others on Germein Road at Solomontown in March last year.

The truck driver of 25 years pleaded guilty to aggravated charges of causing death and serious harm by dangerous driving.

Judge Gordon Barrett sentenced Daley to four years and 11 months' jail with a non-parole period of three years and 11 months.

The court heard a police officer was travelling in the opposite direction just before the crash and saw in the collision in their rear-vision mirror.

"It is plain that you simply never saw the cyclists you were approaching," Judge Barrett said.

Daley stopped after the crash and returned a positive reading to methylamphetamine and cannabis when his blood was tested about an hour later.

The court heard Daley has also pleaded guilty to five offences relating to falsifying work records, working beyond the maximum permissible hours and not resting appropriately between drives.

Company had two sets of drivers' records

As a result of the collision, authorities conducted an audit of his employer Dennis Transport's records, finding that over 41 days 15 drivers had committed 94 breaches of legislation regulating the use of heavy vehicles.

The court heard Dennis Transport kept two sets of wage records, one which recorded the driving which employees were paid and the other a falsified version to conform with the hours they should have been driving.

"I can accept that your employer made you drive excessive hours without sufficient rest and that as a result you were liable to become fatigued while driving," Judge Barrett said.

The company was fined more than $5,000 for the breaches.

The court heard a car driving behind Darley on the day of the crash observed him veering onto the wrong side of the road several times and reported it to police.

But, by the time a patrol was sent from Port Pirie to intercept him, it was too late.

"All of this makes the pain and hurt of the victims of your driving so much worse," Judge Barrett said.

"The public at large was put in great danger but the three victims of this collision have ended up paying the price."

Jail won't bring anyone back

Loved ones of the victims attended the sentencing.

In a statement they said it was "something that they will have to attempt to live with for the rest of their lives".

"No amount of jail time will bring anyone back, or bring any sense of normality back to the lives of the victims and their loved ones," they said.

"We sincerely hope that the sentence handed down will be a deterrent to others who willingly choose to put other people's lives at risk by the selfish act of taking drugs and operating a vehicle on public roads.

"The pain and suffering that we have been through and continue to endure is something that we don't wish upon anyone."

The court heard if it were not for Daley's guilty pleas he would have been sentenced to seven years' jail.

He was disqualified from holding a driver's licence for 11 years.