The median sentences for incest, sexual penetration of a child and trafficking a commercial quantity of drugs could all more than double.

The Sentencing Advisory Council today released its report on the practical workings of the state government's new baseline, or intended median, sentencing legislation, and found it could increase the median of some sentences by as much as seven years.

Looking at the median from the five years  to June 2013, the median sentence for incest of three years would more than double to meet the new legislative baseline of 10 years, the council reported.

The council arbitrarily chose five-year medians because the legislation is silent on the issue.  The courts will ultimately decide, which is one of the reasons that predicting the practical application of the laws was difficult, said chairman, Professor Arie Freiberg.

The courts have also been left to work out how multiple baseline offences would affect a final sentence and issues relating to how multiple sentences would be served.

"Baseline sentencing is complex and it will be a challenge for the courts and legal profession to implement," Professor Freiberg said. "I hope this report gives all stakeholders in the criminal justice system the information they need to understand some of the issues and deal with the challenges involved with baseline sentences."

Using the council's methodology, the offence of sexually penetrating a child under 12 years has a median of three years but would shoot up by seven years to meet the new baseline of 10. The baseline for trafficking a commercial quantity of a drug of dependence would increase from 6 years to 14.

Under the new regime, the outcome may have been different for a man who was sentenced on Wednesday for killing three people while driving more than 40 kilometres above the limit and high on the drug ice, in January.

Nei Lima Da Costa was sentenced to 16 years, with a non-parole period of 11, after pleading guilty to three counts of culpable driving causing death, three of negligently causing serious injury and one of recklessly endangering life.

His sentence would have been at the top end of the scale regardless of the new  framework, but under the changes, the new baseline sentence for culpable driving causing death is nine years, compared to the current median of five.

The new sentencing regime is not expected to be felt in the courts for months, as only offences committed after the legislation comes into effect will be subject to the new statutory baselines.

Then it would be years before the new medians begin to stabilise, Professor Freiberg said. "This report has demonstrated how the median sentence for an offence will vary according to the period analysed, based on the number of charges of that offence sentenced each year," he said.

The laws, known as the Sentencing Amendment (Baseline Sentences) Act, were passed by State Parliament in August.

Professor Freiberg described them as "a major change in sentencing methodology". "If the median is in conflict with current sentencing practices, then the court has to have regard to the median and not the current sentencing practices."