"The drug laws are meant to target people who are taking illicit substances, they were never intended to quantify how affected a person is," Wayne Evans said.

The laws can penalise a person on the basis of any detectable level of a drug, not necessarily an intoxicating level.

Mr Evans said there is a place for drug driving laws in the community, to protect people from drivers who may or may not be affected by drugs but have consumed illicit substances which show up in the testing.

Mr Evans was a Port Macquarie magistrate from 1997 to 2009, a Kempsey and Bellingen magistrate until 2014 and a police prosecutor from 1963 to 1985.

Recently another former NSW magistrate David Heilpern spoke about drug driving laws and told another media outlet that they are ineffective and destructive.

Mr Evans agreed with Mr Heilpern the law does penalise on the basis of any detectable level of a drug, not necessarily an intoxicating level.

However, unlike Mr Heilpern, he said the laws still play a role in helping to protect the community.

"I agree young people take these substances and it might remain in their system sometimes for 14 days," Mr Evans said.

"I would doubt they would be affected by the 14th day.

"But who am I or who are others to say they are not affected on the first, second, third, fourth or fifth day?."

Mr Evans compared this scenario with a campaign by the government which has now proved ineffective when it came to alcohol consumption and level of intoxication.

"They used to say you could have two drinks in the first hour and one every hour there after (to still be under the limit to drive).," he said.

However, Mr Evans said the government realised this was an error because it didn't take into account a number of contextual factors such as body size, metabolism and prior health conditions.

Mr Evans said to get the drug-driving reading a person had to have taken an illegal substance in the first place.

"Why should the community be forced to sit back, watch and be at risk by people who are intent on breaking the law?," he said.

He said the offence is don't drive with the illegal substance in your system, not don't be affected by it.

Mr Evans said if a drug-driving case is connected with serious offence, the matter might be contested and in that case a drug test sample may be subjected to an objective assessment by an expert, such as a pharmacist.

He said magistrates rely on the facts provided to them by the police and take into account the circumstances of the case from when the person was charged.

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