The new law means that drivers found to have a certain level of heroin, cocaine or cannabis in their blood are guilty of an offence, irrespective of whether there is evidence of their driving skills being impaired.
The Garda can use new swab machines to test for the presence of these illegal drugs if they stop a car which they believe is being driven erratically, and also at random roadside checkpoints. What are now called mandatory alcohol testing checkpoints will be called mandatory intoxicant testing checkpoints.
People whose swabs indicate the presence of the drugs can be arrested and brought to a Garda station for a blood test. The presence of the drugs above the legal limits in the blood will then constitute evidence for any future case.
The blood tests will be able to distinguish between heroin and opiates that might arise in the bloodstream due to the ingestion of prescribed drugs, according to the Department of Transport.
For all other drugs, be they legal or illegal, the position will remain that presence plus impairment to the extent of being unable to control the vehicle, is an offence.
The proposed law comes in the wake of evidence collected by the Medical Bureau for Road Safety which has found a disturbing connection between fatal road incidents and drug use.
Cannabis use
In particular the research has found a strong link with cannabis use.
The research indicates that, across a 10-year period, just under 10 per cent of people who lost their lives in crashes had drugs in their system, and of that 10 per cent of people, between 60 and 70 per cent had cannabis in their system.
Road traffic offences constitute a huge proportion of all charges brought before Irish courts and drink-driving charges are among the most contested.
Minister for Transport Paschal Donohoe has said the proposed new law mirrors one introduced in England and Wales in March of this year and that great care has gone into its preparation.
In England and Wales the banned drugs include LSD as well as heroin, cocaine and cannabis. The proposed Irish legislation, and the swabbing devices that are to be used, can be changed to accommodate the citing of new illegal drugs.
Statistics released in England and Wales earlier this year showed approximately 400 people per month were being arrested under the new drug-driving law, with large variations between police regions.