New powers to crack down on drink and drug-driving in Ireland will be rigorously enforced, Garda chief Noirin O'Sullivan has warned.
Blood samples can be taken from incapacitated or unconscious drivers without their consent, under laws which come into effect today.
Under the procedure, the driver will be asked to consent to the sample being tested once he or she is in a fit state to respond.
But they will be guilty of an offence if they refuse.
The Government said the new rule closed a loophole, ensuring all drivers involved in serious collisions would be tested for drink or drugs, and would act as a deterrent.
Gardai also have new powers to test motorists they suspect of being under the influence of drugs.
These include asking a driver to walk in a straight line, turn around, stand on one leg and touch their nose with their finger.
They can also take evidence about a suspect's pupil dilation.
Garda Commissioner Ms O'Sullivan said the tests would save lives.
"Over the last decade, we have seen that similar measures such as reducing the alcohol limit and the introduction of penalty points have helped reduce the number of road deaths," she said.
"We believe these new regulations will do the same and we will be rigorously enforcing them."
The new regulations come under the Road Traffic Act 2014.
Professor Denis Cusack, of the Medical Bureau for Road Safety, said 10,500 blood and urine tests were carried out in Ireland over a five-year period up to last year.
Of these, almost 7,200 tested positive for drugs, rather than alcohol.
Cannabis, followed by benzodiazepines were the most prevalent drugs detected.
"If you are taking medicines under the direction of your doctor or pharmacist and you heed their advice in relation to driving, you should have nothing to fear," he added.
Liz O'Donnell, chairwoman of the Road Safety Authority, said: "Up to now, the research is that many drug-drivers see little risk of apprehension.
"They can actually delude themselves to be better drivers while under the influence of drugs and imagine themselves at low risk of collision."
Road deaths have increased in Ireland over last two years after several years of decline.
Some 179 people have been killed on the roads already this year compared to 172 deaths over the same period last year.
Some 4,500 gardai have been trained for the powers handed to the force under the new road traffic legislation.
A Garda spokesman said: "This includes the provision to request a designated doctor to take a blood specimen from an incapacitated person following a road traffic collision. The training of further Garda personnel in this area is ongoing."
The Irish Council for Civil Liberties (ICCL) said any significant changes in the law should be reflected in human rights based training.
"The ICCL's Director, Mark Kelly, represents the Council on the Garda Commissioner's Strategic Human Rights Advisory Committee (SHRAC) and, in that capacity, takes a close interest in the quality of training being provided to An Garda Siochana on a broad range of human rights-related issues, including the treatment of vulnerable suspects," an ICCL spokesman said.
"Any significant changes in law and practice should be reflected in human rights based training and this is a matter that the ICCL keeps under constant review, including through its membership of SHRAC".