The Taoiseach says he has received assurances from the Attorney General that the introduction of random breath testing is "legal and constitutional".
On the first day back after the Christmas recess, Mr Ahern told the Dáil the Cabinet had reached a conclusion on the matter after a long legal debate and intended to introduce the measure in the coming months.
He said that "it will have to be operated in a particular way."
Mr Ahern said the Attorney General's advice had conveyed to the Garda Commissioner Noel Conroy in the last few days.
Earlier Fine Gael leader Enda Kenny said the Government's record in dealing with the carnage on Irish roads has been a "dismal failure".
Mr Kenny said: "The roads of Ireland are littered with monuments to tragic accidents and lost lives".
He said the Government had failed to achieve any of the targets announced in the National Road Safety Strategy.
He said the Minister for Transport Martin Cullen had "failed utterly" in his responsibility to achieve these targets.
Mr Kenny also claimed there was a perception among the Irish public that the penalty points scheme was being used as a money gathering exercise.
Mr Ahern said: "The number of road deaths and the carnage on the roads is disappointing and disturbing."
He said the National Road Strategy target of bringing down annual deaths to 300 will be difficult to achieve.
The penalty points system will be extended from five offences to 35 on April 1st, he said.
Minister for Finance Brian Cowen will announce tomorrow that up to 60 offences will carry on-the-spot fines.
