The Minister for Transport, Mr Brennan, has acknowledged that plans for full random breath-testing may not be in place in time for the Christmas period because of legal problems with the legislation.
He also said the roll-out of hundreds of speed cameras around the country has been held up by legal issues.
Mr Brennan said legislation for the two measures, seen as key elements in tackling road deaths, may not be ready to be included in the current road traffic Bill, which he hoped would be passed before Christmas.
Both pieces of legislation had encountered legal difficulties, he said, although he had been informed by the Attorney General that his office was now confident of overcoming the problems.
Problems relating to random breath-testing centre around the issue of the constitutional rights of the individual, and the Attorney General's office is currently drawing up various provisions to ensure personal constitutional rights.
Plans for speed cameras have also encountered difficulties because they involve the transfer of Garda powers to a new private company, which would operate the system.
"The Attorney General's office is working on both, and they have told me that 80 per cent of the legislation has been completed," he said.
"If they are finished by October, then I will put it in the road traffic Bill." Mr Brennan also denied that he had accused gardaí of failing to enforce the current penalty points system when he said they were concentrating anti-speeding measures on "easy targets" on motorways.
"In fairness, they've given 170,000 people penalty points," he said.
"The point I was trying to make is that only 3 per cent of road deaths took place on motorways."
He said he would be asking Garda authorities to concentrate traffic enforcement efforts on weekend nights on country roads, where a third of road fatalities are now taking place.
He is to raise the issue at a crisis meeting on road fatalities which is to take place next Monday.
The meeting also will be attended by the Minister for Justice, Mr McDowell; senior gardaí, including the Garda Commissioner, Mr Noel Conroy; representatives of the National Roads Authority; and the National Safety Council.
The meeting was called following a major rise in road fatalities this year, with 275 people killed between January 1st and last Thursday, compared with 274 for the same period last year.
Mr Brennan said he now expected the penalty points system to be fully computerised by December, after he was informed this weekend that a trial run of the system over the summer had proved successful.
The computerisation is expected to dramatically reduce the amount of paper work in issuing points.
Mr Brennan also maintained the system had been successful.
"In the 22 months since penalty points have been in operation, there have been 122 fewer road deaths, if you compare it with the previous period. 2003 was the lowest year on record for road accidents for 40 years. Based on the statistics so far, this year will be the second lowest."
Mr Brennan was accused yesterday of trying to shift the blame on road deaths onto the Garda during a weekend newspaper interview when he said he was "browned off" about the delays in the introduction of the computer system.
Labour's transport spokewoman, Ms Róisín Shortall, claimed the minister was "in fear of losing his job" in the forthcoming Cabinet reshuffle and was "looking for headlines".