Mr McGrath has come under sustained criticism for his comments, which have also been reported on the Guardian newspaper website in Britain.
Speaking on Lunchtime with Eamon Keane on Newstalk, Mr Ó Cuív said all the evidence points to alcohol leading to an impairment of driving.
“As far as I understand, all of the empirical evidence shows that as you take a drink and then a second drink and so on that it does impair your judgment and I think people have tried people with cones and they thought they were dead sober and they started knocking the cones after a drink or two,” he said.
However, Mr Ó Cuív did agree there was a misunderstanding by urban people of rural issues.
“The second thing is I do think, that said that there is a slight misunderstanding about rural issues here by urban people who haven’t experienced the challenge of how you get home from an area with no public transport and for this reason, and I’ve discussed this with Noel Dempsey, I believe we need to look at this in the round, and if you took all of the night time transport, or all of the after 8.00pm transport away in the urban areas and said to people ‘well now, the drink-driving law is 50’ I think you would get outrage,” he said.
The rural affairs minister said the proposed 50mg limit was a Government decision and the evidence was that it would save lives.
Meanwhile, an AA survey has shown that almost 64% of people approve of the reduction, an increase of almost 3% on last year.
AA director of policy Conor Faughnan said the figures showed there was very little evidence of an urban/rural divide on the issue.
Support was found to be strongest in Dublin at 66.3%, while it was weakest in Cork where approval for the reduction was 58.1%.
Women were found to be more in favour of the reduction than men.
Meanwhile, more than 500 people were arrested over the bank holiday weekend for suspected drink driving offences, a figure slightly down on last year.