Tolls on the M1 motorway will drop 10c from midnight tonight after the High Court ruled the company operating the toll has been overcharging drivers since January.
Mr Justice Peter Kelly ruled that Celtic Roads Group (Dundalk) Ltd had misinterpreted the by laws for the calculation of tolls.
The NRA claimed Celtic Roads Group (Dundalk) Limited had been overcharging drivers since 1 January 2011.
The authority said that the company did not interpret the relevant by laws correctly and stood to make €26,000 a week or €1.39m a year by overcharging motorists.
The NRA said the toll should have been reduced on 1 January this year from €1.90 to €1.80 per car because the Consumer Price Index, which is used to calculate the toll, had fallen in August 2009.
The company had claimed the regulation was obscure and its effect absurd.
It claimed that it had a legitimate expectation that tolls would only ever go up and pointed to what it claimed was a promise by former Transport Minister Noel Dempsey to that effect.
However, Mr Justice Peter Kelly said he could find nothing in the regulation to suggest its intention was that tolls would only ever rise.
In drafting the by laws 'simplicity of computation appeared not to have counted for much in the minds of the NRA', no criticism could be made concerning the plain meaning of the regulation.
In his view the NRA was correct in its complaint that Celtic was unlawfully charging tolls in excess of what it was authorised to charge.
The court has heard that there is no way of repaying motorists who have been overcharged.
The case has implications for other toll roads, as the operators of the M4 toll road, the M8 and N25 roads also refused to lower their prices.
Mr Justice Peter Kelly said in light of his decision in favour of the NRA the overcharging should 'cease forthwith.'
Lawyers for the company indicated that tolls would be reduced from midnight tonight in accordance with the judgment.
The company will however take time to consider the judgment before deciding if it is to appeal. The court agreed to place a stay on costs pending that decision.
The Minister for Transport Leo Varadkar has said he has welcomed the clarity provided to the NRA by the Commercial Court.
Minister Varadkar has said that he 'welcomed the fact that the operator of the M1 toll has given a commitment that tolls will reduced from midnight tonight. This is good news for motorists and consumers as well as common sense.'
The Minister also noted that three other tolls, 'the N25 Waterford City Bypass, the M4/M6 Kilkcock Kinnead and the M8 Rathcormac/Fermoy have also been impacted by this court ruling and that the NRA will write to these operators immediately seeking a reduction in these tolls also.'
