The deal will cost the state in excess of Euro600m but motorists will still have to pay to use the road under a new electronic system of barrier free or 'free flow' tolling.

However, the government will argue that the revenue raised will be put back into the roads programme.

The toll bridge, which is used by 95,000 vehicles every day, is blamed for the major traffic congestion on the M50 although NTR insists that the problems are to do with design and the interconnecting junctions, which are currently being addressed in a major upgrade of the motorway.

Negotiations on the buyout have been underway since mid-2006. The talks had stalled over the issues of taxes and the length of payments, but Taoiseach Bertie Ahern signalled last month that he wanted the deal to be concluded quickly. Government sources said this weekend that contacts were ongoing between the two sides and agreement was near.

NTR is seeking a deal in which it will pay 12.5% corporation tax on the purchase price rather than the higher 20% capital gain rate. The two sides have also been in dispute over the timing of the Euro600m-plus payment, with the government looking to stretch it out until the NTR concession on the toll plaza expires in 2020.

The M50 toll bridge was built by NTR and the company operates under an agreement struck in 1987 with former Fianna Fáil minister Padraig Flynn.