Valuer John Morley, a director of estate agents Hamilton Osborne King, told the arbitration hearing into the disputed €47 million claim that equivalent lands in neighbouring Foxrock were worth €600,000 per acre.
He had deducted €150,000 per acre for the Jackson Way lands because they did not have adequate road access and they might have had to acquire extra land to link with the nearest main road. At €450,000 per acre, the total value of the 106 acre site came to just over €47m.
Under cross examination Mr Morley agreed he had based his valuation on the opinion of another Jackson Way witness, planning consultant Tom Phillips. Mr Phillips gave evidence the lands would have been rezoned as residential had it not been for the motorway.
He said it was normal to value lands based on their development potential rather than to stick strictly to the existing zoning. In Jackson Way's case the existing zoning was mainly agricultural, with a small portion of industrial, both worth a great deal less than residential land.
Mr Morley added, however, that even if the land had not been rezoned, it still would have suffered a "massive devaluation" because the motorway cut the property in two.
It is believed Dun Laoghaire-Rathdown County Council has offered no more than 10m in compensation.
Dermot Flanagan SC, counsel for the county council, questioned whether Mr Morley was too optimistic in expecting Jackson Way could have arranged for road access by themselves.
He said every landowner along a two mile stretch - including a number of people who lived on the land - would have had to agree with construction of a link road to Jackson Way's site, and this was far from certain. The motorway, on the other hand, had been planned and executed by the State and a link road provided that opened up access to the Jackson Way lands.
Mr Morley argued getting such agreement from adjoining landowners would not have been a problem as improved road access would have served everyone's interest. He admitted, however, that when the county council moved onto the site in mid-2000, no such approaches had been made.