It also flies in the face of the board's previously stated explicit opposition to building major commercial schemes alongside motorways.

Last October, the chairman of ABP John O'Connor seemed to signal that the days of building hotels, business parks and retail warehousing at motorway interchanges were numbered. Such schemes were "piggybacking" on new roads with local traffic "weaving on and off over short distances" to get access and running into conflict with long distance traffic. This affected the capacity of roads and raised safety concerns, he declared.

O'Connor specifically cited the M50 as an "extreme example" of piggy-backing commercial developments and said that such schemes would face a "high hurdle" in winning board approval. He added that the board would be taking heed of the National Roads Authority's (NRA) arguments against this type of development.

Perhaps most importantly of all, O'Connor concluded that the huge multibillion euro investment in roads would have to be written off in 10 years unless local authorities stopped granting permission for such schemes.

Fine words indeed, but following last week's decision on Ikea, it's impossible to avoid the conclusion that the board talked the talk on motorway developments, but failed to walk the walk.

Once the NRA, the state agency responsible for our national road network, objected to the Ikea development, a decision to turn down planning permission should have been an absolute no-brainer.

The NRA didn't pull any punches about the proposed superstore and the impact it would have on the M50, already Ireland's busiest motorway. It said the Ballymun store would result in "significant delays and congestion" on the M50 and would "significantly undermine and negate the benefits" of the 1bn upgrade of the ring-road.

The delays and congestion caused by the Ikea development would be "unacceptable on this section of the motorway, which forms part of the most critical artery for traffic distribution around Dublin and which serves as a vital link to Dublin Airport and Dublin Port, " the NRA said, adding that the Ballymun junction of the M50, even after it is upgraded, "will be unable to cater for the predicted future traffic levels."

Given the bluntness of the comments from the one body we should be listening to most of all, that should have been that. Instead permission has been granted, albeit with a whole series of conditions which themselves surely point to serious reservations on behalf of ABP.

You have to question whether a store that isn't being allowed to open until 11am or close before 10pm, for traffic reasons, should be allowed open at all on that particular site? The 11am opening will undoubtedly mean the store won't add to the morning gridlock on the road, but it's the weekend where the real impact of the store on traffic on the M50 is really likely to be felt. Traffic jams on a Saturday and Sunday are already a regular occurrence on the road and the presence of three major shopping centres along the motorway is unquestionably a factor in that. A report commissioned by the Irish Hardware and Building Materials Association claimed that the Ikea store could generate 7,000 to 10,000 extra car trips a day on the motorway at the weekend. Nor should the impact of the extra traffic on Ballymun itself be forgotten.

The other conditions applied are undoubtedly well-meaning, but it's difficult to see what impact they will really have.

How, for example, will a shuttle bus to and from Ballymun help to significantly reduce traffic levels?

The two main arguments put forward by advocates of granting planning permission to Ikea are the numbers of jobs it brings to Ballymun and the downward pressure the increased competition will have on furniture prices. Nobody for a second doubts the amazing work being done in regenerating Ballymun but to focus on the need to bring jobs to the area completely ignores the fact that Ballymun is just three miles from Dublin city centre and well served by public transport. We are not talking about a town in the middle of nowhere, during an economic recession. What next . . . an advance factory for Phibsborough?

There is no question that the arrival in Ireland of Ikea . . . a fine retailer selling at very competitive prices . . . will be welcome news for consumers. But that isn't a reason to abandon good planning principles. In the UK for example, after being refused planning permission by the British government for a new out-oftown shop near Manchester, Ikea announced that it was planning to build smaller, city-centre shops . . . a quarter of the size of the company's usual outlets.

Why couldn't that have happened here?

The real damage, of course, was done in 2004 when the government sacrificed its own well-thought out planning guidelines which had restricted the size of retail warehouses. The government said at the time that the rules were being changed, not to suit one company, but for designated regeneration areas. But, of course, the reality was that it was accommodating Ikea. Given that decision, perhaps it was unfair to expect An Bord Pleanala to restore some faith in our imperfect planning system but that doesn't make last week's decision any less disappointing.

It's hard to shake the feeling that the last chance to save the M50 and Ballymun from further traffic chaos has been lost.