Transport Infrastructure Ireland (TII) has said it has “done everything we can do” to alleviate traffic congestion on the M50, with capacity now “beyond Celtic Tiger numbers”.

TII’s director of corporate communications, Sean O’Neill, said investment and redesign to alleviate worsening congestion and commute times has been “maxed out”, and any remedy would have to be decided by the Government.

“We’re actually beyond the Celtic Tiger numbers; we’re at capacity. We can’t make it any wider, and you can’t make it a double-decker,” he told RTÉ’s Prime Time on Tuesday night.

“We’ve added lanes, we’ve elongated merging corridors, which means it gives you safer time and more distance to get into an interchange and out,” he said, noting such interventions have been “maxed out” by TII.

“The upgrade, overall, has been a success, but we’ve done everything we can do and anything additional would have to be a significant policy decision by Government. That wouldn’t be for us to decide,” he said.

The only way capacity can be expanded in the short to medium term is by reconsidering an eastern bypass, according to Aisling Reynolds-Feighan, a professor of transport economics at University College Dublin.

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A circular motorway around Dublin city was first proposed in the 1970s to allow drivers to bypass to the east and west.

The western side of the circle was built in the form of the M50, which was completed in sections, opening from 1990 to 2010.

The eastern side, however, which would have required a tunnel under or bridge over Dublin Bay, never went ahead.

“If we were to complete the ring, it would give an alternate east or west bypass of the city,” Prof Reynolds-Feighan said.

There has been a 17 per cent increase in the population since the M50 was completed in 2010 and that alongside a “very buoyant economy” has fuelled increased volumes of traffic, she said.

Housing shortages, meanwhile, have led to an increase in people commuting to work in Dublin from surrounding counties.

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