The Irish Business and Employers' Confederation (IBEC) in the west has thrown its weight behind a campaign to improve the main artery linking Mayo to the east, which is said to be hindering industrial development.
Allergan, one of the county's leading healthcare multinationals, sustained €130,000 in product damage last year due to the state of the N5, according to its director of human resources, Mr Martin Gillen.
Mr Gillen, who is chairman of the Mayo Industries Group, says the Baxter healthcare company experienced losses of €190,000 during last year for the same reason.
Such is the state of the 83-mile route between Westport and Longford, particularly on the stretch between Swinford and Tarmonbarry, that questions are being asked among customers in Japan, Korea and the Middle East, Mr Gillen says.
Allergan makes opthalmological products, along with the Botox treatment - which is better known for its cosmetic applications, but is also producing results in cases of junior cerebral palsy.
"Some companies in Mayo are now using the N4, which is adding to their journey, to avoid product damage," Mr Gillen says. "It is an urgent issue, and one that is having a very negative impact on the image and credibility of Mayo abroad."
Mr John Brennan, regional director of IBEC West, says the subject has been raised at national level with both Government Ministers and the National Roads Authority (NRA). IBEC West is not happy with the NRA's response - a promised basic upgrade of the route over a four-year period.
Such an upgrade, which will cost around €12 million, should take place within two years, and a long-term strategy for a new motorway be devised, according to Mr Gillen.
When it was discussed initially with the NRA early last year, the roads authority agreed to commission a study that would set down the condition of the N5, and the work required to improve it in the short term.
Maps completed for this identified serious problems in relation to archaeological and heritage sites on the Frenchpark-Strokestown section of the route, including Rathcroghan in Co Roscommon.
Given the implications for long-term strategy, IBEC West sought an alternative which would avoid the sensitive areas. It began lobbying for an upgrade of a 12 km section between Frenchpark and Boyle which would link up to the N4.
In the meantime, it was told that funding had been allocated for widening and paving and resurfacing of the N5.
"We seen no reason why the upgrading cannot be completed over a two-year period," Mr Brennan says. "Roscommon County Council has confirmed that the required improvements could be expedited, if funding was available. It stands to reason that we must invest in infrastructure if we are to sustain a path towards growth."
The NRA says it is providing funding of approximately €5 million annually over "the coming years" to improve pavement quality in Roscommon and Co Mayo, but it is not in a position to increase the allocation for pavement improvement and widening, or to accelerate the completion of planned works due to extensive demands on the authority's financial resources. It says it will keep the position "under review".
It states that planning and design work is due to begin this year on the Strokestown by-pass, and proposals are being pursued to extend the scope of the Ballaghadereen by-pass.
A strategic study has been initiated to examine the feasibility of developing an N5/N4 link, it says.