"Aire! Oibrithe bothar" warn the signs. But the "road" is riding out to sea, the first phase of Galway's £45 million sewage plant on Mutton Island in Galway Bay.
The temporary causeway has reached the halfway mark, is clearly visible to strollers on Salthill's promenade and extending at a rate of 45 metres a day. Two excavators mark the skyline, shifting and shovelling rock and spoil.
Even at night their lights have been visible; last week the operators took advantage of a full moon and low tide.
Truck-drivers from as far as Inver, Co Donegal, have been delivering 3,000 tonnes of limestone daily. The 18 to 20 "hackers", as they are known, waste no time on the circuit between South Park and Two Mile Ditch quarry. It is valuable work at this time of year, according to Mr John Morgan, project resident engineer with P.H. McCarthy, one of the main contractors for Galway Corporation.
The construction of the temporary "pier" was one of several options open to partners Ascon, a company with considerable marine engineering experience. The main task was laying an 890 m pipe from South Park to the inlet station for the pumping station on the island. It could have been floated out, but it was felt that use of a temporary bank - from which to dig a trench on the causeway's eastern flank and suspend the pipe lengths - made better sense.
The pipe is due in from France next week. Then a surreal structure in South Park will come into its own. The 15 m pipe-lengths, with a diameter of 1.8 m, or just over six ft, will be deposited on temporary plinths of concrete and timber set out in the park. They will be welded into 75 metre lengths for eventual transfer to the trench.
"The plinths will then be removed," Mr Morgan says. "This whole area is going to be landscaped again when we have finished. And South Park will have its shore walk back."
The trench is being carved out just under the seabed's surface. Once in place, the causeway will be folded over on top of it. The £6.2 million job is on schedule, and the target date is Easter.
By September, the project moves into its next phase - construction of the sewage treatment plant, which received final planning approval in a Supreme Court appeal last May, after a long and bitter battle over its location.
One group looking forward to its construction is the Renmore Residents' Association, which says it will result in the reinstatement of Ballyloughane Beach, to the east of the city, as a clean and safe place for swimming again.
The association is objecting to a rezoning proposal in the draft city development plan, to allow housing to be built on a green belt near the beach.
No details of the sewage plant design are yet available, and An Taisce's Galway branch has also raised concerns about the corporation's plans for disposal of the waste sludge from the plant. Mr Joe Gavin, Galway City Manager, says no decision will be taken until a national strategy group on sludge disposal has made its recommendations. Internationally, the jury is still out on the most effective and safe method of disposing of sewage sludge - the biosolids from sewers. The EU has ruled that dumping at sea will be illegal by the end of this year. Landfill sites are becoming congested, and rotting sludge emits methane, a potent greenhouse gas. Incinerating sludge can release air pollutants, and is three to six times more expensive than spreading on land.
In Europe and North America, between one and two-thirds of sludge is now spread on farmland, according to a recent report in New Scientist magazine. In the US, France and Germany, all sludge is treated before being used as a fertiliser, to make it more chemically stable. Only Britain permits farmers to put raw sewage on their land, though pressure from food retailers is likely to put a stop to this by the year 2002.
The Washington-based World watch Institute says sewage should be regarded as a valuable resource, rather than as pure - or impure - waste. Only by separating faeces from industrial and household wastes can its full potential be realised, however - and that means abandoning the use of mixed sewage systems by most industrialised countries, including this one.
All a bit academic, perhaps, as far as Mutton Island is concerned; the Admiralty Chart for the bay has already been amended to denote "causeway under construction".