THE Dublin to Belfast rail service is facing "death by a thousand cuts" and needs a €520m investment, it has been claimed.
Plummeting passenger numbers have caused fears for the viability of the service.
A new report, by the Department for Regional Development in Northern Ireland, shows that 740,000 journeys are now made on the city-link a year – down 213,000 from 10 years ago.
And it warns the line will need an investment of €520m over the next 12 years.
The proposals include at least six high-speed electric trains and a track upgrade from Belfast to the border to permit speeds of 125mph.
Stewart Dickson, of the Regional Development Committee, said: "The cross-border rail service is really falling behind in terms of competition from the new road.
"There is a strong argument for saying we should get European investment, but unless we can get that, it is not viable and we will just see the death of the Belfast to Dublin railway by a thousand cuts."
The report says that the 22pc decline in North-South train commuters is the result of a series of factors, including improved road services and the economic crash.
Another reason is the collapse of the Malahide bridge in 2009, when a replacement bus service was in place between Drogheda and Dublin.
Politicians in the North say it is "extremely worrying".
But the CEO of the Dublin City Business Association believes that the decline in passengers using the Dublin-Belfast rail line will have little effect on businesses in the capital.
"I see it as a positive rather than a negative," David Brennan said. "My concerns are for how it may affect retailers in Dublin but I see it making only a very small difference to them."
Irish Rail was unavailable for comment at the time of going to press.