GARDAI are developing plans to fine and prosecute motorists using the Dublin Port Tunnel amid mounting concern over speeding.
Cameras mounted at the entry and exit points may be used to determine the average speed of motorists in the tunnel.
New figures seen by the Irish Independent reveal over half of motorists using the tunnel are speeding - but none are being prosecuted or hit with penalty points.
The problem is most acute in the tunnel's south bore, where seven in 10 motorists were found to speeding. Gardaí have not been operating a normal speed enforcement regime in the tunnel, which opened in 2006 and is used by 15,000 vehicles a day, because it is not safe for officers to use speed guns.
There is also nowhere to safely pull in vehicles on the approach to the tunnel or inside it.
It was possible to tell the average speed of the vehicles using cameras at entry and exit points. However, the cameras currently in place are not suitable for use in prosecutions.
There has also been uncertainty in the past over whether the average speed evidence could be used in court.
Legislating for average speed evidence formed part of the Government's Road Safety Strategy 2013-2020.
However, the Irish Independent has learned this stumbling block has now been overcome after the Department of Transport received legal advice that no new laws would be needed to allow average speed evidence to be used in prosecutions.
The NRA said it was now in talks with garda management to "develop a mechanism" for this "as soon as possible".
No date has been set for enforcement to begin, but it is hoped to be by the end of 2016.
Figures released under the Freedom of Information Act by the National Roads Authority (NRA), to Fine Gael TD Fergus O'Dowd, reveal speeding is rampant in both bores of the tunnel.
Almost 45pc of motorists using the north bore last November were clocked driving above the 80kph speed limit.
The statistics are even worse in the south-bound bore where 70pc of vehicles exceeded the limit the same month.
The average speed of vehicles using the south bore that month was 85kph.
A small number of motorists were clocked doing speeds in excess of 120kph in both bores.
It is understood that the new speeding detection in the tunnel is likely to be outsourced rather than being carried out by garda traffic officers. New technology will also be required.
Mr O'Dowd said the speeding statistics were "extremely concerning".
"People are flouting the law and there are no penalties being applied. My concern is that if there is an accident there, it could have extreme consequences," he said.
"Accidents in tunnels can lead to significant fatalities."
The speeding data showed that 36.1pc of motorists using the north bore drove at between 80 and 91kph on average last November. Another 6.74pc drove at 91 to 100kph on average, 2pc between 100 and 120kph on average, and 0.1pc above 120kph.
In the south bore, 47.2pc of motorists were found to be driving between 80 and 91kph, 17pc between 91 and 100kph, 6.4pc between 100 and 120kph, and 0.26pc above 120kph.
In a letter to Mr O'Dowd, the NRA said: "Normal speed enforcement methods are not suitable in a tunnel environment due to health and safety risks to the operatives.
"Best practice for determining speeds of vehicles in tunnel environments involve the use of cameras located at each portal which enable the average speed of vehicles passing through the tunnel to be monitored."