Both lanes of the Dublin Port tunnel re-opened this evening after being closed this morning for safety reasons.
The closure caused delays to rush hour traffic and gardai were in place to assist traffic flows for the evening rush hour.
A Garda spokesman said this evening that traffic had returned to normal after the closure at 10.15am following the discovery of problems with the safety system which monitors height detection of vehicles, fire suppression mechanisms, closed circuit television and emergency lighting.
Sean O'Neill of the National Roads Authority (NRA) said earlier that the safety system was the tunnel's "eyes, ears, nose and throat".
The closure meant added traffic in the city centre wiht heavy goods vehicles on main transit routes, particularly the quays. The ban on their entering the city centre has been lifted to aid the flow of traffic.