Work on fire-proofing the Jack Lynch Tunnel will take just half the time originally anticipated and will get under way on Sep 1.
The €5m project, which is required under an EU Directive, will necessitate night-time closures.
When first mooted, engineers thought the project would take six months to complete, but now believe they can do it in half the time.
A tunnel management team spokesman said by closing overnight, the number of tunnel users affected will be minimised.
On average 91% of the total traffic passing through the tunnel does so between 7am and 9.15pm.
“The upgrade works will see nightly closures from 9.15pm to 7am every night with the exception of Fridays.
“A contra flow system, which has been adopted for previous tunnel works, is not feasible in this case as for long-term closures they pose safety issues. There will, however, be a blue lane to facilitate emergency services vehicles, should they need to pass through,” the spokesman said.
The work is scheduled to be completed by BAM Contractors on Nov 30.
Details of alternative routes will be provided at www.jacklynchtunnel.ie and live updates will be available via email, SMS and Twitter.
Road users can sign up to an email or SMS notification service on the same website, free of charge. People can also do this by texting TUNNEL to 51444.
A dedicated free phone hotline will also be set up for the duration of the works which will give up- to date, live closure information 24/7.
Further details on this will be made available in the coming weeks.
© Irish Examiner Ltd. All rights reserved