Works on the Blackwater Bridge outside Monaghan town are expected to be completed in the next six to eight weeks.
The next phase of work on the N2 bridge begins this morning with changes to the traffic management system.
This week traffic travelling northbound in the N2 will travel via the new bridge, with southbound traffic continuing to use the temporary one.
From next weekend a stop-go system will be in place.
Closures of local roads in the area will also take place in the coming weeks to allow for resurfacing works.