Work begins on Ffestiniog Railway bridge
Work is starting on a rail bridge to carry historic steam trains over the new £35m Porthmadog bypass.
The steel structure will take the Ffestiniog Railway line over the new road at Minffordd, on the Penrhyndeudraeth side of the town.
In preparation for the work railway staff have removed signals and a stretch of track at the site dating back to 1835.
The railway line should reopen to passengers in March.
The work is being carried out by Balfour Beatty and Jones Bros Civil Engineering as part of the bypass construction for the assembly government.
Bypass workers will dig down 20 ft (6m) to the level of the new road at the site.
Alun Jones, public liaison officer for the project, said the bridge was a major milestone.
"We are working to ensure there is minimal disruption to this much-loved rail route," he said.
The new section of the A487 will improve journey times, and ease congestion at Tremadog, Porthmadog and Minffordd.
Part of the new road past Tremadog is expected to be ready in the middle of this year, and the entire bypass finished by the beginning of 2012.
Clare Britton, commercial manager at Ffestiniog and Welsh Highland Railways, added: "The bridge represents a fairly significant alteration to the line at Minffordd.
"We have a good relationship with the bypass team and are happy to give the project our full support for the benefits it will bring the area as a whole."