A two-week train line closure allowed for major upgrades between Brockenhurst and Lymington Pier.
Following the installation of new track on the line in late October, the bridge across the Lymington River between Lymington Town and Pier stations has been strengthened.
Engineers also refurbished and repaired heavily corroded critical steel elements of Lymington Viaduct, carried out from pontoons and underslung scaffold.
The wheel timbers, which support the track across the viaduct, have also been replaced.
The track across Lymington Town Level Crossing was replaced, and improvement works at Brockenhurst Level Crossing were completed.
Mark Goodall, Network Rail’s Wessex route director, said: "I’d firstly like to thank any passengers and local residents who may have been disturbed by our engineering work over the festive period for their patience and understanding.
"The work our teams have completed over the past couple of weeks is critical for the continued safe and reliable running of the railway and I’d like to pay tribute to the many men and women who have worked so tirelessly and forgone spending festive time with family and friends to complete this work.
"We’re committed to running a high performing, reliable and punctual railway and I’m delighted to welcome passengers back to an improved railway in 2025."
A South Western Railway spokesperson said: "The Christmas and New Year period saw a huge amount of engineering work carried out across our network, such as on the busy South West Main Line through Brookwood and on the Lymington branch line that is so important to its local communities.
"We’re very grateful to our customers for their patience, particularly those whose journeys were longer or involved rail replacement bus services. The maintenance and improvements that our colleagues at Network Rail have completed will ensure that our services can run safely and reliably for many years to come."
The junctions at Brockenhurst station also underwent tamping, a process of compacting the stones that support the track.
The improvements aimed to ensure the reliability and safety of the branch line, which is a crucial link for rail passengers in the area.
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