Completion of major engineering work on the Sleaford avoiding rail line was marked with a commemorative plaque at Boston Road bridge.
The new bridge is in the parish of Kirkby la Thorpe and parish council chairman Rob Hipworth formally unveiled the plaque on Thursday.
The work on the avoiding line is part of a £280 million project to modernise and upgrade the 86-mile Peterborough to Doncaster line that passes through Spalding, Sleaford, Lincoln and Gainsborough.
The scheme, known as the GNGE project (Great Northern Great Eastern), was started last year and is expected to be completed by next autumn.
The Sleaford avoiding line was used to enable trains to bypass the town but it fell into disuse in the 1980s. The modernisation of this section, so that trains not stopping in Sleaford can again avoid the town, is the centrepiece of the project.
The work has included the replacement of bridges along the avoiding line.
GNGE project director Ian Quick, of Network Rail, said: “The restoration of the Sleaford avoiding line is a key element of the GNGE project. We would like to thank the people of Kirkby la Thorpe, Sleaford and other nearby communities for their cooperation and understanding while we undertook these vital works.”