Network Rail has completed track laying between Airdrie and Bathgate in Scotland.
The 24km line will carry four trains an hour between West Lothian and North Lanarkshire, and open up transport options between Edinburgh and Glasgow.
The route will also include new stations at Calderdruix, Blackridge and Armadale as well as two relocated stations in Drumgelloch and Bathgate.
The £300m ($462.6m) rail link was funded by Transport Scotland and is expected to be open by December 2010.
The completed route will be the longest domestic passenger railway to be built in Britain for a century.