Trains are due to begin operating on the new route in December
The first length of new tracks on the £330m Airdrie to Bathgate rail link have been laid.
The project, which will create a new route between Glasgow and Edinburgh, is due to be completed later this year.
Operator First ScotRail is currently in dispute with the RMT rail union over staffing on the new link.
Rail workers have taken part in two 24-hour walkouts over proposals which would see drivers, rather than guards, open the train doors.
The union has said the move would jeopardise the safety of passengers but that claim is disputed by First ScotRail.
The company insists the trains are safe, and are the same as those which have operated in Scotland for 25 years.
Network rail chiefs and local MSPs from areas the new rail route will pass through attended a track laying ceremony in Bathgate.
The route is due to be operational by December.
It is designed to complete the "missing link" for communities between Glasgow and Edinburgh.
There will be new stations at Armadale and Caldercruix; re-located stations at Bathgate and Drumgelloch and upgraded stations at Airdrie, Livingston North and Uphall.
A third 24-hour strike by rail workers is planned for Saturday, the day of the Scotland v England RBS 6 Nations rugby game at Murrayfield.