The new Borders Railway will open in summer 2015, with more than 400 jobs being created to build it.
The new line will have seven new stations – at Shawfair, Eskbank, Newtongrange, Gorebridge, Stow, Galashiels and the end of the line at Tweedbank.
The 35-mile route will run from Waverley to the Borders.
Site clearances, ground investigations and mine remediation works are under way.
A tunnel will be built beneath Edinburgh City Bypass this summer, with 50,000 commuters diverted each day along a temporary two-lane carriageway to allow for a 130ft-wide section of the road to be removed.