Transport secretary says Scottish Government will try its 'very best' to keep any cost increases to a minimum.
Report by Network Rail chief on 25 mile long connection - dubbed 'Boris's burrow' - due to be published within weeks.
Cross-border operator to serve town with 96 more services a week and make it a 'key transport hub'.
The Scottish Greens want the government to 'seize the opportunity' to improve air quality and reduce congestion.
Industry leaders say loss of coach firms could jeopardise tourism in the region.
21 road accidents resulting in injury were recorded between Tyndrum and Lix Toll.
Construction of the £207m line to Newhaven is scheduled to last until summer 2021.
Councillors approve plan to completely transform Glasgow's civic centre.
Industry leaders believe buses can be part of the solution with a shift from private cars to sustainable transport.
The limit will be introduced to residential streets, the city centre and where there are high levels of walking or cycling.