The Bombardier Mark 1 vehicles are the oldest on the Skytrain network, dating back to the opening of the first phase of the system in 1985.

Canada's federal government is contributing $C28.5m towards the project, which is due to be completed in December 2016.

Work includes upgrading the electrical system, expanding the interior passenger capacity, refurbishing passenger doors, replacing interior amenities, and an exterior repaint.

Translink says replacing the fleet with new-build vehicles would cost around $C 262m.