The 25.1km line opened in October 2012, but a section of the route has been closed since March, when six metro cars were taken out of service after the vehicles were found to be causing serious damage to track.

TSO, France, has been analysing the problem since April, and Systra will use the data gathered by TSO to assess the necessary remedial works.

Responsibility for the problem has been denied by both rolling stock supplier CAF and the construction consortium, which includes ICA, Carso Infraestructura y Construcción, and Alstom. While arguments continue as to who is to blame, the government has said it will initially cover the cost of any remedial work pending a final decision over which party is liable.

Preliminary findings have prompted five recommendations, including a review of the application of lubrication to trains and fixed systems, the replacement of needle switches, and gauge adjustments on curved track.