The Sarmiento line, running between the stations of Once and Moreno, is one of the busiest suburban lines in Buenos Aires, with rush-hour frequencies of around 7-8 minutes. It had suffered incidents due to degradation of the rail superstructure and essentially of the signalling and telecommunications systems, combined with a large number of very busy level crossings in an urban area. In recent years the Argentinean government decided to undertake renovation of the rail superstructure (ballast, track and sleepers) as well as replacement of the sidings and improvement of the surface on level crossings. An audit was made of the track renovation carried out, detecting remaining problematical points and proposing improvements in the processes of construction site supervision.