ABSTRACT
Until the early 1970s, railway tracks all over the world were laid on ballast, which is replaced every 15.;.-30 years, whereas the maintenance of track takes place every 3.;.-5 years. Maintenance and renewal of ballast are conducted under extremely difficult conditions in the intervals between successive trains, usually during the night, and the available time for maintenance or renewal works is usually smaller than 3.;.-5h.
