BIG working photo ...
Depending what kind of tool is in the end of the excavator dipper, it could be picking up old ties, distributing new ones; or with a magnet, misc steel items (spikes, tie plates etc), or even doing ditch cleaning with a bucket. A versatile machine.
The 'rails' on the bottom of the excavator allow it to move from car to car and fill up each car, or empty them.