Ballast train

Seen on the East Lancashire Railway.

Some of the fundamentals or railroad design haven't changed much over the years.  Rails transfer their load to cross ties/sleepers which simultaneously serve to spread out the load over a larger area and keep the rails at the proper gauge.  All of this needs a stable platform and resting it on dirt would be unacceptable for anything that isn't exceedingly temporary.  Crushed stone ballast is used to create the roadbed and spread around the rails once laid in place.  

Naturally part of maintenance is the replacement or replenishment of ballast along the tracks and railroads have long used special hopper cars to accomplish this.  A train like this (albeit usually a longer one) would have a crew of men with shovels and rakes to spread the ballast while someone manned the gates on the hoppers to dispense the stone as needed.  

Now skip forward to the present day.  A Herzog ballast train has added features Mr. Stephenson couldn't have predicted.  

Those solar panels are a clue that these cars are more than just mechanical devices.  They use a computerized system for dispensing the ballast.  Herzog systems can be tracked and triggered by GPS so that metered amounts are dispensed along the track but not at switch points, trackside detectors, or other inappropriate locations like grade crossings.  They can also be controlled by one or two people on the ground who use a handheld radio system to trigger each ballast door individually.  You can even see the radio frequency ID numbers on the side of the car.  

There is usually a chase vehicle with someone to clean up any misplaced deposits, but considering you can now re-ballast a long stretch of track at nearly 20 MPH I wonder if the navvies of old would even recognize what's become of the railroads.