We recently commissioned a low dog indexer/progressor.  You can see it here keeping cars moving at a continuous speed.  It can also be driven on by trucks with grain trailers.

Calbrandt's Axle Railcar Mover Progressor consists of two independent carriages, each consisting of two hydraulic cylinders in series pushing on an axle carriage.  The progressor provides continuous movement of the railcars.  when one carriage fully extends it hands off to the other carriage to move the railcars forward.  Typical overall stroke is 70 feet.