I learned the hard way - how much fun could I take????
If the bar codes were on the baseboard between the sleepers/ties, the process would take care of itself! Hydraulics and/or pneumatics _could_ be made to work, but given that internal working clearances and friction can't be scaled, I'd rather go with mechanical linkages and electrics/electronics and servos.
The point I was trying to make is that the flow can only be reduced to three marbles width before it becomes unreliable. Sure, you can block it, (>1 marble) or control the rate lof flow (
I don't see an advantage - other than clearing for wheel flanges. A blade and brush can do that behind the hopper.
Those cell phone vibrator motors run at about 1.5 volts - simple to arrange with a diode bridge rectifier, resistor/bulb etc.
Why not just a plasticard plough and a fixed brush? I'm assuming slow speed operation here, rather than an ICE/TGV/Bullet train.
I rigged one of those cheapie computer vacuum cleaners into a wagon. Right angled bend in place of the longish 30 degree neck, and a 90 degree bend for the bag, which is normally straight out at right angles. The result was a little better than not vacuuming :-) MkII was/is to be the sucking stage mounted at one end of a long passenger coach with the exhaust directed along the coach. A part high wall causes the airflow spped to drop in the middle third of the coach, then a mesh wall and the last third of the coach has the window glazing removed to allow the air out at low velocity. Still need to find a suitable coach with a clip-on roof, and time ...
Greg.P.