What are those filler caps on modern locomotives

You are correct. Traction sand.

Gilly

I started to say windshield washer fluid...

Nice, thank you! ... but where does the washer fluid go!? (kidding)

LOL no washer fluid.

Rick

Actually, I think some Canadian locos do have washer fluid. The ones that I operated had the feature, but, there was never any in fluid in them.

When you go through the front door, there's a little room in the nose of the cab on the left where the blue fluid goes....

Gilly

All joking aside, I never looked for the container. Like I said, these were CP units. On further thought, it is probably as much for deicing windshields than for cleaning purposes.

One time I had a CP unit back in the consist that someone had left the window heater on. The window was so hot I could barely hold my hand on it! The NS units window heaters never got that hot.

On BNSF, we had windsheld washers on all modern GE's. Problem was, it only sprayed from the center of the blade arm, and really only washed the bottom of the wiper path.

Everywhere but the windshield!