This isn't just JR's ballast, but all textures that run at an angle with a tight radius. I agree with Dave. The only way to fix this is with grass splines and blending textures. What I do is place a dark texture down much wider than the track. This is usually a darker ballast similar to old coal cinders which are still found along ROWs today. With that wider base in place, I then place a much narrower track-colored ballast, though not as narrow as you have. Combine this along with vegetation and darker plants, grass, etc., and this effect nearly disappears.
John
