The "rail dust" seems to apply to anything that is rusty metal in the paint -not necessarily from rail cars. Heck, my car was made less than 100km from my house and it never saw a rail car. When I got the car (used) it had the rust specks everywhere. The majority was behind the front wheels and rear wheels which makes me think it's also metal from the brakes on the car itself. I used a clay bar to start but it is a lot of work and then tried some "Nevr-dull" which is a polish in a wadding material. It's used mainly for cleaning chrome. Worked great and was a lot easier. I washed the car again after to remove the polish haze. I plan to polish the entire car with a DA next week too. I did not see any damage done to the paint with the Nevr-Dull . There were no scratches either, however, since I was using it outside the intended purpose then it's a "try at your own risk" suggestion.