I have some scale wheel cars that very ably negotiate Atlas O 072 switches without any problem. I have others that seem to derail at the frog. My "analysis" is that the guardrail...opposite the frog is not doing enough to keep the scale wheels from "clipping" the tip of the frog and, then, derailing. My solution would be to make that guard rail a little "thicker" or "wider" toward the rail to cause it to better guide the wheel through the frog.
Have any of you modified that guard rail? If so, what did you do? My inclination is to glue a thin piece of plastic to the wheel side of the guard rail...thereby keeping the scale wheels pulled left and away from the tip of the frog.
What materials and techniques did you use??