pauls wrote:I was thinking of sleepers and ballast - I just wasn't clear about it - so in other words the lofted object would be rails only.
Ah, I ignored that you were talking about fixed pieces of track. For them, including the ballast in the population item or otherwise fixed shape, of course, is an option. Only for curves, you would change Z fighting for Z fighting if you would attach a stripe of ballast to each sleeper, as they would overlap in curves. But then again not, if you create the shape in such a way that the excess ballast bit digs into/under the sleeper shape, where it is invisible.
Following your logic, wouldn't is be a solution to have a lofted item which is just a horizontal plane with sleeper & ballast texture, floating 2 cm over the normal trackbed shape? It would not bury the rails too badly, and maybe 2 cm are enough to make it a clear winner in the Z fight. I never tested this, but Derek mentioned 1 or 2 cm as a distance of the shining pane of illuminated building windows, which also must stand off the house to prevent Z fighting.
Maybe placing such a shape over only one of the two arms of a switch would be enough, and doing it with the offset tool (offset 0.01 or 0.0001 or so) would allow for a one-fits-all solution.
If the basic idea works, then what about constructing a track where the ballast and the sleepers are skewed to one side, by 2 cm. Maybe it would not be too noticeable, and then the Z fighting would only occur in the very first part of the switch. But I am afraid to really benefit from the idea, the skew would have to be more, and it would then look funny.
With 3D sleepers, you could further develop this idea: The ballast often is a bit on the high side near the track and much lower in the middle. This means that if the sleepers are a shape of their own, the ballast surface could be a pronounced V or M shape, up to 10 cm lower in the centre, which would be a 70:10 grade. This should really reduce the Z fighting in switches. But it does not solve the problem of 3D sleepers in switches.