There are a few ways this style can be created To do it in a single style use two compose operators to create sets of horizontal and vertical planks. The vertical planks are relatively straightforward but the horizontal ones take a little more work, to position them use Fixed Y-Translation to move one above the other and then left and right padding to make them overlap. A tip here is that if the sum of a segment's left and right padding is >= its width, then the segment will disappear, so to resolve this split the segment's width measurement between the current and preceding segment's padding. To illustrate, if a 300mm long segment has a left padding value of -150mm, the preceding segment would need a right padding of -150mm too. Below is a screengrab of the node tree for this technique.
Alternatively a much simpler approach is to nest one RailClone object inside another. To use this technique create a simple RailClone object with the number of segments you need for each panel, in my example I used 3. Add the material ID randomiser to this style too.
Then create your floor style and select this RailClone object as a segment. Make sure you turn on "Nest" from the segment's properties to allow the Material IDs to be re-seeded every time the segment is used. The finished style should look like this:
I've attached a file so you can have a look at both these techniques in more detail.
Hope that helps,