12 pillar set for Märklin H0 C track up to 78mm (about 3 inches).
78mm should be enough for a second crossing below. Please check it before, especially for trains with current collectors.
UPDATE V2: now customizable. Now each pillar is numbered and labeled so it is easy to distinguish them.
Please note the pillars are angled on the track bed for a better stand. Put one pillar in between each track segment. Be sure you assemble them correct and it has a stable stand.