Railway bridge over track

[cheese3]

I would play it safe and use 4 in. If you use 2 in foam all you need is 2 pieces stacked and you are there.

[Anonymous]

NMRA Standard S-7 gives a minimum of 3 1/6" overhead clearence above the rail head for standard HO scale.
If you are running double stack trains, Hi-Cube box cars and auto racks, 3 1/2" may be needed. I use a mimium of 4" of overhead clearence for hidden track. Check the tallest rolling you want to run and use that for checking clearence.

[bogp40]

3" is the absoute min. for actual clearance. Railhead to railhead is a different story. You will need to figure what type bridge and how much added clearance needed for supporting girders, bridge ties and other framework. To be safe, I will use 3 1/2" as a rule to give a little bit of insurance. The NMRA track gauge placed upright on the rails shows you the bare min. for clearance.
Bob K.

[electrolove]

I wonder what the recomended minimum distance is if I want to have a railway bridge over my track in HO scale?

Thanks in advance