Bridge clearance

[selector]

You need an absolute, rock bottom, don't-even-ask, 2.6" for 95% of what you are likely to run. That will let a Lionel Challenger pass below with no paint scraping up on the cab roof.  Obviously that is too low, so I figure closer to 3" for looks, now that the safety part is determined.

But it is not quite so easy.  Whatever the upper tracks must use for support/roadbed is going to have a thickness, or a height if you will.  So, the 3" clearance above the lower rails must be to the bottom leading edge of that supporting complex, whether a girder bridge or the top of a large steel culvert.  That means you must factor all this in to our grade calculation, and you may find that you need something closer to 3.5% for your grade after all.  If that is a no-go, then you have options to alter your upper support compex, or even to have the lower tracks dip on a slight grade to that point, thus buying you some extra clearance at the bottom of the dip, after which it rises again to its previous level.  Some fellas have to do that to keep their grades from getting out of hand.

[bogp40]

I always use 3" as a bare min for clearance itself (3 1/4-1/2") allows breathing room. When working with railhead to railhead 4" is a general rule. Most bridges will only be no more than the 1" unless there are extremly thick/ tall girders. You need to adjust for for the bridge type.

If you find that you're grades create close clearance, using a short ballasted deck bridge built with 1/4 or 3/8 plywood. The track can be bonded to the ply and the the girders glued to the plywood sides.  Remember if clearances are too close for comfort or you would like more clearance for a better or longer bridge, the lower track can always be dropped before the overpass.

On the club layout, I have the opposite problem. Many of all the track crossings are 5 1/2 - 6". This poses a problem with scenicing all my abutments as most ready made castings and molds are all 4" tall. Custom molds are made or other creative measures are needed in this case.

[TomDiehl]

First, remember to measure the clearance height from the railhead of the lower track to the underside of the trackbed of the upper track. The minimum height will vary depending on what type or era of equipment you're planning on running on this layout. For example, Superliners require more clearance than Amfleet coaches, which is why Superliners aren't used on the Northeast Corridor. You'll need to measure your highest loco or car, then add a bit of height for safety.

[Anonymous]

Hello everyone, I am new to this forum, but I have just completed the benchwork for my 6X13 HO layout. Anyway, I have read about what is the minimum clearance height I need to have for a bridge where trains will also run under it. I want to make the height the minimum I can get away with, in order to keep my track grade to 2 1/2 or 3 percent leading up to the bridge overpass on both sides. Thanks for any suggestions.