Good Rule Of Thumb For Over/Under Clearance?

[Hudson]

Bottom of roadbead/ bridge to top of railhead below?

4" suffice?

 What would be a prototypical minimum?

[jeffrey-wimberly]

I use 3 1/2" from top of railhead to bottom of bridge or ceiling of tunnel.

[Hudson]

I'm in the ballpark then.......I'm busy designing at the moment and I was checking my grades and clearances.........

 

Thanks Jeff!

[selector]

I assume we're talking HO since the figures correspond.  I have gone under 3" with no problems.  In the image below, it is exactly 2.8" and it still looks decent enough...maybe not strictly correct, but it passes the eye appeal test for me.

 

[Hudson]

Lovely Niagara selector! What brand?

The clearance looks very good aesthetically speaking. For a tunnel that's about right.

I'll be publishing my initial track plan shortly and I'll call out the area in question.

[doctorwayne]

I measured my tallest piece of equipment, then made all of my mainline clearances greater than that dimension.  However, I did include a couple of areas with low overhead clearance, on industrial sidings, that preclude the use of a loco past a certain point.

The red "R" on the sign denotes a restricted clearance, with particulars outlined in the Rule Book.  Spare flatcars or gondolas are used as idlers to retrieve or spot cars beyond the reach of the loco: 

This one is much the same situation, with the warning sign hidden by the loco: 

These tracks are even off-limits to some freight cars, adding an interesting wrinkle to operations.

Wayne 

[Hudson]

Wayne,

Is that National Grocers building a DPM kit?

I like the restricted clearance idea, it does add an interesting operational wrinkle...

Martin

[doctorwayne]

National Grocers is made-up from DPM modular parts, with a scratchbuilt roof, and built to suit two very oddly-shaped lots:

 

 

The track in this area isn't yet ballasted, as I'll need to remove all of the buildings in the area in order to add a backdrop for the streets that end at the wall. 

Wayne 

[steemtrayn]

If a 2x4 fits under a bridge, so will anything else including auto-max and double stacks.

[tomikawaTT]

I assume we're talking HO since the figures correspond.  I have gone under 3" with no problems.  In the image below, it is exactly 2.8" and it still looks decent enough...maybe not strictly correct, but it passes the eye appeal test for me.

 

Looks perfect - for the Hudson River tunnels on the NYC north of Peekskill, NY.  Of course, the low clearances in those tunnels caused the Niagara to be built as compactly as it was and prevented NYC from running domes on the Century...

NMRA HO gauge clearance is 3" - inadequate for doublestacks.  3.5" (the height of a standard 2x4) scales to over 25 feet, which should clear anything except a track crane with its boom raised.

I won't even mention my standard - since I model in 1:80 scale.

Chuck (modeln=ing Central Japan in September, 1964)

[Hudson]

Nice, I assume the building to the left is DPM as well. I like how you use odd angles to give a false impression of depth. That is one of my main concerns with laying out a scene.

[dehusman]

There are AAR clearance gauges for the equipment and then the railroad has its own clearance requirements for structures.

Plate B = 15'1" (2 1/8")

Plate C = 15'6" (2 1/8")

Plate D, E = 15'9" (2 1/4")

Plate F = 17' (2 1/2")

Typical standard for structures on industrial track = 23' (3 1/4")

Typical standard for structures on main track = 24' (3 1/2")

Dave H.

[selector]

Chuck, I am taking your compliment to the bank this afternoon.  I know it's good for something!   Thank-you.

Hudson, the Niagara is a Broadway Limited Imports model.  It really is an outstanding engine in my view...maybe not up to brass standards, but they scrambled a long way up that slope before calling it a day.

-Crandell

[dstarr]

Bottom of roadbead/ bridge to top of railhead below?

4" suffice?

 What would be a prototypical minimum?

I'd be happy to acheive clearance for the NMRA gauge, namely 3 inches from railhead to bottom of the upper track bridge/ties/tunnel roof.  Three real inches = 21'9" HO.   Any cars that are taller than that, tough, they get restricted, if necessary restricted all the way to the display case.   

[rogerhensley]

If you need more info, here is a page that gives it. 

http://cid.railfan.net/gauge.html

[Anonymous]

I have been reading this thread with great interest.I am going to be installing a Rix Products old style overpass.It is painted and weathered already.After reading the replies I went an measured mine. The overpass supports measure almost 5" from railhead to botttom of overpass.Based on what I read here this is way too high and I should cut it down but the problem is I have a tendency not to cut straight even being as careful as I can and I don't want to mess it up.I spent way to much time on it. Any suggestions would be appreciated. Bob

[selector]

Not necessarily, Bob.  They made those supports/piers high enough for those whose requirement isn't "the minimum" for overhead clearance.  Maybe your overpassing track will need something closer to a trestle height, or a viaduct-like structure, in which case they tend to be rather higher than the minimums.

By all means, if your grades will be better keeping them low, you can cut off the bottom bits of those supports.  Make it fit.  But if your valley or gorge is bowl-like in profile, you'd only want to cut down the outer one or two and leave the bridge piers requiring the longest reach to the valley bottom longer...if you follow.

In other words, the suppliers were trying to make their offering more useful to a wider range of modellers who can cut off what is there, but who can't add what isn't there.

As for the minimum, only some of us will want or need a minimal clearance.  Some want a lot more height because the grades getting to the overpass dictate a greater height, which this structure will meet in many cases.

-Crandell

[doctorwayne]

I have been reading this thread with great interest.I am going to be installing a Rix Products old style overpass.It is painted and weathered already.After reading the replies I went an measured mine. The overpass supports measure almost 5" from railhead to botttom of overpass.Based on what I read here this is way too high and I should cut it down but the problem is I have a tendency not to cut straight even being as careful as I can and I don't want to mess it up.I spent way to much time on it. Any suggestions would be appreciated. Bob

Bob, if it needs to be cut-down, use a divider to mark it before cutting.  Simply decide how much you need to remove, then set the tips to that measurement, and mark the pieces as required.  Make your cuts a little bit shy of the marks, then use a file or sandpaper to finish the job.  I'm not sure whether it's more suitable to cut the tops down, or to take the excess off the bottom, but, if your cuts are a little "off", the bottom would be the best place from which to remove the excess height.  An application of "scenic effects" will hide any discrepancies.

Wayne 

[Anonymous]

Selector,doctorwayne-Points well taken.Grades are of no concern-flat switching layout.I took the overpass piers to work with me and after doing some thinking on what I read here I did some sketches and deceided to make them 25' from railhead to bottom of overpass.I did mess up a couple of cuts but I figured I will have them face the rear of the layout so they won't be seen.What I did as far as cutting goes was to figure where the initial cut had to be and cut the excess from the top part of the piers, sanded everything as smooth as I could and glued them back together.They actually came out pretty good. Thanks again-Bob