The NMRA gauge isn't friendly

The NMRA gauge isn't friendly enough. Better check it with an autorack or, even better, an AirBox aircraft enclosed flat. They're both taller than that doublestack.

EtA:

Just checked with my AirBox... the top of the car is 1.525" from the top of the rail. Better plan on at least 1.6", better 1.75" for clearance unless you have a scale reason not to.... there's a reason 2" is the suggested clearance under bridges and such.

Clearances

There was an article on clearances back in July of last year

Maybe if you get a run for it

Maybe if you get a run for it you can get it in there.

Rob in Texas

Designed before doublestacks

The NMRA standards that the guage represents were designed before double stacks and high-cube containers.

The real railroads had the same problem.  They developed several solutions to solve it, which they mixed and matched as needed:

1     use smaller diameter wheels on the cars to get them a bit lower

2     dig the roadbed down 

3     carve square chunks out of the top of the portals and, where necessary, material from the top of the tunnel

4     restrict doublestack cars to only one container high on affected routes 

Number 1 actually started with the Tri-level autoracks, most of which also having lower ride heights (all N scale tri-levels are much too high; as yet none actually attempt to be anywhere close to true to prototype), and number 4 is most common on Eastern roads which have even lower tunnel clearances that reflect the much smaller size of equipment at the time they were built. The N scale AirBox models either suffer the same problem as the N tri-levels or the prototype cars would fit into the "high, long and wide load" category, which would make it necessary for the traffic department to carefully plan the route they take.

On the LP, I found a variation of number 4 worked.  Doublestacks just squeak through if I use only one high cube  container in a stack, with the other being a standard height.  I only had to adjust the clearance of a couple portals that way.

For us N scalers, N-trak sells a guage designed to check clearances for double stacks.

Oversize Cars

The problem is more likely occurring because of rolling stock or containers being oversize. NMRA standards list overhead clearance to be 3.00" for HO and 1-21/32 for N scale. Both of these equate to just about 22 feet actual size. Researching the web for standard railroad overhead clearance minimum, it is listed to be the same 22 feet.

Clearances

When I built my RR (mid 50's Espee), I used a double stack well car and an 86' hycube to check for and establish clearances in the numerous tunnels and helix. That way I knew that I could run anything in the future without fear of any impaired clearance issues.

So far, I've never had a problem.

PS-not rue. One bridge I built after this time frame had guardrails too close for clearance near the end where the track came out of a curve. Had to redo those. The hycube & company had departed before that time.

Still having braincramps

Espee over Donner

After you get height clearance checked

with that double stack, I'd highly suggest running an 89 foot flat car for around the curve clearance.  I have one just for that purpose to check trees, buidings, etc.

Oops

When I worked for the Chicago Central someone did not check to consist close enough at Council Bluffs IA, there was a couple of autoracks on the train and nobody noticed it until after the train went through the tunnel at East Dubuque, IL. The top row of cars were smashed!

Pete 

Meanwhile on Conrail...

< < rolling along towards your overpass

Hmmm... let's see now...   21/32.... that's 0.5328... add the inch... it's 1.5328... so we'll clear by... Hmmm....   subtract the 1.525.... -0.00119

So it'll clear by...

CRUNCH

Oops... that was a minus sign there, wasn't it?

The Airbox STILL won't clear!

Another solution...

I was modeling "modern era" at one point on my old C&S (BN) layout.  One of the operators brought over a double stack car and an autorack to "update the fleet".   Well, neither of them fit my deliberately undersized clearances. 

Solution: roll back the clock to 1968 and repaint the engines in the more attractive and colorful 1960s colors (black and gray, red and gray). I also traded all my BN rolling stock to another modeler who was going the opposite direction.  

Defect - detector - milepost -.....

Dear MRHers,

Happy Modelling,
Aim to stay inside the clearance diagram,
Prof Klyzlr

"Clearance" is not a maximum hole size

It's important to note that the "clearance diagram" is a MINIMUM, not a maximum. There is absolutely NOTHING prototypically incorrect about having MORE clearance than required. Why would you choose to handicap yourself, your layout, and your operations unnecessarily?  You're not paying to carve your tunnels out of solid granite or haul away another 500 tons of rock, and you can easily shim that portal  a little higher. Another quarter inch of clearance can make it a LOT simpler to reach under the bridge if you have a derailment on the other side of it.

Don't design your layout for minimum clearances... especially PROTOTYPE minimum clearances that would have you scraping someone off a ladder on bridge abutments, for example... unless you have an EXTREMELY important reason for doing so. Everything else on your layout is a compromise between scale fidelity and practical reality - there's really no good reason for clearances to be one exception. Your mainline isn't thousands of miles long, you don't have to climb 3000 scale feet to get through that mountain pass, odds are your trains aren't even close to prototypical lengths, your curves aren't half a scale mile in radius, and your trees probably top out at about 30-40 scale feet tall. Don't obsess about accuracy for something that WILL cause you trouble if you don't make allowances for it.

NMRA Gage

Part of this discussion seems to be whether the NMRA Gage works for clearances. I use it as my standard (though I model in HO) and never had any issues with cars hitting overpasses or tunnel portals.

Does the N Scale Gage measure at the 1-21/32"?

How tall is the Airbox car supposed to be in actual size?

Some of this math isn't adding up....my calcs show,   1-21/32 = 1.656 - 1.525 (Airbox Size) = 0.131 Clearance

Time is important

Here's a link to a good discussion on the NMRA site.

http://www.nmra.org/standards/sandrp/gauge.html

and clearances:

http://www.nmra.org/standards/sandrp/pdf/s-7_2011_02.pdf

There is no single set of clearances. They vary according to time and place. The July 2013 MRH article gives suggestions on creating a clearance diagram for your personal railroad. Also check the NMRA  references; there have been some changes to the NMRA clearances since the article was written.

Do it this way

Make a tunnel out of it with abandoned track ..and make a new right of way next to it if you can with proper clearance...Grand Trunk Western ran almost 100 years thru small tunnel untill they finally made a new one for double stack containers in the 1990s...so  make it look like that  you didnt oops  you made an engineering change for the better posperity of the railroad.

Kevin

If that's a reply to the

If that's a reply to the original post: That's not a tunnel portal, it's a backdrop hole which is supposed to wind up hidden by scenery. The backdrop is styrene, so nibbling a few millimeters off the top won't be a problem .

And in reply to someone else: my Atlas autoracks are actually a little shorter than the double-stack (though I should check all my other well cars while I'm at it).

Mission accomplished

With a little careful carving, the portal is now high enough.....

....which allowed me to find out that another mousehole (on a minimum-radius curve) further north had side-clearance issues on the well cars and other long rolling stock. Now widened and tested with a 85' passenger car....

Rob in Texas is right

Hehehe...I tell that to my guys at work unloading tractor-trailers all the time, trying to get a tall pallet out but under our 'over-the-dock-door' pallet racking- "if you go real fast it'll stretch out and make it.  Einstein said that the closer you are to the speed of light the more things stretch, so go for it!"  

So far Einstein has been proven wrong every time.

The experienced guys laugh, the new guys pause and look at me like "that really works?  Really?"  Always good for a laugh!

Reasons for close clearances

Dear MRHers,

It should be noted that particularly on show layouts, where "mousehole" exits to/from staging yards are almost as "predictable as death and taxes", keeping things at close-clearance is a visual necessity...

Note the clearance of the railcar's roof-mounted radiators, and the comparative clearance to the 7505 and guards-vans clearance thru the same exit...
(Hint: the hole was initially cut to clear 7505, break out the Dremel...)

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Worlds Toughest Tunnel?

At least you did not end up on a video like this!

Thomas Gasior