Tunnel portals?

[Tone]

Hi,
Our cofee table layout has progressed to a stage where we need to start making scenery.
I figured a wise place to start would be the tunnel portals...
Are there any NMRA or otherwise regulations that should be followed?
"Just make'em big enough" ?
Could someone measure a commecial tunnel portal for steam/diesel loks so I would have something to go on, please?
Threre will be 3 single track portals and 2 double track portals...
I think we may have gone overboard with the tunnels....
This is our first attempt at model railroading so any advice is welcome.

btw. "we" means me and my wife...

I attach a pic from the mock up of most of the scenery elements, what is missing is the Wineyard/mountain on the right that will enclose the tracks.

 

[Mountain Man]

Go to NMRA's site and check out the Standards and Recommendations section. tunnel portals are based on the Standard Loading Gauge, and IIRC, there is a diagram you can access that shows how the measurements are derived.

Prototypically, tunnels are dug no larger than they have to be to keep costs down.

 

[Tone]

Thanks

I'll have to dig deeper on the NMRA site then.
I know the layout isn't much in the area of "prototype" but the main idea behind it was to create a "living furniture" for the den. It's going to enclosed in glass (with access doors on at least 2 sides) to protect it from the pets and occasional spills that will happen on a table...

Thanks again.