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Tunnel Clearances

January 2003

How wide and high should I make my tunnels?

There are a couple of issues here: modelling in 16mm/ft isn't an exact modelling scale. Depending on what you're trying to achieve, it could be anywhere from 19:1 to 24:1 scale, and the prototypes you're modelling might be different sizes anyway. Also, if you've got long coaches, and curved tunnels, you'll need to allow greater clearances as the coaches swing out on the corners.

Below are some suggested tunnel sizes from various people in the 16mm community.

Chris MacKenzie 7" High 6" Wide
John Rogers 6.5" 5"
David Rhodes 7" 6"
Les Darbyshire 7" (max 8") 6.5"
Paul Backhouse 7.25" ?

Barry Reeves

Go as big as you can.
Say 6" wide and 8" tall. Much too big all round [...] Big holes are easier to pull trains out from too.

John Rogers

Brandbright and Roundhouse both have a maximum 6.6" height and 5.2" width. I would think that 8" x 6" would be OK for straight tunnels & bridges. [...]
Extra width should be allowed for tightly curved bridges. IMHO, curved tunnels are a very bad ideal indeed.

Bert Coules

The only places where clearances are a problem are at the tunnel *mouths*. Why not make the actual tunnels as large and accommodating as your garden permits? Why not engineer your tunnel mouths so that they are removable? That way, when someone rolls up at your meeting with an unexpected monster, they can still get round your line. It would make rescuing stuck stock a lot easier, too...

David Rhodes

Irish stock will dictate the largest loading gauge.
I allow 7" from top of running rail to underside of parapet, and minimum of 6" track base width.

Ian Barker

...has some clearance problems with tunnel mouths that are tapered in at the bottoms. The tunnel mouths had to have the lower side cut back at the bottom, to clear running boards.

Les Darbyshire

The tunnel mouths on my 32mm line are 7" high above rail level and 6.5" wide. They were waisted inwards at the bottom, but I have cut them vertical. The actual tunnel is 7.25" high, and the roof is removable paving slabs. I had to take the slabs off the other day to allow a DJB logging loco through (another half inch would have done it) and once had to remove the tunnel mouths (but not the slabs) for a County Donegal railcar. Otherwise, everything has fitted.

Dudley Hubbard

Seeing as my line uses Mamod track with some curves made tighter and is extremely tiny (even smaller than John Rogers' VSGR) I guess I'll build any tunnels to fit my stock and warn any visitors of my loading gauge.

Stuart Flitchfold

For those in 16mm 180 and 85 both in millimetres from rail top and centres respectively.(7.1" high x 6.7" wide)
It even covers shh.....G scale, with 220 and 85 millimetres (8.6" high x 6.7" wide) I think, but 24 hours and a recent bottle of wine has made this all a bit hazy. I might just go with 220 and 110 on my line. (8.6" high x 8.7" wide)