Tunnel portals: all you need to know

02 August 2022
Tunnel entrances can take many different forms. We look at widely-available model examples from manufacturers, and build a model railway tunnel card kit with the beginner in mind.

Railway tunnels conjure different memories for individuals, but a common trait is the obscurity that they offer. Obscurity creates intrigue, and intrigue is something that we’d all like to create on a model railway.

From a modelling perspective, a tunnel should be justified. With time, effort and money invested into creating or purchasing models, it would seem odd to want to hide them from view in a tunnel. However, what a tunnel takes away in views of trains, it can add in scenery.

If used to advantage, tunnels can improve layouts, hiding fiddleyards or control panels from view. They can also introduce complexity to scenes through changes in scenic heights.


Modelling tunnel portals

The best tunnels on layouts are considered during the planning stage. Adding a tunnel to an already-created layout can create difficulties in adapting existing baseboard heights, or changing the scenery above to blend with that already in place.

Tunnels vary in style, shape and purpose. From ornate stone castellated buttresses and arched entrances, to stark angular flat poured-concrete slabs. Regional differences today are less pronounced than in the past, when railway companies or land owners would construct using accessible materials, or in-keeping with local architecture, dressing stonework or constructing from brick accordingly.

An important aspect to make look right is the portal. Scratch-building is an option, and particularly useful if modelling a specific tunnel entrance that can’t be easily adapted from the wealth of tunnel portals now available. Luckily, for modellers who don’t have scratch-building skills, portals can be purchased from your local model shop or online, for OO or N or O scales.

A tunnel’s shape depends on where it’s located and its intended use. Modern high-speed tunnels sometimes have an oblique portal, combined with upper vents to reduce noise created by differences in pressure. In the UK, with our comparatively low line speeds under 125mph, this isn’t such a problem.

Tunnel sizes vary wildly, too – some barely sufficient to cope with modern rolling stock, particularly if susceptible to icicles forming, others created large enough that overhead catenary could be installed with a little lowering of the track bed.

Common materials used in tunnel construction in the UK are dressed stone, engineering brick in its variations of blue or red – sometimes both if repairs have taken place – and pre-formed or poured concrete. In most cases, the same materials are used to line the inside of the bore and protect against soil erosion from above though water ingress, falling rocks, or simply the tunnel collapsing. It’s possible to see a decorative dressed stone fascia applied to a more mundane brick internal structure to improve appearances, too. In more recent years, shotcrete – concrete fired at walls under pressure to form a layer – has also been used to line tunnels. Let’s look at the most widely-available types of tunnel portal for model railways.

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Model railway tunnel portals

Faller 120570 [HO]

We often see HO (3.5mm:1ft scale) items repurposed on British OO gauge (4mm:1ft scale) layouts, and thanks to the generous continental loading gauge, this duo of tunnel portals from German manufacturer Faller is no exception. Injection-moulded in plastic, their assembly requires just four components to be glued using a solvent adhesive such as Humbrol (AE2500) Liquid Poly, Revell (39604) Contacta, or EMA Plastic Weld.

Castellated tunnel portals are a rare sight in the UK, but seeing this one reminded me of the Redhill tunnels near Thrumpton in Nottinghamshire. One facing north, and constructed in the 1830s, is surrounded by trees and vegetation, and rarely sees much light in winter, leading to excellent weathering opportunities for the more adventurous modeller.

Measurements inside the lowest (and narrowest) section of the tunnel are 134mm, with a clearance height of 106mm. Its overall exterior height is 159mm and overall exterior width, 190mm. Inside the tunnel, moulded plastic spigots are provided to support a card or Plastikard tunnel wall. Owing to its size and the scale of the stones moulded, this kit could be used as a single-track tunnel portal for 7mm:1ft scale layouts, too. A great option for modellers seeking more ornate architectural detail, though surround it with castellated turrets for best effect. 

Viessmann (5097) [HO]

Here’s a product that I discovered while researching for this article. Made by Viessmann, this tunnel has LEDs that appear to fade into the distance through the clever use of mirrors. Its packaging and the fact that it has a strip of printed and flexible road included suggests that this is for cars only, but at BRM, we like to think outside the box.

The outer stone fascia is moulded, and though not wide enough for a double-track line in OO gauge, could be used as a single-track. Two mirrors are closely aligned, the foremost semi-transparent. Four LEDs sandwiched between these provide light, which shines back and forth, seemingly disappearing into the distance. Most railway tunnels in the UK aren’t lit unless there’s engineering work. And, because you won’t be able to run trains through the tunnel anyway – there’s a pair of mirrors in the way – why not pose figures in hard hats outside this tunnel? This tunnel doesn’t need to lead anywhere on your layout. Perhaps it’s a solution to that awkward wall blocking your siding? It’s sure to spark interest with onlookers.

LEDs are protected by a diode on the positive connection, and a 150 Ohm resistor for the negative connection. The unit can be connected to a 10-16V AC or a 14-24V DC or DCC output. The portal measures 92mm at its narrowest at the base, with a maximum internal height of 66mm. Overall outer dimensions are 96mm in height, and 164mm in width. Ideal for adding interest to a scene.

Model railway tunnel portals in N

Peco (NB-31) [N]

Featuring in the manufacturer’s Lineside range of kits, this pair of N gauge tunnel portals are possibly the easiest of ‘kits’ to assemble, each with just three constituent parts. Injection-moulded in plastic, there is little to no flash to remove, making these ideal for first-time modellers or those that want to indulge in a rapid layout build. They’re very cost-effective, too.

Behind the fascias, we find plastic lugs to support a card or plastic inner structure (not provided), while prominent raised stone detail makes painting easier. The retaining walls – if angled, correctly – won’t sit flush against the portal wall, leaving an unrealistic gap. For best results, file the back of the retailing walls to an angle, using a coarse file. Internal dimensions of the tunnel at the lowest point are 33mm. The opening measures 41mm at its highest point. Overall dimensions without retaining walls are 83mm in width and 55mm in height. Though designed for 2mm:1ft scale layouts, this kit could also be used on TT (3mm:1ft scale) layouts, if a little tight, or as a pedestrian underpass on 4mm:1ft scale layouts. Great for lower budgets.

Graham Farish Scenecraft (42-228) [N]

Blue engineering brick is rare on layouts. Perhaps it’s because many plastic kits moulded in red plastic to look like bricks make modellers automatically think of red brick? Graham Farish’s Scenecraft range has a number of layout-ready items painted in blue engineering brick, but the detail on this double-track tunnel portal is excellent. Its simple shape, devoid of buttresses – two mere concrete-colour painted stone caps and inset parapet wall detail – is offset by the separation of the portals, each having its own arch.

Retaining walls in the Graham Farish range can be used in conjunction with this item for longer tunnel exits, or a run along a cliff face, for instance. The single-piece cast resin item measures 90mm overall, with a maximum height of 49mm, while each tunnel portal measures 25mm internally at its lowest point, with a maximum internal height of 32mm. Considering the detail in the brickwork and the time saved in constructing from scratch, this portal is certainly value-for-money.

Model railway tunnel portals in OO

Bachmann Scenecraft (44-292) [OO]

For beginners, or those with a more generous budget, Bachmann’s Scenecraft range offers excellent ready-to-use buildings and structures. Its Single Tunnel Portal joined the range in 2018, and offers another style of tunnel entrance for the modeller, this time, predominantly in brick. Cast as a single resin piece, we see an impression of a rendered stone or concrete base and upper parapet, while Flemish bond-cast brickwork is painted to simulate blue engineering bricks on buttresses, and red engineering brick for the central section. Buttress caps are moulded with an angle, as would be the case to shed water more easily. Water is a common enemy of structures and can cause great damage when it rests in masonry joints, freezes and expands.

At 253g, this is the heaviest of the structures reviewed. Though negligible at this level, a layout with a significant number of resin structures will weigh more than card equivalents, and baseboard strengthening might be required. Weathering is carried out effectively; a black spray around the tunnel mouth, with a black wash applied under the parapet dentil cornice. A subtle detail is the central decorative keystone. The tunnel at its lowest part measures 50mm wide, with a 62mm-high entrance. This structure is compatible with other retaining walls in the Scenecraft range, while a Double-track Tunnel Portal (44-228) is also available in the scale. Owing to its cast nature, the inner walls of the tunnel are modelled and painted, to a depth of 9mm. Joining an inner tunnel of your own design to this, and painting to match might require a little patience – there’s no ‘lip’ behind to easily secure an internal card or Plastikard sheet. Otherwise, a detailed and great layout-ready solution.

Wills (SS59) [OO]

One for the plastic kit enthusiasts, Wills’ single-track tunnel mouth offers modellers a chance to build a detailed brick-style portal. Injection-moulded in red plastic – making damage less visible if painted a red brick colour – its assembly requires parts be freed from sprues with a craft knife, filed flush with a sanding stick and glued with a solvent adhesive. The retaining wall edges are tapered in this kit, so that they provide a flush fit against the tunnel fascia wall. Further details include a taller parapet wall than most of the other kits reviewed, and two buttresses to complete the retaining walls. The tunnel mouth has an elliptical shape, with an entryway measuring 61mm in width at its lowest point, and a maximum internal height of 61mm. Overall external dimensions of this portal – minus its winged walls – are 133mm in width and 108mm in height. Moulded supports are provided behind the portal for a card or Plastikard tunnel former of choice. Being moulded in plastic, my choice would be to use Plastikard sheet for the tunnel interior, bonded with a solvent adhesive for strength before installing on the layout. Detailed, and ideal if you’re seeking a structure with an irregular-looking Flemish bond brickwork – observe reality, it does happen!

Hornby Skaledale (R8510) [OO]

This resin cast pair of tunnel portals joined the Hornby range in 2019. Cast to depict English bond brickwork, a simple thin buttress detail frames the sides, while a low parapet wall runs along the top. Pre-painted to represent weathered brick, further enhancements could see the coping stones along the top painted in a non-brick colour, and weathering inside the tunnel mouth. As with Bachmann’s pre-cast item, no rear guides are provided for a tunnel interior, though this model lacks the interior brick detail seen on Bachmann’s version. That said, it’s at a much lower price point.

Hornby’s tunnel portal offering for OO gauge in single-track form is generous. However, despite an entryway of 63mm in width at its lowest point, and a passageway height of 68mm, as with most of the tunnel portals reviewed here, there’s little room for catenary unless raised by at least 10mm. A great solution for time-starved modellers on a budget, with room to customise or further enhance.

Noch (58248) [OO]

One of the largest tunnel portals reviewed is Noch’s HO scale stone-effect model. Despite its 3.5mm:1ft scale, its generous size means that OO gauge track can fit comfortably underneath, with room for overhead catenary if required, too. Moulded in a dense foam, it is slightly flexible, though a tunnel portal of this design shouldn’t conform to the landscape, rather the other way around. Stamped in the keystone at the top, we see the date 1910. Either side of this at the same level are two stone culverts – an opportunity to highlight with gloss paint to create the illusion of water, adding green mould underneath, perhaps?

The overall width of this portal at its lowest point is 113mm, with an overall maximum internal height of 97mm. The sizes of stones used are perhaps a little large for 4mm:1ft scale – though it’s not uncommon to see some pretty large stones used in masonry – so I feel this portal is better suited to 7mm:1ft scale layouts as a single-track item. The size of the mortar courses and amount of relief in the undressed stonework would help here, too.

Metcalfe (PO243) [OO] 

This die-cut card kit is ideal for beginners. Pre-printed on sturdy card sheets, designed to be laminated during construction by the modeller, this provides the builder with two single track tunnel portals. Included in the kit are retaining walls with buttresses, which can be angled to suit a specific location. The assembled kit has a tunnel height of 85mm, tunnel depth of 95mm, and width at its lowest point of 70mm.

Further kits in the Metcalfe range employ the same style of stonework, and so can be used in conjunction with this kit to create more complex portals. Similar kits are available in the Metcalfe range for double track tunnel portals, with N gauge variants, too.

How to make a model railway tunnel portal


Almost a rite of passage, I feel that all modellers should build at least one card kit in their lifetime. Many find them addictive, however, particularly Metcalfe kits with their ease of construction and concise printed instructions. Parts and even cut lines are clearly labelled.


Read instructions before starting, sometimes a few steps ahead to get a feel of what is required. Instructions are to instruct, but aren’t necessarily the only way to construct the kit, particularly if you want to modify yours to fit an awkward location. Parts are freed cutting along scorelines using a clean blade on a craft knife. You can use a steel rule to guide the blade if your hand struggles to cut straight lines, though you’ll still have to free the curved portal freehand.


Sturdy grey card is in plentiful supply with Metcalfe kits. The inner carcass is formed by folding a sheet along pre-cut lines and gluing supports into place. The two centre-most supports are integral and folded back, the diagonal supports are additional, hence are glued. Busch (7593) glue is a fast-drying white glue, ideal for card kits.


One of the wonderful things about modelling is its ability to remind us of the laws of physics – that, and a continual lesson in logic and common sense. This piece of card wants to spring outward because of its fold line, even though it has been folded over-centre. The solution to keep it in place while other modelling ensues is a cup. Had the cup not been heavy enough, fill it with water – simple!


Metcalfe’s tunnel portal is the only one from this group reviewed to feature an interior tunnel wall. It’s a great addition because, as locomotives are increasingly fitted with LEDs, this unpainted and perhaps un-modelled section of your layout might be shown. Adding one of these to other tunnel portals isn’t difficult and pre-printed card, paper, or painted Plastikard sheet can be used. Here, small cuts are made to separate the outer fixing tabs.


With the inner face and outer arches in place and glued using Busch (7593) glue, the outer tapered support columns are added. These are handed, the outer sides having wider walls that wrap around. Card kits are easily assembled by accident with corners at obtuse angles. Pushing these into square is achieved simply using the edge of a rule, while the glue dries.


Much of Metcalfe kits obtain their strength through bracing and lamination because card is a flexible material. Large unbraced areas can warp over time too. Lamination is highlighted with the assembly of the upper stone wall section, to which a sheet of the instructions is dedicated.


A combination of double or triple laminations and wraps is used to produce the wall which sits on flags. When cut, card can sometimes distort under the pressure of the knife blade. The result is that it is more difficult to glue square and straight. Always straighten components by eye first, twisting or bending them by hand, then check against a rule or on a level surface before finally gluing them. These won’t further distort before glue sets.


With upper wall added, Metcalfe’s PO243 single-track tunnel portal has enough detail to satisfy the eye. The winged retailing walls can be angled to suit your terrain, while additional walls provided perpendicular to track, extend the tunnel face, providing a back wall for terrain or vegetation. The kit could be further enhanced with self-adhesive textures from the likes of Redutex, or customised with brick papers for an engineering brick appearance. Recommended.

Find out more

If you're looking for further advice to help develop your next model railway project, the articles below will help...

Model Railway Buildings: A Beginners Guide

Model trees: all you need to know

Ballasting model railway track: All you need to know

How to make realistic shop windows 

How to build and detail a card kit

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