Northbridge and Budleigh Junction - Double Decker

[Corbs]

So it begins.....

 

Chris AKA Northski has recently returned to railway modelling, he and his father (my grandfather) had a large layout back in the day but it all went into storage during a house move and never came out again.

We've been refurbishing a lot of the old locos and stock to bring them up to more modern standards using bits from broken or scrapped other locos - here's the CLINIC thread.

 

Well, these need somewhere to run, so permission was gained to re-use my old room (which has seen many a railway) as the new railway room. When I was small the two kids bedrooms were extended into one another with built in wardrobes. The issue with this is that it makes it harder to fit a railway in. 

Sooo out came the wardrobe...

 

Now, we've been through what must be more than 50 track plans and proposals. We still don't have one but we have a list of things to have on the layout, and we were in a bit of a vicious circle of track plans and revisions, so we eventually decided to make a start and work it out later.

 

First, MDF (ply will be used for the main and scenic boards but we went with MDF for this). Screw a nail in the centre and measure 48" circle

 

Then measure the tuna

 

Choppy choppy

 

 

Vorsprung durch choppy

 

A few more bits

 

Installed on legs - the fiddle yard boards on the left are re-using the reclaimed frames from Chris and Bob's original model railway, with new ply tops. Also pictured is a happy Northski.

 

"Hold on lads, I've got a great idea.... ermmm...."

All caught up - the first level of the helix in place. The baseboard underneath will actually hold a reversing 'dog bone' loop for the end of the fiddle yard, coming across in front of the doorway.

 

 

The helix is wide enough for 3 tracks and we are keeping the middle section open in case we need to get in there and sort out a derailment.

The outer track is 4th radius, meaning that the climbing trains have the easiest curvature to deal with to give them a fighting chance. I imagine extra weight will be added to the locos wherever possible.

 

Next we need to start fixing down some track on the ground and 1st floor levels...

Edited January 9, 2023 by Corbs

[Corbs]

Righto, here comes the learning CURVE (sorry).

 

My experience of laying track may as well be zero, it's either been too long or I can't remember doing it at all. In fact this is possibly the part I dread the most and may well be the reason none of my layouts ever got finished.

 

For the helix, we are going for a cork underlay glued with PVA to the MDF, then the track is being pinned through the cork and the baseboard. The fiddle yards will likely use a cheaper underlay.

 

We traced the track we needed onto the cork and cut it out (excuse dirty fingernails)

 

This hopefully gives an impression of how it will work now the 2nd radius helix has been secured, as well as the 'ground floor layer'.

 

 

The blue and grey coaches are on the end of the 'dog bone' which will exit roughly where the box of screws is and traverse the outside of the room, through the fiddle yard and joining the helix via the 'lead in' board where the white box of track is (top left), then up, up, up the helix before exiting onto the scenic area atop the fiddle yard, where the red mug is bottom left.

 

The first layer of the helix has now been set, rising 10cm every rotation. Descending trains use the 2nd and 3rd radius loops and climbing trains use the 4th radius.

 

This is incredibly track-hungry but we are really excited about it!

Edited December 29, 2022 by Corbs

[Corbs]

So, some pretty swell work done yesterday (cracking on with it later today, too).

 

We managed to get all levels of this helix in and mounted, track laid...

 

 

Ready for testing. 

 

First up was my little 0-4-0ST 'Perseus' which is battery power/radio control, doing haulage tests. Over one minute to do a full circuit!

 

But it made it!

 

 

So, one of the main known issues with helixes is that they are extremely difficult for steam locos to climb, a combination of not much weight and fewer driven wheels than modern diesels.

It's intended that the layout will be able to represent late pre-nationalisation all the way up to large logo, but we had always intended a 4 coach limit for the steam-hauled trains.

With the helix in place we could now run tests to determine the height.

The helix in these pics has a 12cm climb in between layers.

 

First up was the Mainline 43xx mogul. This is quite weighty and has traction tyres on the rear driving wheels. It went up with a minimum of slippage on load 4, on the 3rd radius line (which will actually be the 'down' line, with the 4th radius being the 'up'.

 

So emboldened by this we tried the fairly new-ish Hornby Black 5, which was disappointing, slipping to a stand on load 3 on the 4th radius. It looks like it is just too light to 'dig in' as when you rest a weight on the loco, it grips and sets off again.

 

We then lowered the helix to have 8.5cm climb in between layers. This means that it's now very difficult to re-rail stock, although the Black 5 could make it up on load 3. Possibly there is a balance to be struck here so it may be raised again.

 

The others:

 

Duke of Gloucester - good, load 5 all the way to the top (much heavier than the Black 5)

Limby Class 50 (all wheel drive Hornby chassis) - load 14 all the way up, could probably have taken more as it weighs a ton!

Lima class 47 - surprisingly good, big weight inside despite only one driven bogie - load 12 (I think)

Lima class 37 - slipped with load 10, too light

Airfix large prairie with Hornby motor - load 5 all the way to the top (airfix chassis is one huge weight)

Hornby-chassis large prairie - load 4 (oddly this one doesn't slip but instead just stalls - needs investigating)

OLD Hornby-chassis pannier - load 4, pretty good result!

Hornfix 31 - load 6 - needs more weight

Tender drive Castle - easily climbed up with load 5 - traction tyres on the tender to the rescue

 

More testing later today....

 

Edited December 29, 2022 by Corbs

[Corbs]

Not quite so much progress today (funny how building the layout slows down when you can run trains up and down) but more testing showed that the Black 5 is low on adhesive weight. We packed the smokebox with some lead sheet, glued some to the keeper plate and made up some sections to hide inside the cab. It can now at least haul 4 coaches up the incline. By comparison the Hornby 8F hauled 5 up with not much trouble. Possibly a bit more weight, maybe the smaller wheels and extra driving pair help?

 

The first of the underslung weights.

 

 

These hide in the cab - any crew members will have to be shorter than usual to fit in!

 

 

What was impressive was the good old Bachmann Pannier making short work of taking 4-5 coaches up the helix. Superbly made little things. The Hornmann Pannier (pictured) manages about 3. I think we are going to look at reducing rolling resistance by changing wheelsets and adding pin point bearings to the coaching stock. The old airfix stuff rolls all the way to the bottom if you place it at the top, but the other coaches will go round half way and then stop.

 

 

We've now reset the helixes to be at 9cm height intervals, allowing for more 'fiddling space' in case of derailment. Lots of adjustment has taken out a few flat spots to keep the gradient consistent, previously it was very flat-climb-flat-climb all the way up, so locos would pick up speed on one side and then stall on the other. Now it's more of a steady climb.

 

Next up is taking the fiddle yard line across the room on a lift-out section. The two ends of the dog bone are on at the top and bottom of the helix, so this end passes around the room under the layout. This involves going over the remains of the built-in cupboard.

 

 

Then we cut the baseboard to be used for the lift out section - the idea is to build it as a lift-out-able board, then perma-lay the track across it, then cut the track so it fits together properly when the board is in place.

 

 

 

 

 

 

 

Edited December 29, 2022 by Corbs

[Corbs]

Yesterday we got some time in on the megalayout after a break to France.

 

After reading about other people's experiences with MDF we decided to try sealing as much of the helix boards as possible. Dilute PVA was used for this. Chris had the ingenious idea of using a radiator brush to get the bits in between the tracks. Seen here pulling faces at me.

 

Nicely sealed now and should help toward longevity.

 

 

Another task was to properly lay in the lower storage sidings, able to hold a 2 coach and a 5 coach train respectively. Added a nice sprung bufferstop (salvaged from the original layout nearly 30 years ago) to the longer siding. Not fitted any lighting here yet so it's a bit dark!

 

 

 

 

We also sealed the main lower layout board (which is ply) onto which the helix comes on to.

Chris has decided to leave the lift-out section until last, which means we can build the lower station sooner and get trains running! This lift-out section is only for the dog bone anyway, so the fiddle yard area will work without it.

 

 

Edited December 29, 2022 by Corbs

[Mikkel]

What a project. The helix looks great, in a thousand years it will cause much head scratching among archaeologists!

 

I agree about the Bachmann panniers, but that nice slow sclimb of Perseus was a real pleasure to watch. Keep it coming please, gents.

[Corbs]

Thanks Mikkel! It's certainly one heck of an undertaking.

A few hours spent yesterday on the megalayout. As has been mentioned before, we have a rough idea and a basic trackplan for the main bits, but we're kind of making the rest up using trial and error. It's not everyone's preferred method but we were so sick of making endless amounts of trackplans and just wanted to work out what everything looked like by mocking it up in real life. Probably not the best method but at least it gets the layout off the page and into the world!

Originally the lower level was going to all be fiddle yard, but we are taking the opportunity to add more scenic area to the layout and vary operation without cluttering it all up too much, so there will be a lower station. This is exciting as we can incorporate an MPD and the capacity to stop trains in the station, attach a banker and shove it up the bank. The Lima 4575 seems to be excellent at this so it may well be going through the works for a tart-up next!

 

So here we are trying to work out what we can fit on the bottom layer. We really really want a turntable. The Heljan one looks nice.

Lining paper used for drawing on. All the essentials are here.

 

 

Here we are with a rough plan. Two-track main line through the station, the goods/banker down line (inside of the helix) goes around the station and also provides access (via a trailing point) to the MPD.

 

We really want the impression of trains travelling through the landscape, so the main line goes diagonally across the board. The MPD is at the front as it's interesting and provides a visual break with the trains going behind. We're going to modify the front of the board around the turntable to fit the thing in as it's ruddy big. The station will be a few cm higher than the MPD, meaning less of a climb for trains going up the helix, and providing variation in terrain and a rising view as you look over the layout.

Here the UP line is blue, DOWN MAIN red, and DOWN SLOW yellow, with the shed lines in fetching purple. The entrance to the helix will be masked by a station building/overbridge combo with stairs down to platform level.

 

Round the corner is the entrance to the fiddle yard, same colours apply. To enable bankers to leave the shed and enter the banker holding siding (extreme left), there's a single slip over the DOWN MAIN which also gives DOWN SLOW access to the same fiddle yard. The yard goes on to enter the lower dog bone at the end of the room.

The area at the front will either become a goods yard or plain scenic area, with a diagonal scenic break heading bottom left to top right.

 

 

Edited December 29, 2022 by Corbs

[Corbs]

Soooooooooooooooo.....

 

As previously mentioned, the lower board was going to be a simple fiddle yard, but I've watched the 'Lickey Incline' episode of Railway Roundabout far too much and managed to convince Chris he needed the MPD at the bottom of the helix to hold the banking locos, and that while we were there we might as well add a scenic section....

Anyway things do tend to snowball a bit and today Chris became the owner of a Heljan turntable.

 

Here, we are trying to work out how long the platforms should be to accommodate a 4 coach train. The idea is that the station building is on an overbridge, which also acts as a scenic break before the helix. The fast lines will be raised above the others and we are using the lining paper to mark out the plywood for the raised section.

 

 

As can be seen, the turntable is too wide to fit on the current baseboards. These are built out of the salvaged remains of The Old Layout, but some changes need to happen.

 

 

We've added a reinforcing brace and a mid-way leg underneath, then cut out the cross brace. The extension braces will rest on this wider beam, taking the weight through the legs rather than the corner brackets.

 

 

Pop the turntable in, it fits! Which is just as WELL. In the background you can see the plywood we are using to raise the station area.

 

 

Chris is going to be working on the rest of the extension board and prepping the uprights for the top layer.

 

The newly weathered and detailed 47 hangs out with the Duke on the helix.

 

 

Edited December 29, 2022 by Corbs

[Corbs]

Whilst we managed to make good progress yesterday, I spectacularly failed to get many 'in progress' photos, so here is the end result.

 

The extension is installed and reinforced, the ply sides make it incredibly rigid. Also visible is The Big Leg, which is part of the support structure for the top deck (Budleigh Junction).

 

The station that will occupy this site will be Northbridge, a grimy industrial area. Bankers are kept here to assist trains tackling the incline out of the valley. After passing through the tunnel, ascending trains arrive at Budleigh Junction in the lovely British countryside. This connects Northbridge to The Rest of The World. Bankers detach in the station and descend the bank on the down slow, returning to the MPD.

So far we've found Lima 4575 prairies to be excellent bankers, so expect to see some stabled here. I have a feeling that post-1968 a Brush Type 4 may be used for the same purpose.

 

The area I'm standing in will be the operating well. 

 

[Corbs]

We want this layout to last, and we want the helix to work. We've tried to understand as best we can as to why helixes sometimes fail, and why they get a bad rep. One problem is baseboards sagging causing the track to become uneven. There is a lot of weight being placed on some very small areas. The best time to tackle these issues is now, before we have built the top deck or added scenery.

 

Chris has set to with making some extra support bracing. The nuisance of a door has been removed and may be re-hung the other way around (coincidentally the way it was originally hung). Amazing how much bigger the room feels.

 

 

This photo shows how the brace will support the helix upright.

 

[Corbs]

Quite a productive day yesterday, though it was one of those which will probably look like not much has changed!

We tore up the lower dog bone and sidings, this will be replaced by a 2/3/4th radius triple loop allowing us to store trains like the HST easily and a better route to the lift-out section across the doorway (keeping the lift-out section as small and simple as possible is key).

 

As we had dialled down the amount of height each helix loop climbs in order to make it easier for certain trains to ascend, the overall height of the helix had come down by a fair bit. We'd traced the outline of the final circuit before we installed it so adding another loop was fairly easy.

Here it is being measured up.

 

Down at the entrance to Northbridge Station, we altered the helix lead-in by cutting and remounting it as shown, this will allow tracklaying to continue into the station and shed area. Re-railing ramps are to be added at the foot of the helix as it's not easy to reach.

It's held in place from underneath as well as the sandwich clamps.

 

Here's a shot from underneath showing the substantial reinforcement we've added to the helix, making sure that each vertical rod is supported so the MDF can't bend as much.

 

Finally, we played Tidy Up The Nursery and it felt good, Chris will be able to carry on with tracklaying and sealing the top of the helix, and the station approach, then we can start building the open-frame baseboards for the upper station soon!

 

 

Edited October 29, 2018 by Corbs

[Corbs]

Chris has been a busy bee.

 

The baseboard on the top section of the helix has been painted. Chris has added some extra cork strips to add cant to the curve, illustrated here with three Mk.1s.

This is where the line emerges into the daylight at the top of the helix as trains approach Budleigh Junction.

 

Meanwhile, down in the grimy town of Northbridge, Chris has started laying the main line through the station (on the raised section next to the MPD).

 

Buddy was interested.

 

 

 

Ready for the first train! The Hornfix 31 does the honours. There are 3 side by side rerailers at the base of the Helix to help prevent accidents on the hard to reach bit.

 

 

[Corbs]

One of those strange situations where we've done quite a bit of work but one photo sums it all up.

 

As part of adapting the fiddle yard into a more scenic area, Chris dropped one of the boards down so there is some variance in layout height.

 

The radiator was always going to be a hindrance, it's necessary to heat the room but we don't want it damaging the track/layout, so a ply shroud has been built, we'll likely paint the inside with white gloss to reflect the heat up and out. It's clamped in at the bottom and is easily removable. The outside will be disguised as warehouses.

 

 

 

This is an industrial area and the main lines will be on a tall overbridge spanning the valley floor. Where the trackbed widens will be an embankment with retaining wall.

Top left will be the holding siding for the bankers, and the fan of sidings next to that is the start of the fiddle yard proper, the yard throat will be ballasted. Originally we were planning to use curved points but they ended up using more space than medium range points used with 3rd radius curves. The single slip allows DOWN SLOW Goods trains using the inside track of the helix (and avoiding the station) to rejoin the DOWN Main, and for bankers to get out of the MPD and into the banker siding.

Edited December 29, 2022 by Corbs

[Martin S-C]

How about lining the interior of the radiator shroud with metal cooking foil?

[Corbs]

Yes, that should be good at reflecting the heat and avoiding warping.

[Corbs]

More news from Northbridge as we progress towards getting the fiddle yard throat installed.

Chris has added a strong reinforcement to the viaduct so that there is no flex in it. We'll need to use some surface mounted point motors but they should be fairly unobtrusive amongst all the retaining walls etc.

 

Remember that this was originally a plain fiddle yard area so we are backpedalling quite a lot, the upper area will be of open framed construction.

 

 

 

Working out a nice smooth curve transition to avoid the set-track look coming out of the station. We cut a section out of the raised ply to enable an easier downward slope.

 

I was desperate to try out the Garratt's haulage capacity on the helix. 16 coaches was the maximum although plenty of wheel slip involved!

 

 

 

 

(the stalling at the end was due to a lot of PVA on the track which we cleaned off after, stupid YouTube was supposed to trim the clip but it hasn't!)

Edited December 29, 2022 by Corbs

[Corbs]

Well, we are overdue an update.

Since taking the plunge into DCC we've been adding wiring. Here's the NCE powercab plug and the bus running along the front of the layout.

 

The bus here running up the helix with droppers coming off.

\\

 

Here running under the junction on the bridge.

 

We've been laying the track connecting the station area of Northbridge to the fiddle yard via Bob Northey Junction atop the embankment.

Using flexi to get as smooth a curve we can within the space. Once in the fiddle yard we can revert to using 3rd radius curves.

 

Whilst train control will be DCC, we don't think we have the funds currently to fully adopt DCC for points and signals etc, but we can make up a control board with a contact pen for the different sections of the layout. For junctions like the one above, I would rather have a limited selection, rather than having to manually switch each individual point, and limit the choice to selecting a few 'routes'.

This means interlocking the points so they work together. To this end I've tried to draw up the following plan.

Bear in mind that the MPD is accessed from DOWN SLOW, so bankers will have to get from DOWN SLOW to SIDING, then later from SIDING to UP MAIN to buffer up to trains.

I've labelled the points A,B,C,D with C and D as both sides of the single slip.

Each 'route' is selectable by the circular button which corresponds with the options on the table (bottom left). This shows the combination of switch selections which each button needs to select.

 

 

I have checked this and believe it to be correct. This means that accessing the fiddle yard (off map to the left) is an 'either/or' option for the DOWN lines as they converge, but this selection does not affect the UP line.

The siding has 2 options - to connect to DOWN SLOW (to accept bankers from the MPD) or to connect to UP MAIN (to allow bankers to proceed to the train in the station).

Selecting UP MAIN allows the trains from the fiddle yard to be routed into the station.

There are no movements which require bankers to run wrong-line into the fiddle yard, or for UP trains to run wrong-line, so these are not presented as options.

 

I have also included signals SD1 and SD2 which control access from both DOWN lines. I do not want the signals to show green when the correct route is not selected, so they can be tied in to the interlocking system to switch at the appropriate time.

 

I hope this explains things. The aim is to make something simple to use even if it requires a bit more graft in the set-up, but is also cheaper than the DCC option which may replace this system in a few years time.

 

Edited February 26, 2019 by Corbs

[Corbs]

Yesterday, we connected the Down Slow up from the helix to the junction shown above.

Here it is partway through laying the MPD turnout, which goes to the turntable, the main sheds being located in the foreground. Point motor installed, frog juicer connected to the DCC bus. Every time we do it, it gets easier and more methodical, it's good to know that practice works!

 

 

Meanwhile, here is a very easy to understand wiring diagram for the interlocking.

 

 

Edited December 29, 2022 by Corbs

[Corbs]

While we now have the parts to make up the interlocking wiring for Bob Northey Junction, there was a looming task which we realised we were procrastinating about.

We can't construct the open frame top deck until the bottom one's woodwork and wiring is done, but the lift out section was giving us the heebie-jeebies. It's in the corner of the room so the track is curved, and immediately after the bridge, the track needs to descend to negotiate the dog bone under the helix and return trains to the fiddle yard facing the right way.

 

Yesterday we bit the bullet and set to work to build it.

A support structure for one side was built, and we worked out the correct height for the other. Came out level!

 

 

 

The lift-out section itself is a basic box that will be reinforced and clad in ply. To hold it in position, the supports have matching blocks of wood to act as a cradle.

Much careful measuring and sawing was needed.

 

 

 

The latches are located underneath. The intention is to have grab handles up and over the track to make it easier to lift.

 

 

Here are the supports with the lift out section removed, to show how they cradle it.

 

 

 

Edited December 29, 2022 by Corbs

[Northski]

Have started to add the baseboards, and rather overly engineered support piers, to the return loop that lies beneath the bottom level of the helix. The track is not laid yet but just checking that our calculations are correct and that we're able to accommodate a 3rd radius curve with a 4th radius siding. The picture also shows a 2nd radius siding leading back towards the removable section, which I've allowed for, but haven't decided whether to include this or not as yet. Plus a cup of tea, we drink a lot of tea. Sometimes that's all we do, guessing we're not alone in that. 

 

View beneath the helix showing the down line to the dog-bone return loop. 

 

Again the track shown isn't in its final place, but the shot shows how the gradients of the dog-bone return loop run the opposite way to those on the helix. 

 

This is the reason for the rapid change in height. To the top left you can see the main lines approaching the helix, which meant that the return loop/ dog bone needed to run beneath this. The inner track of this is the running line (3rd radius) and the outer line (4th radius) is intended to be for train storage.

 

General view from above, providing a pretty good idea of what's supposed to happen. The 5 storeys of the helix are independent of the return loop below it, but as a return loop was needed for continual running, placing it beneath the helix meant that no extra space was lost. 

 

I filled in the gaps once the support piers had been added. Probably should've done this before. This photo was taken under the new lights that I've just added. The original light was provided by a single pendant light fitting, and wasn't really up for the job especially in the helix area. The new lights are 2 x 40W 600 x 600 LED light panels which retail about £25 each, with the support housing around £10 each. The light provided is astonishing, if not a tad overkill, but if we start videoing any of the stuff we do, the light will be sufficient, albeit with liberal applications of Factor 50.

 

The old lighting

 

The new lighting panels during installation 

 

The completed lighting job. 

Edited June 15, 2019 by Northski

[Corbs]

Chris has been pressing on with laying the fiddle yard tracks recently.

 

The top two tracks are for bankers/pilot engines to assist on the helix.

 

Following advice from others, Chris has positioned the 3-way point as a trailing rather than facing point. The track on the right hand side is for programming and testing.

 

At the far end are the lines to the lift-out section. The two dead-ends are for auto trains and DMUs depending on the era to be played with. Due to the under-board area here being a storage cupboard, the point motors will be surface mounted.

 

 

 

[Corbs]

An update is required as we've done more since the last one.

The fiddleyard was redesigned slightly to give more loco and short train storage, as well as an extra through line.

 

We've done much of the structural work for the top level. The intention is to have this as an open frame baseboard with the track running on plywood, to enable us to make nice landscapes that aren't too flat.

With the uprights installed and fixed to the walls, the frame was constructed from 12mm ply, 150mm tall.

 

 

Most of the sections were different and required designing separately to work out which ones slotted into the others, and which way round the slots would be. Each piece had its own number.

 

 

The tolerances weren't very tight, the cuts being made with circular saw and jigsaw, then chiselled out. but it's mainly for locating them.

 

 

For the most part, the longitudinal pieces support the transverse ones.

 

 

The exception is the one above the turntable, which is supported by a transverse piece at one and and the windowsill at the other.

 

 

As you can see the room is a hive of industry at this point.

 

 

We also cut another helix layer to bring the track up to a decent height, now that we know the lowest scenery point.

 

 

The helix is made from MDF, sealed with dilute PVA.

 

 

 

Here's the room after a little tidying, which works wonders for the end of a session, because it allows you to focus, take stock, and enables future-you to start the next session a lot more easily, helping with momentum.

 

 

Note that the transverse and longitudinal pieces are held firmly in place with plastic brackets. The whole thing is very solid now.

 

 

In order to test out DC Analogue Interlocking System for the junction, I soldered up this board to the very detailed diagram I made a while back.

 

 

This will hopefully enable one switch to change multiple items, so that the user selects a track, rather than individual points, and it changes the signals accordingly.

I am hoping to run these points on a common negative, using the positive for switching (hopefully).

 

A busy few days but a great leap forward!

Edited December 29, 2022 by Corbs

[Ruston]

I've not seen this one until now, Corbs. I think the word for it is epic.

 

It reminds me of the layouts, owned by the fathers of a couple of my friends, that I would occasionally get to play with when I was about 7 or 8 years old. When I wished that my father would be interested in railways and not just cricket and beer.

[Mikkel]

I agree, it's great stuff Corbs. I'm pretty sure  if this was mine I'd end up in front of the helix all the time just watching the trains go round and round . Once it's all done, will it still be possible to stand inside the helix as per the first photos?

[Corbs]

Cheers both, certainly feels epic, though it's an interesting organic process as most of it is being designed as we go along with the bare essentials mapped out beforehand. Occasionally this does have setbacks (such as needing to add reinforcement to baseboards after they have been installed) but it is quite exciting as new ideas can crop up and be incorporated.

 

The intention with the helix once the 'top' is on is to have lighting inside, not only to watch the trains but also in case of derailments! There are 3 layers still to be added - one normal helix layer to bring the track level up, one for the double track main line circuit to go around the room, and another to bring the top of the 'dog bone' around so that the UP trains can turn around and back onto the DOWN line.