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How to build Functional Underpasses with FLUPs (NAM)

Started by Chrisim, May 17, 2010, 02:56:19 PM

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FLexible UnderPasses (FLUPs) are included in the NAM. It's a modular system for building functional underpasses. This is a tutorial to help you getting started.

Please see the topic FLexible UnderPasses (FLUPs) for a description of FLexible UnderPasses (FLUPs). Also, please post bug reports, requests for further developments, questions, answers and discussions in that topic, and please use it also to share pictures showing your FLexible UnderPasses.

This tutorial consists of the following chapters:
1 Build a Road Underpass below Rail
2 FLUPs Ramps
3 FLUPs Underground Route Pieces
4 Tips and Tricks for using FLUPs Puzzle Pieces
5 Check whether your FLexible UnderPass works
6 Build a Tram-Avenue Underpass
7 Underground Tram Pieces
8 Underwater Underpasses
9 Overhanging Lots to visually hide underpasses
10 Lots as Ramps
11 NOB Sunken GLR
12 FLUPs Tunnel Gates
13 Bus and Tram Stops for FLUPs Underground Routes
14 How to develop FLUPs Custom Tile Sets

Many thanks to z and Jonathan for their support creating this document


This chapter describes how you can build a simple road underpass crossing below a rail line. Assume you have a road/rail crossing:

and you wish to replace it by an underpass.
Use the bulldozer to remove the road/rail crossing:

Select the FLUPs - Flexible Underpasses (available with the installed NAM)

This will select the "Ramp for underground Road". Simply plop it onto the road as shown in the next slide:

Move the cursor to the other side and plop it onto the other road end. You may have to rotate it using the HOME or END keys. Be careful - HOME / END are also used to select other ramps, so avoid selecting a onewayroad underpass.

Reconnect the rail track stubs by dragging rail over the gap:

Select the FLUPs - Flexible Underpasses and use the TAB key until the Rail FLUPs pieces are shown. Use the straight (not diagonal) pieces in this case. Use the HOME or END key to rotate the piece until "Straight underground route perpendicular under straight Rail" is displayed - its preview shows a red line perpendicular to the rail track:

Plop it:

The Road under Rail Underpass is complete.

In similar ways you can build other underpasses such as the following road underpass under rail and highway. When the "FLUPs - Flexible Underpasses" rotation ring is selected, use the TAB key until you find the highway pieces. You may have to rotate with the HOME or END key to select the correct highway underpass piece.


The previous chapter showed how to build a road underpass using a road ramp. There are more ramps for other traffic networks. When you select the FLUPs - Flexible Underpasses, the road ramp is usually the first selected piece. Use the HOME or END key that will first rotate the selected road ramp, but then switch to another ramp, the one-way entry or exit ramp:

Click TAB once, and you can select (using HOME/END) between the following ramps: Street, Tram (GLR), and the Transition ramp from Tram-in-Road to Tram below Road:

Another TAB click, und you can select the Avenue ramp, Tram-Avenue ramp or the Transition ramp from Tram-Avenue to Tram below Avenue:

A third TAB will allow selecting the street tunnel (for use on a flank of a hill) or the pedestrian stairs.

A RHW-FLUPs ramp is included in the Real Highway Mod, a non-core NAM product available as separate download:

So, in summary there are ramps for

  • road
  • one-way
  • avenue
  • street
  • tram
  • tram-road to tram below road
  • tram-avenue
  • tram-avenue to tram below avenue
  • RHW
  • Pedestrians (Sims)

However, there is another "ramp" to FLUPs underpasses: Network Lots. As shown in chapter "Bus and Tram Stops for FLUPs Underground Routes", normal bus stops work also for FLUPs underground routes and act as "ramps" for pedestrians. The same applies to other network or transit enabled lots - they can also act like ramps for FLUPs underpasses.


This chapter gives an overview of the underground route pieces that connect the ramps (presented in the previous chapter). You need to plop the underground route pieces in the correct way to obtain a fully functional underground network.

Underground route pieces are available for a variety of surfaces. The first image shows those with road, street and one-way road at the surface. The tiny manhole covers indicate the presence and direction of the underground routes. The bottom row of single pieces shows straight underpasses perpendicular to the surface road (street and one-way road). The upper row with two pieces each shows diagonal underpasses under surface road (street and one-way road).

Although the diagonal pieces look like right angles, they effectively form diagonal paths and can be used as both, diagonal or curved underground routes.

When you have selected the Route Query tool and hover the cursor above a FLUPs puzzle piece, a semi-transparent texture is displayed. A red straight line indicates an orthogonal underpass route, and a curved red line (as displayed on the image above) indicates a curved or diagonal underpass route. A diagonal underpass (upper row) consists of two single tile puzzle pieces, each being curved.

There are underground route pieces crossing below avenues and ground highways (orthogonal and diagonal):

There are many underground route pieces below rail (from left to right): orthogonal underpass perpendicular below orthogonal rail, diagonal underpass below orthogonal rail, orthogonal underpass parallel below orthogonal rail, underground 4-way junction below orthogonal rail, underground T-junction below orthogonal rail, orthogonal underpass below diagonal rail, diagonal underpass parallel below diagonal rail, diagonal underpass perpendicular below diagonal rail, and diagonal underpass parallel with offset to rail, and diagonal underpass perpendicular below diagonal rail.

There are orthogonal and curved (diagonal) underground route pieces below various types of ped malls, transparent surfaces and green grass surfaces.  For the pavement, transparent and grass textures, there are also underground 4-way and T-junctions.

There are perpendicular underground route pieces below tram-avenue and normal tram (GLR), and diagonal route pieces below normal tram (GLR).

There are orthogonal and curved (diagonal) underground route pieces below curved surface road:

and also below diagonal surface road (watch the manhole covers that indicate the direction of the undergound route):

There are six underground puzzle pieces that are reserved for custom surfaces. These are not included in the NAM download. The image shows the FLUPs custom tiles "set A" published at the LEX. The included surfaces are parks, ways and Pegasus' stream (required as additional dependency). Information on how to prepare additional sets is included further down in this tutorial.

There are two FLUPs puzzle pieces in the CAN-AM rotation ring that allow building perpendicular orthogonal underpasses below canals.

If you have installed the High Speed Rail (HSR) mod, you will find the following underground puzzle pieces in its rotation rings: perpendicular below GHSR, diagonal below GHSR (consisting of two curved pieces), parallel below GHSR, and perpendicular below HSR (with and without pillar):

If you have installed the Real Highway (RHW) mod, you will find a ramp and several underground puzzle pieces perpendicular below RHW networks:


TAB - HOME - END: Navigating for FLUPs Puzzle Pieces
Use the TAB or SHIFT-TAB to cycle through the different types of surface pieces (rail, highway, ...). For one surface piece, e.g., rail, you can get different subsurface connections by cycling or rotating with the Home/End keys. You can cross the rail track (left picture), you can put a curve (middle) and you can have road parallel below rail (right):

Curved and Diagonal FLUPs Connections
You can create diagonal underpasses by plopping curved pieces next to each other:

Although the diagonal pieces look like right angles, they effectively form diagonal paths and can be used as diagonal or curved underground routes.

There is no piece for parallel road below road/street/..., because the traffic simulator would not recognize the depth difference and car traffic would jump between surface and underground roads. It is a bug of SC4 that we cannot correct, and in order to prevent it for FLUPs, we don't offer such "parallel" road pieces.

Do not build the ramp on very steep ground
Plopping a ramp will flatten the ground to a certain degree, but you will probably get a visual glitch when the ground was too steep.

Flatten the ground by selecting the grey street and plop four single tiles next to each other (plopping, not dragging). After bulldozing you can plop the ramp properly. Flat ground is required only for the ramps, but not for FLUPs puzzle pieces.


Let's assume that you created a FLexible UnderPass, but you are unsure whether it works correctly. There are several possible checks to verify whether there is a continuous connection without gap between the ramps.

1. First look for the tiny manhole covers that indicate the underground route.

2. Select the Query Tool and move the cursor above a FLUPs underground route piece. The text will tell "GLR/tram or Elevated train or FLUPs" and a red line will show the direction of the underground route on the tile. Yellow tram symbols along a grey line indicate tram only underground routes (see the next chapters).

3. If you are still unsure about the integrity of your FLexible Underpass system and if you have installed the Extra Cheats Plugin, move the SC4Paths above ground and use the DrawPath cheat to visualize them. First exit the game, download the attached zip file, extract the file zNetworkAddonMod_FLUPs_SurfacePathsTest.dat and move it into your folder My Documents\SimCity 4\Plugins\Network Addon Mod\Plugins. Restart your city. FLUPs SC4Paths are normally at -10 m (this means below surface), but this file moves them to +10 m (above surface) and therefore you can visualize them using the DrawPath cheat. Do not forget to remove the file zNetworkAddonMod_FLUPs_SurfacePathsTest.dat when your test is complete.

For this example of a road underpass under rail, you can see road paths in green and pedestrian paths in blue on the far ends. Along the ramp, you can see road paths dipping upwards (without this cheat, they would dip downwards into the subsurface being invisible). No pedestrian can enter this road ramp. Ignore the small gap where SC4Paths reach the ground, this gap is due to the ramp model extending slightly above the ground and hiding the SC4Paths.

On the single tile FLUPs underground route perpendicular to rail, you can see many paths: green for road (therefore, the underpass is continuous and will work), blue for pedestrians and red for light rail.

Each FLUPs underground route piece contains all these paths at a height of 10m below surface, and therefore, they can be used for any type of underpass. Remember that the type of underpass is defined by the ramp. The green road paths are pointing in both directions, and therefore the FLUPs underground route pieces can be used also for one-way road and avenue (and street and RHW) underpasses.


Avenues and tram-avenues are networks that are two tiles wide. This chapter shows how to create a tram-avenue underpass, and the same system applies for an avenue underpass.

With the FLUPs from previous NAM versions, it was only possible to build road, oneway and avenue underpasses. Now it is also possible to build underpasses for tram (GLR) and pedestrians. In UDI mode you can drive a car or a tram through the underpass.

Let's build a tram-avenue underpass below ground highway. The first steps are to plop the tram-avenue ramp twice and to drag a ground highway:

Select the FLUPs - Flexible Underpasses and use TAB several time until the underground route piece for ground highway is displayed. Plop it

and plop it again next to the first

and you have a functional perpendicular tram-avenue underpass below ground highway:

In a similar way, you can build an underpass below diagonal ground highways. Note the two single tiles in the upper left and lower right - these are FLUPs puzzle pieces with transparent surface required to close the connections for this diagonal case.

You may note in UDI that tram automata show a strange side-jump when entering into the tram-avenue underpass. This cannot be changed easily for technical reasons. Normal automata (without active UDI) do not show this jump because they are invisible below the ground level.

Note: If you had build an avenue underground route with a 2009-NAM, and you wish to replace it with a tram-avenue underground route, it is not sufficient to replace the avenue ramp with the tram-avenue ramp. You also need to bulldoze the underground avenue route and replace it with new (2010-NAM) puzzle pieces, otherwise trams cannot pass.


There are some new tram-only underground pieces available that differ from normal FLUPs underground route pieces. They can be recognized in the preview by the yellowish tram display along a grey line (instead of the red line typical for normal FLUPs pieces):

These tram-only puzzle pieces are required for tram ramps as shown here:

This is a functional tram underpass that allows trams to exit from the tram-in-road without crossing a road.
The following tram underpass pieces are available. Most of them are 4way junctions for the underground tram.

The piece in the lower left corner shows the yellowish tram display along a thick grey line that identifies tram-only underpasses.

Note that you do NOT have to connect the underground tram on all sides. The first image shows a road T-junction at the surface that is a 4way underground tram junction, but only two of the four are connected. The reason is that this way there are less puzzle pieces in the rotation ring that is already quite long.

There are further tram-only underpass puzzle pieces for surface junctions with avenues, as in the following example:

The underground tram junction does NOT have to be connected on all sides (above image), but of course you can:

For tram-only under avenue, the following pieces are available:

Again, underground tram junction can be connected, but you do not have to. So you can build underground curves or T-junctions if you wish.

Of course, it is also possible to build underground tram junctions below avenue

or transitions

These are the underground tram-only puzzle pieces for surface avenue:

Again, you do not have to connect all sides of the underground tram junctions.

The modularity of the system allows much flexibility to build various tram underpasses:

Of course, you may also choose to keep the tram on the surface. The equivalent to the previous image is:


You can create underpasses below a CAN-AM canal as shown in the first posting, and you can create underpasses below streams using overhang lots or the FLUPs custom set A, but you can also create underwater underpasses (e.g., a tunnel to an island). Cars or trams can cross through such tunnels (also in UDI), and ferries can cross them (right image). However, you cannot cross them with a bridge.

(click for larger images)

If you wish to create a subsea underpass, select the water pollution map - water will not be displayed and it will be much easier to plop the puzzle pieces. You can tell the direction of the underground route by the manhole covers (drains), or by selecting the Route Query tool and hovering the cursor above a piece.

In UDI mode, you may observe a fascinating set of diving automata:


There are a few overhang lots for the game that can be used to visually hide underpasses. Underpasses can pass below such special lots, e.g., Diggis' streams and ponds. This picture explains:
First create a normal underpass (upper left) and don't forget to connect both ramps with an underground route piece. Here a transparent surface piece was chosen and the tiny manhole covers indicate the presence of the underground connection.
Then, select the overhanging lot (upper right), plop it (lower left), and watch UDI using the underpass (lower right picture). Some overhanging lots (e.g., Pegasus' ponds) require that they are plopped prior to the underground route connection puzzle piece.


You can use transit-enabled lots as ramps to convert traffic from one network to another type. For example, a subway station typically converts pedestrians to subway users, but here the station looks like a ramp:

The animated GIF image shows (from left to right) a tram (GLR) transition to subway (by the SFBT team), a tram-in-road transition to tram under road (by the RTMT team) and a tram-avenue transition to tram under avenue (also by RTMT). All are transit-enabled lots and not FLUPs puzzle pieces. This may be confusing because there are also FLUPs ramps that look almost exactly the same.

Assume that you have a tram-avenue line around a landmark.

As major you decide to move the tram below the surface. You have two options. You may use FLUPs ramps (from the FLUPs rotation ring, not the lots!) and connect them with FLUPs underground puzzle pieces

or you may use TE-Lots as transition from tram-avenue to subway and back

and connect both transitions by subway:

This method has the advantage that the subway can be dragged independently of the surface conditions, which is very useful in busy cities. The disadvantage is that you cannot drive with tram automata through the subway in UDI mode.


Using NOB's Sunken GLR transit-enabled lots (re-modded, it will be re-uploaded soon at the LEX), it will be possible to build a sunken GLR (tram) network. The following images show only the transition lot of NOB's Sunken GLR (tram), but there are more lots included in the set for which the same rules hold.

If you leave a gap between two lots and drag a road across,
you need to connect the two lots to get a functional sunken tram system.

One option is to connect the two lots by subway:
with the drawback that you cannot drive through in UDI with tram automata.

The other option is to connect the two lots with FLUPs underground route pieces:
If there is enough traffic on your route, you will see tram automata continuing from lot to lot. And of course, you can drive through the underpass with tram automata in UDI mode.

You will observe that normal tram automata stop at each lot for a while before continuing on their track. This is similar to tram stations, and we cannot change this characteristic of lots. And we cannot change NOB Sunken GLR lots to NAM puzzle pieces because the grass texture would hide the GLR tracks located below the surface.


This special piece, a FLUPs Tunnel Gate, is new in the May 2010 NAM:
This Street Tunnel Gate is the first piece of its type and was created by the NAM Team member Toja. Hopefully he will create further pieces for future NAM versions.

This tunnel gate must be plopped on the flank of a 10 m high hill. You should ask: how do I create a 10 m high hill?
A 10m Raiser Lot is included in the "NHP Hole Digging Lots by Shadow Assassin" available at the LEX.
Another option is to use the "FLUPs Ground Lifter 10m" that you find attached to this posting. It works like Smoncrie's original ground lifter, except the height change is 10 m:

Let's build a street underpass below the railway and through the valley. Select and plop the FLUPs Tunnel Gate:

Select the FLUPs street ramp and plop it on the other side:

Select and plop the FLUPs underground route piece perpendicular below rail:
and the FLUPs underground route piece below transparent surface:

The fully functional underpass is complete:
You may plop the FLUPs street ramp directly next to the rail tracks. I inserted the extra tile with transparent surface to avoid a steep slope, but this is your choice - with all the modular pieces of the FLexible UnderPass system (FLUPs), you have the choice.

You can connect FLUPs Tunnel Gates with FLUPs ramps or TE-Lots as you like. These are described earlier in this tutorial.

The idea of FLexible UnderPasses is to use them in flat city areas or zones with limited height variation, but nothing prevents you from creating a FLUPs underground route below the mountain surface (from left to right in the foreground, marked by manhole covers):

However, this route is too steep for my fire brigade in UDI mode - it is stuck.  :D
It's better to use the valley for the street or to drag a tunnel through the mountain.


Normal bus stops work for FLUPs underground routes. The next picture shows a road ramp into a long straight underpass indicated by the tiny grey manhole covers on each tile  border. The other end of the underpass is not shown on the picture, but it is also a road ramp. With road ramps on both ends, this underpass is used by cars and busses.
I plopped a bus stop next to the underpass and connected it by road.
The Route indicator shows what happens:
In addition to car ("Auto") and bus traffic along the underpass, there are some busses stopping at the bus stop. It does not matter that the bus stop is visualized above surface, because it also works for the underground traffic. Some pedestrians (violet arrow) leave the underground bus and continue by normal (overground) bus to their destination.
The same applies to other network or transit enabled lots - they can act like ramps (or bus stops or tram stations) for FLUPs underpasses.

Of course, it would be nice to have special visually matching bus / tram stops for FLUPs underground routes, but they have not been created (yet?).


There is presently one published FLUPs Custom Tile Set (Set A). The set acts as interface between the Network Addon Mod (NAM) and special underpass lots. This chapter provides the information how to develop further sets. It is for advanced modders, not for beginners.

There are six FLUPs custom tile puzzle pieces included in the NAM. Their size is one tile. Their instance IDs are 0x53e61800, -900, a00, -b00, -c00 and -d00. Load the file FLUPs_Custom3_Plugin_SFBTparktrail$$$.dat from FLUPs Custom Tile Set A in the Reader:
It is the third custom tile in the set and has the ID 53e61a00. There are six texture files in FSH format - five are for display in zooms 1-5 in the game. Unlike lots with base and overlay textures, there is only one texture in five zooms. You have to merge all into one texture before converting to FSH files (using the SC4Tool and option "transit texture"). Manhole covers shall mark the FLUPs pieces - here is the overlay as a transparent PNG file for use in your graphics program:

The other FSH file is for the preview:
The preview should show the red stripe and manhole covers typical for FLUPs pieces. Here is the overlay as a transparent PNG file:

There are two LTEXT files (with English and German descriptions). Depending on the language of your game, you can add further languages giving different group IDs for various languages as described in the tutorial LTEXT - Language Text Files (How to make multilingual buildings and queries). If you need a German translation, please ask in the forum Translation Requests.

Finally, there is a T21 exemplar in this case. When your new custom tile piece exists of a texture only, you do not need it and you can simply delete it.
When you are converting an existing lot into a FLUPs custom tile, and the original lot contains props, you will need this T21 exemplar.
In this case, the Lot Configuration exemplar of the original lot contains prop lines (LotConfigPropertyLotObjectData properties with 0x1 as first value). Simply copy them into this exemplar (and reindex LotConfig). In some cases, the props need to be rotated by 90 degrees. The easiest way to do this is to rotate them in the Lot Editor on the original lot and to copy the rotated props over. Please see the tutorials on T21 exemplars for more details (How to create T21 exemplars (Swamper77's way) and How To Create and Modify T21s (Xyloxadoria's Way)).


So to clarify on the custom sets, it's only possible to have one set installed at a time? And should a second custom sets be restricted to private use, or is publishing with a warning about conflicting with the SFBT set acceptable?


Yes, it's only possible to have one custom set installed at a time. If you develop a new set, please publish it. A general warning about the risk of a conflict with other sets is a good idea!


Ok, thanks for the info. I'll be creating a second set to integrate RMIP with FLUPs with the following 6 tiles:

Taxiway piece, light
Taxiway piece, dark (i.e. 747 style)
Taxiway piece, turf edge
Ramp piece, light
Ramp piece, dark
Airport turf

Many of these pieces already consist of a base and overlay, but since they're likely to be placed next to a piece without an overlay the manholes should come out ok.

One last question; all of those pieces are UDI enabled for airplanes by placement of the 1x1x3 runway gnome prop, will it work ok to place that with the T21 or will it conflict with the vehicle UDI of the underlying FLUPs system?

Edit- Also, when making the textures in SC4Tool, is it just a regular texture or should the transit texture option be used?


Awesome! I was just coming here looking for some answers and found this freshly posted. It answered all my questions! Thanks so much!


What a great job Chrisim.. thanks for all the careful documentation.