### Author Topic: Tunnel and bridge lengths and costs  (Read 553 times)

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#### Freahk

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##### Tunnel and bridge lengths and costs
« on: December 20, 2019, 07:34:03 PM »
Maybe tunnel and bridges and elevated ways should get a rework to make these rules unneccessary?
If we calculate the cost of a bridge depending on pillar height  pillar height and distance in between pillars, where pillar height scales linearly and length between these, let's say exponential, we would not deny people from building long bridges over deep water but we would make this inprofitable.
This also also roughly what happens in the real world: A short bridge over e.g. a road is quite inexpensive. Lengthening it by a few meters is no problem as long as we are not far above ground, we simply have to add pillars, so it scales roughly linear with length. However, it will become much more expensive as soon as we have a valley underneath, so we either neeed lo leave out pillars for a long distance and construct something else to get the required stability, or build high pillars down to the valley.

Same goes for tunnels: It is relatively inexpensive to build an open cut tunnel. Maintainance is also not too high and it scales perfectly well with tunnel length. However, when you have to have to dig the tunnel deep under ground, this wil be much more expensive as ensuring security rules will become more and more expensive the deeper you are down and the longer the tunnel.

Additionally placing pillars under water is even more complicated (and expensive) than pillars on the ground. I guess the same goes for tunnels under the see as you can't just build an emergency tunnel upwards.

I guess I should create a request for this?
« Last Edit: December 21, 2019, 12:47:02 AM by jamespetts »

#### jamespetts

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##### Re: Re: Bridgewater-Brunel no. 1 - Great Britain sized map (no. 2)
« Reply #1 on: December 20, 2019, 10:00:43 PM »
Re: Bridgewater-Brunel no. 1 - Great Britain sized map (no. 2)
« Reply #487 on: Today at 19:34:03 »

Quote (

Yes - this is a separate issue from how the server should be set up.

This is not likely to be a high priority for my own efforts for some time, as it is likely to be complex to implement and will need very careful consideration to make sure that it can balance properly, especially as some bridges can cope with unlimited depth without change in cost if they are short enough (e.g. girder bridges, single arch bridges) whereas some bridges will scale only linearly in cost with length but exponentially with height (bridges supported by pillars) but other bridges will have complex relationships between cost, height and length (e.g. cantilever bridges, suspension bridges, multiple arch bridges).

Until we can simulate the relationship between cost and height (and its relaitonship with the relationship between cost and length) in a sensible and coherent (as well as realistic) way, we are better not simulating it at all.

#### DrSuperGood

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##### Re: Re: Bridgewater-Brunel no. 1 - Great Britain sized map (no. 2)
« Reply #2 on: December 21, 2019, 12:35:59 AM »
Maybe tunnel and bridges and elevated ways should get a rework to make these rules unneccessary?
This is not the topic to discuss this.
If we calculate the cost of a bridge depending on pillar height  pillar height and distance in between pillars, where pillar height scales linearly and length between these, let's say exponential, we would not deny people from building long bridges over deep water but we would make this inprofitable.
Not realistic. There is no exponential scaling with costs in real life as it is largely down to materials and labour which is linear.

In real life one cannot bridge between Europe and America. This is because not only is the Ocean several kilometres deep on average, but the ocean condition is hazardous to bridge structures. The reason one cannot tunnel under the ocean is because the tunnel would need to cross several geological fault lines and the only source of fresh air would be entrances at either end. Such bridges or tunnels would also be several thousand kilometres long so either take hundreds of years to construct or so many resources that single countries cannot afford to fund it, even if it were possible.

Simutrans Extended already simulates this with bridges. Water that is too deep cannot support viaduct bridges and can only be crossed by bridge spans. Bridge spans are finite and realistic.

The only issue is tunnels. The realistic solution would be that tunnels have a maximum length between ventilation based on tunnel type, where ventilation is specified as tunnel entrances, special structures or stops which have structure on or above the ground plane. This would allow hundreds of kilometre long underground tunnels for servicing cities while preventing one tunnelling across the ocean.

Until such feature is implemented, please keep tunnel lengths to realistic limits. For example in 2016 the longest tunnel under a sea/ocean one can build is ~60 km.

#### jamespetts

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##### Re: Tunnel and bridge lengths and costs
« Reply #3 on: December 21, 2019, 12:47:49 AM »
I have split this from the discussion about the game server as this is a different topic. There is merit to Dr. Supergood's suggestion; but this will take a long time for me to code, and will have to join a large queue behind other priorities.

#### Freahk

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##### Re: Tunnel and bridge lengths and costs
« Reply #4 on: December 21, 2019, 02:53:09 AM »
let's say exponential
That was an example, which for sure needs more careful consideration. However, linear is not realistic. Bridges scale linearly in length when their main span is constant, which is the case for viaducts but not for bridges over rivers or valleys.
If you want to scale in length and pillars get longer, you will start increasing the bridge span in between pillars because these become expensive. However, you can't increase the span withouth strengthening that section. That will lead to non linear cost scale. Additionally about pillars, you obviously can't use the same pillar strength for a 100m high bridge that you would use for a 5m high bridge, thus not even pillars will scale linearly with height.
So, maybe it is not exponential scaling, which was just an example as mentioned, but it is for sure not linear and definitely not constant, which is currently simmulated in simutrans-ex.

Currently, a 9 tile long bridge across a deep valley will cost exactly the same as a 9 tile long bridge a half-height above ground and if you want to build it one tile longer it will suddenly be simply impossible.
Both of this is far from realistic.

Also, I don't want to bridge from Europe to America, which is a very extreme example, but let's say I want to bridge the Great Belt or from Awaji to Kōbe.
Alternatively in Simutrans terms: I don't want to build a bridge from one edge of the map to the other, but when I have a fairly small part of sea in between two contients and demand in between these is high enough, I simply want to build a fairly expensive bridge that is a few tiles longer than the current fixed maximum.

The issue about tunnels is roughly the same, for sure with different parameters.

We don't have to span across anything and we don't have to build pillars, but we have air conditioning and we need a security concept, thus long spans of tunnel in between emergency exits and air conditioning stations will reqire additional underground infrastructure as emergency and air conditioning tunnels, simmulated as increasing per kilometer costs.

These special constructions required for air conditioning and emergency exits should for sure be more expensive, the deeper the tunnel is under ground, and it should not be possible to place these under water at all.
I am not even sure if the player should place these manually at all or if it should simply be simmulated as increased cost.

#### DrSuperGood

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##### Re: Tunnel and bridge lengths and costs
« Reply #5 on: December 21, 2019, 09:34:49 AM »
That was an example, which for sure needs more careful consideration. However, linear is not realistic. Bridges scale linearly in length when their main span is constant, which is the case for viaducts but not for bridges over rivers or valleys.If you want to scale in length and pillars get longer, you will start increasing the bridge span in between pillars because these become expensive. However, you can't increase the span withouth strengthening that section. That will lead to non linear cost scale. Additionally about pillars, you obviously can't use the same pillar strength for a 100m high bridge that you would use for a 5m high bridge, thus not even pillars will scale linearly with height.
Ultimately this is all limited by physics and technology. It is not possible to have a bridge with pillars above a certain height. Like wise it is not possible to have bridges with a span larger than some amount. Even if modern materials allow their construction, they might not be safe at such heights.

The current limitation with viaducts was a hacky work around to prevent players bridging across the map, which I was tempted to do early during the 1800s on the bridgewater brunel server game. The long term intended solution is that viaduct bridges would take into account the height of the sea bed beneath them and allow building over non-shallow water as long as their support pillars can reach. The discussed implementation would treat under water height different from above water so as to prevent early viaducts from entering deeper water (due to technological limitations) and more modern ones possibly supporting longer height under water than above water (due to water density). Such feature might also support various costing levels for support lengths, potentially implemented via lookup table for fine or realistic price tuning. As such this is currently a low priority feature.

#### jamespetts

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##### Re: Tunnel and bridge lengths and costs
« Reply #6 on: December 22, 2019, 02:44:28 PM »
I should note that there is already a system that prevents bridges with pillars being built on all but the shallowest of seas - has this stopped working?

#### Freahk

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##### Re: Tunnel and bridge lengths and costs
« Reply #7 on: December 22, 2019, 03:43:43 PM »
No, that still works.

However, as mentioned, I think the current binary behavior is kind of unrealistic and frustrating.
What I mean with binary is, either it is possible to build the bridge (in case of pillar bridges: if no deep water underneath, in case of non pillar bridges if length<maxLength), otherwise it's not possible.
If it is possible, a tile of bridge will have constant cost, no matter the terain underneath or the span of the bridge.

In reality, if a connection above anything is desired, it will be checked if it is possible and most often it is possible but a matter of finances (and protesting inhabitants), so even though possible, some projects won't get built.
Further, a bridge type that may be quite expensive for small bridges could scale better for a specific case where a huge bridge is needed.

In simutrans-ex, we have expensive and less expensive bridge types. These differ in weight and are either spanning type or pillar type.
Terrain does not matter at all for bridge cost, it is simply per-tile-constant.
Additionally, the game engine will either tell us "that bridge is possible" or "that bridge is impossible". It will never tell us "it's possible but pretty expensive".

#### jamespetts

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