I heard that from runway 18R-36L the taxi time is around 20 minutes, I heard that this runway was built and is used mainly to reduce noise pollution, but what reasons are there for the length of the taxi?
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$\begingroup$ Unanswerable unless you can put an exact dollar value on noise reduction, people's time, and jet fuel (hint: it's only possible for one of them). $\endgroup$– Nuclear HoagieNov 19, 2018 at 17:57
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$\begingroup$ The answer is a matter of opinion. Those who place a greater premium on less noise would argue it is worth the extra fuel. Those who don't would say it's not. $\endgroup$– TerryNov 19, 2018 at 17:59
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$\begingroup$ I can understand that people living near airports want to reduce noise, but does it worth the amount of fuel the airplane burns and the extra CO2 emissions. $\endgroup$– pedro galindezNov 19, 2018 at 18:01
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1$\begingroup$ Q: "Why is the railway station so far from the town?" A: "To be close to the railway." The question here is incorrect. It should be, "Why was the runway built so far from the passenger terminal?" $\endgroup$– TransistorNov 19, 2018 at 22:54
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2$\begingroup$ "Why is the taxi time 20 minutes?" Because the taxiway is long. "Why is the taxiway long?" Because the runway is far away. "Why is the runway far away?" To reduce noise pollution by moving it further into a rural area, in EHAM's case. It makes more sense than building a new major airport further out in the country. $\endgroup$– 0xddNov 20, 2018 at 15:24
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1 Answer
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Firstly, I'd like to make clear that the particular reasons for the placement of the taxiway are not all publicly disclosed, and there are undoubtably multiple factors involved. After looking at the airport in Google Maps, I notice a couple things. (Excuse the large picture, explanation below!)
1) Physical & Geographical Limitations
There is a pre-existing highway in between the runway and the rest of the airport. The runway could not be placed closer to the airport in the current direction without either removing the highway, or bridging over the highway (as the taxiway does). The highway would be unlikely to ever be removed, due to the extreme cost of removing pre-existing infrastructure, nor would they like to bridge a runway over the highway. Runways require a fair amount of maintenance in comparison to taxiways, and including a bridge in the design of said runway would drastically increase the cost and complexity of maintenance.
Looking at the map, there is absolutely nowhere to place a runway of that length and bearing without drastically engineering a solution. Beyond that, there does not seem to be anywhere within the "block" of the main airport to create a runway of that size, regardless of bearing.
2) Noise Abatement
The fact that the runway is in a less dense area also means that aircraft on approach would cause less noise disturbance for the populated areas nearer the core of the airport. In fact, for the northern approach, there are not many developed areas - it is primarily open fields. Aircraft are only allowed to takeoff to the north, and land from the north, on this runway, to avoid overflying the populated areas to the south of it.
3) Other Potential Factors
The above reasoning we can be relatively certain about. However, there may be other contributing factors, such as ground quality. As there are rivers and streams nearby (including the one that the taxiway bridges), much of the ground may be more difficult to build on, and require more expansive foundations.
Conclusion
Regarding a taxi time of twenty minutes, there is certainly potential for a taxi of that length, but it is not due to distance. The distance is not anything extraordinary compared to many other "Hub" airports. The time is likely substantially increased by the fact that, if runway 18/36 is in use, they will likely be told to taxi around 18/36. The primary reasons for the creation of this runway, cited by the planning committee, were arrival/departure capacity and noise abatement.
While this is certainly not a very efficient system, it is certainly the only solution I can see to provide a runway of that size. There could be various improvements, but cost is the overarching factor.
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$\begingroup$ "including a bridge in the design of said runway would drastically increase the cost and complexity of maintenance" it might, but if you look at the east end of 09/27, you'll notice that it bridges over the E19/A4. Not only that, but the aiming marks are directly on the bridge which means that aircraft land there sometimes. $\endgroup$– FreeManNov 19, 2018 at 19:34
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2$\begingroup$ @FreeMan The A4 tunnels under 09/27 rather than the runway "bridging" over. You can see the terrain and the runway stay level.Presumably the runway does not rest directly on the roof of the tunnel, but there is bit of earth separation between. This puts the cost primarily on the highway operators, rather than the runway operators. It does not require much additional engineering in this fashion for the runway, while creating a bridge over the river and highway would require more engineering. $\endgroup$– M28Nov 19, 2018 at 19:43
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$\begingroup$ Not quite sure I follow you, @Matt. I would expect any road/aircraft interchange to involve the roadway going under the taxi-/run-way. While local soil conditions could make it it more difficult/expensive, I see no obvious reason (based on 30 seconds of scanning the aerial view on Google Maps - an obviously rigorous methodology ;) that the same type of grade separated crossing couldn't have been made for Rwy 18/36 and the N520. Thus shortening the taxi times and honking off the local residents who would have been displaced. $\endgroup$– FreeManNov 19, 2018 at 19:51
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$\begingroup$ @FreeMan If you zoom in on the highway, it has a river inbetween. This makes tunnelling much more difficult and costly, as they will have to hold back, or potentially redirect, the water. In the 3D view of the taxiway bridge, you can see that it is not very thick, which would not be sufficient for a load/force bearing runway. $\endgroup$– M28Nov 19, 2018 at 19:54
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$\begingroup$ @FreeMan Here is an image of the underside of the bridge: i.imgur.com/3wOTkeg.jpg $\endgroup$– M28Nov 19, 2018 at 19:56
