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What about doubling the length of airfields in order to shorten the time it takes for a plane to roll on the ground after landing and before takeoff. The plane could take off from the middle of the air-lane and when it lands it can turn off in the middle, in order to minimise the driving time to and from the terminal. Why don't we see this and what does it take to achieve it?

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    $\begingroup$ Smaller planes can already do this at larger airports, it is known as an intersection takeoff. And depending on where the destination is at the landing airport, we can turnoff the runway earlier once slowed down vs going all the way to the end of the runway. It all depends on the size/speed of the aircraft; a large jet needs more rolling time both for takeoff & landing with all that momentum vs a small 2/4/6 seater that can be airborne and landed/slowed down in well under 2000 ft. $\endgroup$ – CrossRoads Nov 28 '18 at 13:34
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    $\begingroup$ Or you could have two shorter runways side-by-side... Pretty sure that is very common throughout the world... $\endgroup$ – Ron Beyer Nov 28 '18 at 15:12
  • $\begingroup$ Cost is a good reason not to do this. Instead of having 2 9,000' parallel runways that are potentially useful simultaneously, you have 1 18,000' runway that you're only using half of. $\endgroup$ – FreeMan Nov 28 '18 at 18:41
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The cost is that it would required a runway twice as long.

Airports already take up enormous amounts of land. Designers try to build airports near major centers, so taking up twice as much valuable land for longer runways near a major population center is a huge cost.

The longer runways also need to be cleaned, maintained, and snow-plowed.

That is a lot of cost and difficulty just to reduce taxi-time by a couple minutes. After one has taken a 2 hour cross-country flight, 5 minutes of taxi-time is not a point of concern.

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    $\begingroup$ Denver International Airport was designed to minimize taxi times as well as allow for simultaneous parallel operations when necessary. The runways are laid out in a 'pinwheel' with one end near the terminal. With a northerly wind you can land on 35L and 35R and roll out near the terminal on the east. Takeoffs can use 34L and 34R which start near the terminal on the west side. In bad weather you can use 34L and 35R to get the separation for parallel ops though the 34L aircraft will have a longer taxi. $\endgroup$ – Gerry Nov 28 '18 at 13:39
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    $\begingroup$ Anyone who has landed at DIA may question that it minimizes taxi times. I've often heard it joked that planes land at the Kansas Border, and drive in to Denver. $\endgroup$ – abelenky Nov 28 '18 at 15:06
  • $\begingroup$ 5 minutes taxiing for 200 passenger compares to a cost of say USD 1300, regardless of how long time the flight takes. Is there a calculation somewhere about savings and costs? $\endgroup$ – David Jonsson Nov 28 '18 at 16:22
  • $\begingroup$ @abelenky i said it was designed to - I didn't say it was successful. But it does apply a concept very similar to what the question proposes. And taxi times at DEN are typically better than DFW. Flying between DFW and AUS, it wasn't unusual to have taxi times at DFW greater than the flight time. $\endgroup$ – Gerry Nov 28 '18 at 16:48
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Not quite to the same extent you have in mind, but when you are able to have a staggered set of runways, they will try to arrange it so that the "landing" ones have the roll out area near the terminal, and the "takeoff" ones have the threshold near the terminal.

Let's take BWI as an example. In an south/east flow (takeoffs and landing heading south/east), all traffic will take off on 15R, right next to the NW end of the terminal. All traffic will land on 10, with the exit from the rollout a little bit after the runways cross.

Or IAD, in a North flow, most landings will happen on 1R and takeoffs on 1C.

NAS (naval air station) Lemoore is another sort of example of this - kind of a little split because of the structure of the ramp, but if it was one terminal, in a NW flow you'd have all takeoffs on the N runway and all landings on the S runway.

Put another way, if you have a 9000 foot runway, in your scheme you'd need to make 1 18000 foot runway, but it is at least twice as efficient to have 2x9000 ones, even if it increases the taxi time, and some of that can be mitigated by the staggering above.

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Notice that most airports are square-ish. For various reasons, it's usually a lot easier to get a compact parcel of land than a long, thin one. In particular, aviation authorities really don't like roads going under runways, so the airport as a whole creates problems for the highway system around it; double the length of the runways and those problems get much worse. In the old days, a square parcel was used to provide several (intersecting) runways at different angles, but many have been rebuilt to have parallel (and thus simultaneously usable) runways in the same compact area; taxi times might be a bit longer, but overall throughput is much, much higher.

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