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Many airports have more than one runway. How should runways be built in order to achieve maximum usage and minimum delays?

Many major airports have most, if not all, parallel runways. Examples include LAX, DFW, and ATL.

In fact, Chicago O'Hare has been undergoing some major runway improvements, mainly to make the runways more parallel. This figure shows the before (mid-2000s) and after (completion date TBD) layout of ORD. Eventually, ORD is slated to have 6 parallel E-W runways, along with 2 SW-NE runways.

enter image description here

However, a crossing configuration is very common at airports with only 2 runways. Here is one example:

enter image description here

Are parallel runways more efficient, and smaller airports simply don't have space for them? Ideally, how should runways be configured?

Edit:

Additionally, what if we assume...

Case 1 - That wind isn't a factor?

Case 2 - That the airport location has exceptionally variable winds?

Case 3 - That space/airport footprint is an issue?

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    $\begingroup$ Surely the "efficiency" depends on what you're trying to optimize for: max throughput in the best wind, or being able to operate in many different wind directions without too much crosswind. $\endgroup$
    – Dan Hulme
    Commented Feb 7, 2015 at 17:50
  • $\begingroup$ Chicago seems to have the best of both $\endgroup$
    – rbp
    Commented Feb 7, 2015 at 23:36
  • $\begingroup$ Max throughput all the times. $\endgroup$
    – digitgopher
    Commented Feb 7, 2015 at 23:59
  • $\begingroup$ You should also mention configurations like of SFO with sets of parallel runways crossing each other $\endgroup$
    – Manu H
    Commented Feb 8, 2015 at 12:01
  • $\begingroup$ That's a lot of structures to be demolished at ORD, and a long ride in from 28L and 27R. $\endgroup$
    – FreeMan
    Commented Feb 9, 2015 at 19:03

2 Answers 2

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In order to increase the number of operations that can be handled at a runway, you want them configured so as to allow "simultaneous independent approaches," which means that the 2 (or more) runways can be operational without the need to coordinate between them.

The biggest factor is the distance between the two runways. The greater the distance between them, the less impact they have on each other, not just in terms of number of operations per hour, but also in terms of visibility minima for instrument approaches.

The other factor that needs to be considered is the wind, and as you can see from the Chicago airport layout, there are parallel groups of runways that effectively form a triangle, such that there is never a crosswind component that exceeds 30 degrees. The layout at Las Cruces, NM, which is usually very windy, shows the format better than Chicago, even though they are single runways:

enter image description here

The last issue is the type of radar available, and the faster the radar sweep, the less delay there is between the position of the aircraft and their depiction on the radar screen, allowing the controllers to closely monitor the approaches.

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  • $\begingroup$ Boston Logan is another excellent example of a triangle format. $\endgroup$
    – Vikki
    Commented May 1, 2018 at 2:25
  • $\begingroup$ But according to the OP Chicago has decommissioned one "side" of the triangle completely in favor of more East-West runways? $\endgroup$
    – Lykanion
    Commented May 17, 2018 at 16:30
  • $\begingroup$ @rdp: I am based out of Las Cruces NM. Are you based out of there as well? $\endgroup$
    – DLH
    Commented May 17, 2018 at 18:25
  • $\begingroup$ @DLH no, just dropped in a few years ago $\endgroup$
    – rbp
    Commented May 18, 2018 at 14:28
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Ideally runways do not intersect each other, and are all 4300 feet apart (laterally) to allow for simultaneous parallel instrument approaches. Denver is one such airport that meets all of this.

enter image description here
(flydenver.com)

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    $\begingroup$ This covers one aspect of "ideal", but totally misses out on dealing with crosswind. If you have a 50 mph crosswind, you can have as many parallel runways as you want but the throughput will still be 0. $\endgroup$
    – raptortech97
    Commented Feb 8, 2015 at 5:06
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    $\begingroup$ @raptortech97: DEN satisfies this as well; there are four north-south and two east-west runways, none of which intersect. $\endgroup$
    – Nate Eldredge
    Commented Feb 8, 2015 at 16:32

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