# Why do some airports have more than 2 runways, when LHR can get by with 2?

I was looking at aerial imagery of various airports and noticed how some have a large number of runways (4-6), while others have a small number. Specifically, I noticed that Heathrow LHR only has 2 runways, but it is the busiest airport in Europe by passengers. In comparison, the following busiest airport have many more runways (CDG has 4, AMS has 6), but fewer passengers.

Why do some airports have more than 2 runways, when LHR can get by with 2?

• but fewer passengers More passengers != more planes. What if Amsterdam has more cargo traffic than Heathrow? Don't know, but you might want to check the actual plane number serviced. – Stelios Adamantidis Jul 18 '17 at 15:58
• Amsterdam does have 6 runways, but they only ever use 2 or 3 at once for commercial traffic, since you can't just independently use runways that intersect, for example. – J. Hougaard Jul 18 '17 at 16:18
• Heathrow has several more runways, it's called Gatwick, Luton, Stansted, and London City airports... – jwenting Jul 20 '17 at 10:01
• Please do not substantially edit a question to invalidate existing answers. If you need to make such a change, just ask a new question. Thanks. – casey Aug 5 '17 at 2:44
• It is a question related to politics more than aviation – Him Aug 18 '17 at 16:55

Heathrow is somewhat of a standout when it comes to volume. Your wording, that LHR "gets by" with 2 runways is apt. By movements, it is the busiest 2-runway airport in the world. By passenger volume it is second only to Dubai Intl. (Note, though, that DXB is home to Emirates, who has the world's largest fleet of A380's. They are the only airport that averages over 200 passengers per movement!)

Aircraft movement is the best way to look at it from a runway usage standpoint. The following chart is sorted by aircraft movement.*

As you can see, the top 3 all have 5 or more runways. There are 7 large airports with 5 or more rwys and they all fall in the top 16. The top 16 is rounded out by 5 airports with 4 runways, one with 3 runways and... LHR. The next 2-rwy airport on the list is Benito Juarez Intl. in Mexico City clear down at 21st on the list.

Any busy airport with 2 runways has to make those runways work as tightly as possible with little room for error. Otherwise they end up with delays. If I sort the list by movements per rwy, all of those with 2 rwys rise to the top. 10 of the top 15 have 2 rwys.

So, how does LHR pull it off? How do they manage to pack all those flights in to just two runways?There's a downside to handling that kind of volume with so few runways. The following collage gives a clue as to what that is.

Those are just a random pick of arrivals at a couple of random times yesterday morning at LHR. There was no significant weather at the times. As you can see, you just don't arrive at LHR without being put in a holding stack. Every single flight I could find had to do at least one racetrack. At any point during the day, in places like Chesham, Effingham and Brentwood, if you look up there will be as many as 6 or 7 aircraft doing racetracks waiting to be cleared into Heathrow. That makes for very efficient runway usage when there are 20 planes waiting in line, but it's terribly inefficient for the airlines and passengers to have to spend so much time burning fuel circling around London.

On the flip side, building more runways has a down side too. It will get the planes out of the air quicker, but, as happens at Schipol - which has 6 runways - you can end up with a long taxi back to the terminal.

• All data was taken from Wikipedia.
• 'nearly an hour' seems to be an exaggeration, here they mention 20 minutes, and wiki says 15 minutes. – ROIMaison Jul 20 '17 at 8:34
• The long delay isn't caused by the 6 runways, it's caused by the orientation of that 6th runway. If it had been rotated by 20 degrees CCW, the south end would have been a lot closer to the terminal, but the north end would have been near the local golf club. – MSalters Jul 20 '17 at 13:20
• @ROIMaison I've never been there. Just going by what I've heard others say, and they were probably exaggerating. Looks like probably 15-20 min. Edited to remove the hyperbole – TomMcW Jul 20 '17 at 19:08
• @MSalters Looking at the satellite it looks like the 18R flight path runs pretty much over the two nearest golf courses I can see. I see the path over sparsely populated area to the north. But 20° CCW would put the path right over Haarlem. So it's certainly aligned for noise abatement reasons. – TomMcW Jul 20 '17 at 19:15
• 👍 a favorite of mine: youtu.be/kGMVl3y8GxI – ymb1 Jul 21 '17 at 0:37

Don't assume that a higher number of individual runways means a higher possible throughput. The runways at LHR can be used at the same time - this instantly puts them at an advantage. Many older airfields have a typical A shape runway, with 3 intersecting runways - only one runway can ever be used at once in this configuration. Other factors would include noise abatement and licensing restrictions - airports are often controversial, with flights artificially limited by legislation.

Beyond that, it's possible that not all runways are capable of operating with heavy (physically) traffic, may not have the same ILS capabilities and so on.

Finally, just because an airport COULD host more aircraft than LHR doesn't mean it will. LHR is an exceptionally busy hub airport operating at almost maximum capacity all year round. I could build a 20 runway airport in Iceland and wouldn't come close to Heathrows throughput.

• Even two parallel runways can’t necessarily be used independently; e.g., the two main runways at FRA are too close for really independent use, which necessitated the addition of two other runways. – chirlu Jul 19 '17 at 9:45
• These are relevant points, but I don't see this as answering the question. Runways cost money, so why build them if they are not necessary? – Thomas Jul 19 '17 at 21:32
• @Thomas: So that one can be closed if required (accident, maintenance, conditions) and the airport left open? – mins Jul 20 '17 at 7:21
• @Thomas The question was changed since I answered – Dan Jul 20 '17 at 9:13
• @Dan Thanks for the great answer. I did change the question according to a comment, but your answer does bring up important points that I do think contribute to the answer of the new question. Thanks! – PhilippNagel Jul 20 '17 at 13:53

To complement Dan and TomMc:

• Having perpendicular runways like in JFK allow for less cross wind take off / landing
• Having multiple runways with less traffic allow more flexibility if one runway was not usable (tire burst at Gatwick few days ago caused a lot of diverts / delays / cancellation because only one runway was open)
• Some airports expanded and created new longer / larger runways for bigger planes