Why don’t most major airports have 6-8 parallel runways instead of 2-4 (sometimes intersecting) runways?
Seems like you could land and takeoff airplanes much more easily and handily with 6-8 runways instead of 2-4 runways, and with no possibility of collision on intersecting runways. And it would be much easier to clear out an available runway in the event of an emergency.
If all the runways are parallel, then an airport with 6 runways wouldn’t have to be significantly larger than one with 4 runways.
Couple of reasons:
Runways are expensive - so an airport tends to have enough for expected traffic, but not an excess.
Wind doesn’t always blow from one direction - so runways at different orientations may be needed.
Flying an airplane isn’t like driving a car, where you have physical streets and lanes. (There are virtual ‘radio’ lanes.) Airports have ‘traffic patterns’. These consist of an upwind leg (aligned with the runway, flying into the wind at the departure end), a crosswind leg (90º from the upwind leg), a downwind leg (flying downwind parallel to the runway), a base leg (perpendicular to the runway at the approach end), and a final leg (lined up with the runway, flying into the wind, at the approach end). Think of them as big, rectangular loops. With two runways you can have right-traffic and left-traffic patterns so that the aircraft remain separated. (I’ve never piloted an airplane into an airport that had three parallel runways.) If you have six parallel runways, you’re going to have to have traffic patterns somewhere. I suppose you could stack them, one difference between flying and driving being that you have a third dimension, but it might be a little dicy when (‘when’, not ‘if’) planes are not at the correct altitude for the pattern. So one reason for not having 6 to 8 parallel runways is safety.
Another factor is cost. Runways are enormously expensive. No; more expensive than that. And so is the land on which to put them.
Intersecting runways are used for varying wind conditions. Airplanes like to land as nearly into the wind as possible, as this gives them a slower ground speed for a given airspeed. Slower ground speed means they need less runway to take off or land. Runways are built so that they are favoured by the prevailing winds. When winds generally come from a couple of directions, intersecting runways are useful.
It’s mostly a one-time expense, though, right? And runways could last for many decades. Seems like in the long run (no pun intended,) an extra runway’s benefits would outweigh the drawbacks.
It’d be nigh impossible to monitor that many runways and the air traffic resulting. It’s not just a matter of space, but of coordinating landings and take-offs so the area around the airport isn’t littered with corpses and debris from collisions.
Airports are located near places where people live. If they’re not, they’re rarely used or they immediately get surrounded by homes. That means that they have to be reasonably quiet and they can’t take up acreage the size of Chicago. Those factors mitigate having so many parallel runways. Also, there are clearance issues. Commercial planes don’t fly in formation and would never be cleared to land simultaneously on parallel runways anyway, so six runways aren’t necessary when one will do.
Last, the reason runways intersect is so that planes can land with the wind. Taking off and landing in heavy crosswinds is frowned upon and should be avoided if at all possible. Any conflict between the two runways should be taken care of by ground control.
It seems your idea is intended to mitigate congestion and delays. Well, those would still exist. The delays are rarely the fault of the airport, they are usually because the airlines establish unreasonable schedules and try to force a million planes into a window suitable for two.
Runway maintenance is not and can run hundreds of thousands, if not millions, a year.
Also extra air traffic control is not cheap.
Yeah, that was what I had in mind. I see the problem now.
Eh? Guess you haven’t been to Dallas-Ft. Worth? Or Chicago O’Hare? Or DIA? Or…
Also, even with a bunch of parallel runways, you still have to navigate traffic on the ground. An airplane landing way out on Runway #18 will need to cross over Runways 2 thru 17 to get to the gate, which means you can’t land on those runways while it’s taxiing.
Also also, one of the biggest factors in airport delays is bad weather. When the fog rolls in, those 16 extra runways aren’t gonna help out one bit.
And, if you build too many of them, you make a giant swastika, which might send the wrong message to visitors.
You evil bastard. What if Cartooniverse clicks that link and gets all squinked out? Are you going to foot the bill for the therapy sessions?
I didn’t think so. Honestly, if we just took a moment to consider other posters’ sensibilities, this MB would be a much nicer place.
Newer airports do tend to have more parallel runways than crossing. When older airports like LaGuardia were built, they had crossing runways to help with crosswinds. But with vastly more air traffic now, that’s a liability because you can’t use the runways simultaneously (with some exceptions - read on). LaGuardia is a big problem now for this reason.
I remember some sort of public meeting with the LaGuardia manager. He was asked what could be done to alleviate the traffic problems there, and he basically said you’d have to nuke it and start over. Crossing runways were the limiting factor. Nowadays they build mostly parallel, and the crosswinds are the pilots’ problem.
I fly into Boston Logan every day, and there it’s a combination of parallel and crossing runways. We get a lot of LAHSO clearances - Land and Hold Short. This enables some simultaneous use of the crossing runways.
We talked about minimum separation between parallel runways not too long ago, in this thread. It was noted there that runways can only be treated independently (absent extra ground controllers and fancy radar installations) if the runways are over 4300 feet apart. If you had six parallel runways, you would need a little over 4 miles between the outermost two to satisfy this constraint. You can see how land requirements could rapidly make this plan unfeasible.
(Though if they ever build that ridiculous airport in Peotone, it wouldn’t be an issue there)
[Morbo]
RUNWAYS DO NOT WORK THAT WAY! GOODNIGHT!
Runway numbers are actually the compass heading of the runway divided by 10. So a hypothetical Runway 18 would be oriented due south (180 degrees.) If you approach the same runway from the opposite direction, it would be Runway 36.
If you have two parallel runways, they would be 18L and 18R, which from the other direction would be 36R and 36L, respectively. (Right and left get switched.) If you have three parallel runways, you can use L, C, and R.
More than that, and you fake it by using adjacent numbers even though they’re all parallel. For example, DFW famously has 17C, 17R, 18L, and 18R. (Why not 17L instead of 17C? Who knows?)
(ETA: Looking at the map, it’s because they do have a 17L, but it’s way up in the boonies and only 8500 feet long.)
Anyway, airports with more than three parallel runways are rare. Runways take up a great deal of space and are expensive to build and maintain and organizing traffic patterns to use lots of parallel runways simultaneously is tricky and can be dangerous.
Geez, get a grip! He’s clearly talking about the runway numbers as though they are all lines up a parallel. Talking to an average person, calling them runways 1-17 makes a lot more sense than calling them runways 18C, 18LC, 18RC, 18RRC, 18LLC, 18RCR, etc.
The point is still valid: crossing a dozen active runways would be a mess.
Just more evidence that we need to invent flying cars already.
Why, so that we can kill people by the numbers in aviation accidents?
I’ve never seen that. What I’ve seen is 16R, 16L and 15 (even though 15 really has a heading of 160)
If the terminals were located in the center - say, between Runways 9 and 10 - then it would only need to taxi over Runways 17 through 10.
But yes, I get your point.
Why are runways so expensive to build and maintain?
Miles and miles of concrete motorways (freeways) are built every year. How is a runway so much different from this?