22 ms·

The FedEx Problem

229 points by subnaught 12y ago

ISL 12y ago
In Figure 5, you'll note that the UPS Louisville hub is closer to the author's optimal "Point H" than the FedEx hub in Memphis.
- hawkice 12y ago
  Woah, Louisville is much closer. Loiusville may be the closest city to Point H that has an airport.
  - tg3 12y ago
    I believe Indianapolis is closer to H than Louisville (but probably not by much).
graycat 12y ago
Yes, at FedEx, we considered that problem for about three seconds before we noticed that we also needed: (1) A suitable, existing airport at the hub location. (2) Good weather at the hub location, e.g., relatively little snow, fog, or rain. (3) Access to good ramp space, that is, where to park and service the airplanes and sort the packages. (4) Good labor supply, e.g., for the sort center. (5) Relatively low cost of living to keep down prices. (6) Friendly regulatory environment. (7) Candidate airport not too busy, e.g., don't want arriving planes to have to circle a long time before being able to land. (8) Airport with relatively little in cross winds and with more than one runway to pick from in case of winds. (9) Runway altitude not too high, e.g., not high enough to restrict maximum total gross take off weight, e.g., rule out Denver. (10) No tall obstacles, e.g., mountains, near the ends of the runways. (11) Good supplies of jet fuel. (12) Good access to roads for 18 wheel trucks for exchange of packages between trucks and planes, e.g., so that some parts could be trucked to the hub and stored there and shipped directly via the planes to customers that place orders, say, as late as 11 PM for delivery before 10 AM. So, there were about three candidate locations, Memphis and, as I recall, Cincinnati and Kansas City. The Memphis airport had some old WWII hangers next to the runway that FedEx could use for the sort center, aircraft maintenance, and HQ office space. Deal done -- it was Memphis. That's how the decision was really made. Uh, I was there at the time, wrote the first software for scheduling the fleet, had my office next to that of founder, COB, CEO F. Smith.
- cheeseprocedure 12y ago
  I had never considered altitude as a factor in takeoff weight limits. How much load would a typical FedEx flight need to shed to operate out of Denver?
  - WalterBright 12y ago
    I did after once flying out of Denver, and the luggage had to be removed because the airplane was overweight for the altitude and air temperature. Next time you're flying out of Denver, notice how long the takeoff roll is. When my father flew jets out of Denver, he'd hang the tailpipe over the back edge of the runway so he'd have every last foot of runway to get airborne.
    - saryant 12y ago
      The difference in Denver is so significant that United actually swapped all the Houston-based 737s that came over from Continental in the merger with the Denver-based A320s from United. The 737 base moved to Denver and the A320 base moved to Houston. The 737 has better performance with high-altitude takeoffs.
    - ars 12y ago
      How does the pilot know the weight? Do they weight each piece of luggage individually, or are there sensors in the wheels?
      - teraflop 12y ago
        Good question! Here's some information from aviation.stackexchange: http://aviation.stackexchange.com/questions/9975/do-additional-passengers-impact-on-weight-and-balance-of-a-domestic-airliner http://aviation.stackexchange.com/questions/9975/do-addition... Checked luggage is weighed when you drop it off, so presumably the exact weights are available to the pilots. For passengers themselves and their carry-on baggage, accurate weights aren't available so statistical averages are used, based on the number of passengers and their baggage allowances. Airliners do have "squat sensors" in the landing gear, but they're not capable of accurately measuring the aircraft's weight. They're just binary-valued sensors that check whether the gear struts are under stress, to prevent the gear from accidentally being raised while the plane is on the ground.
larrys 12y ago
Weather and other logistical issues (cost of labor) played large part in where Fedex located their hub. It's not simply something that you can solve by mathematics alone. [1] Ditto for Walt Disney World in Florida as another example where in addition to weather and population proximity there was also the cost of land..
mcginleyr1 12y ago
I actually was at an advanced planning and scheduling company and did a POS for station planning. The timings they have things down to are impressive. What's not is the insane excel books I had to read and all the equations I had to lay out that went across the network drive. It was quite a bit of work. But I was able to write an optimizer for it using Gecode (gecode.org)
sjtrny 12y ago
What is the point of a central hub anyway? It doesn't make much sense unless you are sending the package across the country.
- samatman 12y ago
  It's an interface. It turns many tasks (get package a to package b) into two tasks: get all the packages to the hub, and get all the packages out of the hub.
- wilsynet 12y ago
  It's hard to keep the planes full if you don't do a variation on hub and spoke. It is also expensive to have sorting facilities everywhere. Could you theoretically be more efficient? Sure. But it's much harder to buy planes, plan new flights, build a new sorting facility and train staff vs you just running your simulation again on the command line with different parameters.
  - sjtrny 12y ago
    There are already sorting facilities everywhere though.
SFjulie1 12y ago
This is ridiculously easy to solve if you accept: - local optimum that are only 80% better (the choice may not be absolutely optimal and can locally be suptobptimal); - shit will happens and planning have to be redone for each incidents; - an infinite knowledge requiring infinite resource is impossible to achieve thus you have to reason with agent with incomplete global informations others than "thermodynamics global metrics" - you still have to prove you do better than random, - your improvements are costing less than the saving you will do; - this results in a strongly distributed system that is adapatative. All of this can be donne my having simulation with adequate utilities for the agent in the way of this simulation: https://github.com/jul/KISSMyAgent/wiki https://github.com/jul/KISSMyAgent/wiki
iandanforth 12y ago
Buried lead from the article: "We found the minimum to be (39◦, 87◦), a location in Greene County, Indiana, about 70 miles southwest of Indianapolis. From this point the average distance to any person in the country is 795 miles, while the average distance to Memphis is 843 miles. It is interesting to note that as FedEx has grown it has established some secondary hubs, one of them being in Indianapolis. Furthermore, the optimal location is only about 85 miles northwest of Louisville where UPS has established its main hub."
pain_perdu 12y ago
Thanks so much for posting this! I just sent a package from Toronto to New York (a short direct flight) so was curious why it was showing Memphis as the current location. Perfect timing. In case anyone is curious: https://www.fedex.com/apps/fedextrack/?tracknumbers=773235995640&language=en&cntry_code=ca https://www.fedex.com/apps/fedextrack/?tracknumbers=77323599...
- jonah 12y ago
  And when you order things direct from China, they usually come through Alaska.
  - mikeash 12y ago
    Alaska is mostly in between China and North America, though.
  - 1fatboy 12y ago
    Used to - the one I got yesterday came to Memphis directly from H.K.
1fatboy 12y ago
I understand the shortsightedness of Little Rock officials had more to do with FEDEX locating in Memphis than airport inadequacies. Those officials are heir to the geniuses who allowed the University to be stolen away to the far northwest corner of the state.
deleted 12y ago
[deleted]
ableal 12y ago
I sort of collect amusing typos. Right near the top of page 6, label for Figure 2: "FredEx". Might be a Freudian slip - perhaps a FreudEx - or simply the now prevalent autocorrect. (I have "rear window defrogger" and "string loaded door" for trade, lightly used.)
- areyousure 12y ago
  Fyi: that's not a typo. See the middle of page 2, where the author introduces "the FredEx problem". The caption for figure 1 on page 3 also references the same problem.
  - ableal 12y ago
    Oops. Scanned too quickly on the way to the conclusions. Thanks for the heads up. (Drats, it was a nice one.)

229 points by subnaught 12y ago

ISL 12y ago

In Figure 5, you'll note that the UPS Louisville hub is closer to the author's optimal "Point H" than the FedEx hub in Memphis.

hawkice 12y ago
Woah, Louisville is much closer. Loiusville may be the closest city to Point H that has an airport.
- tg3 12y ago
  I believe Indianapolis is closer to H than Louisville (but probably not by much).

graycat 12y ago

Yes, at FedEx, we considered that problem for about three seconds before we noticed that we also needed: (1) A suitable, existing airport at the hub location. (2) Good weather at the hub location, e.g., relatively little snow, fog, or rain. (3) Access to good ramp space, that is, where to park and service the airplanes and sort the packages. (4) Good labor supply, e.g., for the sort center. (5) Relatively low cost of living to keep down prices. (6) Friendly regulatory environment. (7) Candidate airport not too busy, e.g., don't want arriving planes to have to circle a long time before being able to land. (8) Airport with relatively little in cross winds and with more than one runway to pick from in case of winds. (9) Runway altitude not too high, e.g., not high enough to restrict maximum total gross take off weight, e.g., rule out Denver. (10) No tall obstacles, e.g., mountains, near the ends of the runways. (11) Good supplies of jet fuel. (12) Good access to roads for 18 wheel trucks for exchange of packages between trucks and planes, e.g., so that some parts could be trucked to the hub and stored there and shipped directly via the planes to customers that place orders, say, as late as 11 PM for delivery before 10 AM. So, there were about three candidate locations, Memphis and, as I recall, Cincinnati and Kansas City. The Memphis airport had some old WWII hangers next to the runway that FedEx could use for the sort center, aircraft maintenance, and HQ office space. Deal done -- it was Memphis. That's how the decision was really made. Uh, I was there at the time, wrote the first software for scheduling the fleet, had my office next to that of founder, COB, CEO F. Smith.

cheeseprocedure 12y ago
I had never considered altitude as a factor in takeoff weight limits. How much load would a typical FedEx flight need to shed to operate out of Denver?
- WalterBright 12y ago
  I did after once flying out of Denver, and the luggage had to be removed because the airplane was overweight for the altitude and air temperature. Next time you're flying out of Denver, notice how long the takeoff roll is. When my father flew jets out of Denver, he'd hang the tailpipe over the back edge of the runway so he'd have every last foot of runway to get airborne.
  - saryant 12y ago
    The difference in Denver is so significant that United actually swapped all the Houston-based 737s that came over from Continental in the merger with the Denver-based A320s from United. The 737 base moved to Denver and the A320 base moved to Houston. The 737 has better performance with high-altitude takeoffs.
  - ars 12y ago
    How does the pilot know the weight? Do they weight each piece of luggage individually, or are there sensors in the wheels?
    - teraflop 12y ago
      Good question! Here's some information from aviation.stackexchange: http://aviation.stackexchange.com/questions/9975/do-additional-passengers-impact-on-weight-and-balance-of-a-domestic-airliner http://aviation.stackexchange.com/questions/9975/do-addition... Checked luggage is weighed when you drop it off, so presumably the exact weights are available to the pilots. For passengers themselves and their carry-on baggage, accurate weights aren't available so statistical averages are used, based on the number of passengers and their baggage allowances. Airliners do have "squat sensors" in the landing gear, but they're not capable of accurately measuring the aircraft's weight. They're just binary-valued sensors that check whether the gear struts are under stress, to prevent the gear from accidentally being raised while the plane is on the ground.

larrys 12y ago

Weather and other logistical issues (cost of labor) played large part in where Fedex located their hub. It's not simply something that you can solve by mathematics alone. [1] Ditto for Walt Disney World in Florida as another example where in addition to weather and population proximity there was also the cost of land..

mcginleyr1 12y ago

I actually was at an advanced planning and scheduling company and did a POS for station planning. The timings they have things down to are impressive. What's not is the insane excel books I had to read and all the equations I had to lay out that went across the network drive. It was quite a bit of work. But I was able to write an optimizer for it using Gecode (gecode.org)

sjtrny 12y ago

What is the point of a central hub anyway? It doesn't make much sense unless you are sending the package across the country.

samatman 12y ago
It's an interface. It turns many tasks (get package a to package b) into two tasks: get all the packages to the hub, and get all the packages out of the hub.
wilsynet 12y ago
It's hard to keep the planes full if you don't do a variation on hub and spoke. It is also expensive to have sorting facilities everywhere. Could you theoretically be more efficient? Sure. But it's much harder to buy planes, plan new flights, build a new sorting facility and train staff vs you just running your simulation again on the command line with different parameters.
- sjtrny 12y ago
  There are already sorting facilities everywhere though.

SFjulie1 12y ago

This is ridiculously easy to solve if you accept: - local optimum that are only 80% better (the choice may not be absolutely optimal and can locally be suptobptimal); - shit will happens and planning have to be redone for each incidents; - an infinite knowledge requiring infinite resource is impossible to achieve thus you have to reason with agent with incomplete global informations others than "thermodynamics global metrics" - you still have to prove you do better than random, - your improvements are costing less than the saving you will do; - this results in a strongly distributed system that is adapatative. All of this can be donne my having simulation with adequate utilities for the agent in the way of this simulation: https://github.com/jul/KISSMyAgent/wiki https://github.com/jul/KISSMyAgent/wiki

iandanforth 12y ago

Buried lead from the article: "We found the minimum to be (39◦, 87◦), a location in Greene County, Indiana, about 70 miles southwest of Indianapolis. From this point the average distance to any person in the country is 795 miles, while the average distance to Memphis is 843 miles. It is interesting to note that as FedEx has grown it has established some secondary hubs, one of them being in Indianapolis. Furthermore, the optimal location is only about 85 miles northwest of Louisville where UPS has established its main hub."

pain_perdu 12y ago

Thanks so much for posting this! I just sent a package from Toronto to New York (a short direct flight) so was curious why it was showing Memphis as the current location. Perfect timing. In case anyone is curious: https://www.fedex.com/apps/fedextrack/?tracknumbers=773235995640&language=en&cntry_code=ca https://www.fedex.com/apps/fedextrack/?tracknumbers=77323599...

jonah 12y ago
And when you order things direct from China, they usually come through Alaska.
- mikeash 12y ago
  Alaska is mostly in between China and North America, though.
- 1fatboy 12y ago
  Used to - the one I got yesterday came to Memphis directly from H.K.

1fatboy 12y ago

I understand the shortsightedness of Little Rock officials had more to do with FEDEX locating in Memphis than airport inadequacies. Those officials are heir to the geniuses who allowed the University to be stolen away to the far northwest corner of the state.

deleted 12y ago

[deleted]

ableal 12y ago

I sort of collect amusing typos. Right near the top of page 6, label for Figure 2: "FredEx". Might be a Freudian slip - perhaps a FreudEx - or simply the now prevalent autocorrect. (I have "rear window defrogger" and "string loaded door" for trade, lightly used.)

areyousure 12y ago
Fyi: that's not a typo. See the middle of page 2, where the author introduces "the FredEx problem". The caption for figure 1 on page 3 also references the same problem.
- ableal 12y ago
  Oops. Scanned too quickly on the way to the conclusions. Thanks for the heads up. (Drats, it was a nice one.)