
The FedEx Problem - subnaught
http://arxiv.org/abs/1410.6723
======
graycat
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
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
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.

~~~
ars
How does the pilot know the weight? Do they weight each piece of luggage
individually, or are there sensors in the wheels?

~~~
teraflop
Good question! Here's some information from aviation.stackexchange:
[http://aviation.stackexchange.com/questions/9975/do-
addition...](http://aviation.stackexchange.com/questions/9975/do-additional-
passengers-impact-on-weight-and-balance-of-a-domestic-airliner)

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.

~~~
WalterBright
I wonder if gluing strain gauges to the landing gear struts would be accurate
enough once calibrated.

There has been at least one crash due to mis-estimating the weight of the
passengers + luggage + cargo. A strain gauge on the struts, even if
inaccurate, could provide a backup sanity check for the weights.

~~~
graycat
As I joined FedEx, I was told that they had already worked out sensors, of
some kind (I never saw details), on the landing gear that would give the data
needed for knowing and controlling _weight and balance_. For _balance_ ,
right, e.g., don't want all the weight near the tail and, instead, want the
weight more evenly distributed in the cargo area along the length of the
plane, that is, want the load in _balance_.

So, yes, FedEx did think of having sensors, of some kind, in the landing gear.

But I never heard more about such sensors, and, for the times I rode the jump
seat in the planes, I never saw pilots working with weight and balance from
data from the landing gear.

Maybe later, after I went to grad school, FedEx did do something with such
sensors.

So, right, the sensors are a good idea and were considered and, maybe,
eventually implemented.

------
iandanforth
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."

------
ISL
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
Woah, Louisville is much closer. Loiusville may be the closest city to Point H
that has an airport.

~~~
tg3
I believe Indianapolis is closer to H than Louisville (but probably not by
much).

------
mcginleyr1
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)

------
larrys
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..

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pain_perdu
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=77323599...](https://www.fedex.com/apps/fedextrack/?tracknumbers=773235995640&language=en&cntry_code=ca)

~~~
jonah
And when you order things direct from China, they usually come through Alaska.

~~~
1fatboy
Used to - the one I got yesterday came to Memphis directly from H.K.

------
1fatboy
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.

------
ableal
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
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
Oops. Scanned too quickly on the way to the conclusions. Thanks for the heads
up.

(Drats, it was a nice one.)

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

~~~
wilsynet
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
There are already sorting facilities everywhere though.

------
SFjulie1
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)

