
Mass Transit Optimization for Buses: The Depot Problem - amoshag
https://www.optibus.com/mass-transit-optimization-for-buses-the-depot-problem/
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honorious
That looks like an interesting problem!

1) What are the metrics that mass transit operators tend to optimize for? Do
you think they are in line with improving the service to customers?

2) How much is "dependability" of a mass transit service a metric that
operators are interested in?

Intuitively I feel that there are places (e.g. Chicago) where I know that I
can get out of the house, get the bus/train, and get to my destination with
little variance in arrival time.

Others (like SF), where the variance on the arrival time seems much higher:
e.g., generally related to unexpected delays while waiting for train/bus.

Do you think it's possible to optimize on such factors?

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CaliforniaKarl
I think you should take a look at the documentation behind VTA's "Next
Network": [https://nextnetwork.vta.org/document-
library](https://nextnetwork.vta.org/document-library)

It is planning that was done to prepare for when BART service reaches Santa
Clara county, and how the bus network will need to be reorganized. In the
documents, you can see how they looked at different plans, covering different
levels of geography vs. population.

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ebikelaw
But why would you look at VTA when it's one of the worst-performing systems in
the nation? Their ridership is in freefall.

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whalesalad
Acknowledging the cookie warning on the site has resulted in an endless 500
loop.

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1stranger
Sorry for being off-topic but I'm still going to use this as an opportunity to
vent. This is the most pointless piece of regulation. It's unfortunate non-US
users are also subjected to it. What bit of good does it really do for your
average user? It's complete overregulation. If users don't want cookies they
can turn them off in their browser. The average user doesn't know or care and
these incessant popups help nobody.

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letcree
> non-US users

It is an EU policy, not US
([http://ec.europa.eu/ipg/basics/legal/cookies/index_en.htm](http://ec.europa.eu/ipg/basics/legal/cookies/index_en.htm)).

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lucasmullens
Right, but US users see the warning too is what the parent post was getting
at.

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blt
This is really cool. Is it possible to express the edge coloring constraints
simply via integer linear programming? This seems like the type of problem
that might be NP-hard but tractable in practice with good heuristics.

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indiesolver
You can use heuristics if/when the problem becomes ugly due to various
constraints you may impose. The trick is to select heuristics depending on the
problem at hand and in a way that their hyperparameter values are selected
properly.

~~~
wenc
Most modern solvers like CPLEX and Gurobi have built-in heuristics [1] that
are automatically selected and applied without user intervention. They
typically exploit the structure of the problem or encode the experiences of
the developers over large problem testsets.

The default heuristics for commercial solvers are actually pretty darned good
these days and there's typically no need to hand-pick them.

In the MIP world, they are the secret sauce to fast solution times.

Hyperparameter tuning has been studied for MIPs (many papers written on this),
but ultimately they are black box solutions. My experience inclines me to not
even consider hyperparameters except as a last resort or unless you know
something specific that a hyperparameter can exploit; there are other more
high leverage things than can be done.

Random perturbations to the problem have been found to be much more fruitful
for forcing a diversity of branch traversal paths and have lead to significant
speedups. (M. Fischetti popularized this idea in 2010s [2])

[1] [https://resources.mpi-
inf.mpg.de/conferences/adfocs-03/Slide...](https://resources.mpi-
inf.mpg.de/conferences/adfocs-03/Slides/Rothberg_3.pdf) Also: [http://transp-
or.epfl.ch/zinal/2017/slides/group5.pdf](http://transp-
or.epfl.ch/zinal/2017/slides/group5.pdf)

[2]
[https://mat.tepper.cmu.edu/blog/index.php/2012/09/25/fischet...](https://mat.tepper.cmu.edu/blog/index.php/2012/09/25/fischetti-
speeds-up-optimization-with-randomness/)

~~~
indiesolver
Thank you for providing useful references. Hyperparameter tuning can
accelarate CPLEX by 10x and more depending on problem instances (however, it
it true that each new version of CPLEX is faster and faster).

What I meant is that in the case if your problem is formulated in a way that
the CPLEX and Gurobi cannot treat it (e.g., stochastic and multiobjective) and
is not very large-scale, then one can use heuristics. However, the efficiency
of the latter will likely depend on hyperparameter settings which need to be
set properly.

~~~
wenc
> What I meant is that in the case if your problem is formulated in a way that
> the CPLEX and Gurobi cannot treat it (e.g., stochastic and multiobjective)
> and is not very large-scale, then one can use heuristics. However, the
> efficiency of the latter will likely depend on hyperparameter settings which
> need to be set properly.

Ah makes sense... stochastic and multiobjective formulations have
superstructures that are not exploited by MIP solvers by default, so
hyperparameter tuning might be useful. Creating (exact) heuristics for these
superstructures are also an active area of research.

Some solvers like CPLEX are starting to natively support higher level
structures like Benders decompositions [1], but they will never support every
structural variation.

[1] Benders:
[https://www.ibm.com/support/knowledgecenter/en/SSSA5P_12.7.0...](https://www.ibm.com/support/knowledgecenter/en/SSSA5P_12.7.0/ilog.odms.cplex.help/CPLEX/ReleaseNotes/topics/releasenotes127/newBenders.html)

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akeck
Also, busses in transit apparently follow "universality".
[https://www.quantamagazine.org/in-mysterious-pattern-math-
an...](https://www.quantamagazine.org/in-mysterious-pattern-math-and-nature-
converge-20130205/)

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andbberger
Oh gosh what a mess of an article... completely undecipherable. There are many
kinds of universality... this article concerns the flavor where many kinds of
physical systems appear to be shockingly well-modeled as random matrices. But
doesn't manage to convey a single kernel of what this __means__, it just plops
information on you like a high-school math class. Tells you the name of things
and some basic properties, leaves you with the misleading impression that you
have come away with some better understanding...

Here's something more substantive to chew on, about universality in
transitions to chaos: [1]. Turns out that many chaotic systems 'descend' into
chaos in the very same way. What does that really _mean_? I have no idea, but
at least this discussion rigorously explains what this universality class is,
instead of dousing you with feel good science-hoodoo-voodoo quotes.

[1]
[http://www.cns.gatech.edu/PHYS-4267/UFO.pdf](http://www.cns.gatech.edu/PHYS-4267/UFO.pdf)

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AstralStorm
The thing you're looking for is called Borel measure. (I think this is what
you mean at least.) It is a part of advanced topology.

Explaining enough topology for a typical reader to get it is a hard task. As
in really hard.

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andbberger
Hmm, I'm not sure what you mean. Can you elaborate?

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mac01021
Anyone else have a ton of trouble understanding the example schedule and how
it's represented as a graph?

I don't know if it's poorly written or if my brain is deteriorating.

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ishaym
Which one? I'd be glad to explain

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ishaym
The edges between the trips mean that one trip can be performed after the
other on the same vehicle. The costs on these edges represent the distance of
the idle trip - if they are far away - it would be more expensive. The depot
pull outs are connected to the earlier trips,and depot pull ins to the later
trips. The cost of these edges also represents the distance of the depot from
this trip.

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chaoxu
It is unclear what is the objective. Minimize deadhead costs? If so, solving
it with min-cost circulation with lower-bound. It would be much cleaner.

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ShaniNat
Amazing! This article was very interesting. Thanks!

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shooltz
Awesome article - super interesting..

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BigDaveTheGiant
Interesting

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adir223
Is this operational already?

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amoshag
Definitely! In cities such as Las Vegas, Washington DC, Austin, and many
others. See optibus.com for more info

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shaiu
interesting and educational article

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dang
All: please don't post promotional comments. We ban accounts that do that.

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rel121
Very interesting!

