
Caltrain Vibration and Volatility Analysis - mmcclure
https://www.nathanblack.me/post/caltrain-vibration-and-volatility-analysis
======
Animats
He's seeing mostly the suspension problems of the older cars, not the track
quality. Caltrain replaced all their track about 15 years ago, going to
concrete ties and welded rail.

Caltrain uses a track geometry car twice a year to measure the rail
geometry.[1] Those also measure vibration. The Shinkansen system in Japan does
that once a week.[2] That's a very good system but extremely high maintenance.
The Shinkansen lines have track maintenance every night.

There's a whole cult thing in Japan around "Dr Yellow", the track inspection
trains. They're special-purpose 7-car Shinkansen trainsets with automated
track inspection gear, and operate at full line speed, so they don't delay
traffic.

[1]
[http://www.caltrain.com/projectsplans/Projects/Caltrain_Capi...](http://www.caltrain.com/projectsplans/Projects/Caltrain_Capital_Program/System_Maintenance/Other_Maintenance.html)

[2]
[https://en.wikipedia.org/wiki/Doctor_Yellow](https://en.wikipedia.org/wiki/Doctor_Yellow)

~~~
Symbiote
Twice a _year_?!

It's not just Japan. France and Britain check their tracks every 2 weeks.

The British high speed measurement train has a site with pictures of some
sensors, statistics ("captures around 10TB of image data every 440 miles") and
a video showing more sensors, and an on-train server room.

[https://www.networkrail.co.uk/running-the-railway/looking-
af...](https://www.networkrail.co.uk/running-the-railway/looking-after-the-
railway/our-fleet-machines-and-vehicles/new-measurement-train-nmt)

~~~
goodcanadian
From your link:

 _-The train surveys 4,800 miles of track every two weeks.

-The train covers 115,000 miles in a year._

It does not cover the entire system every two weeks.

EDIT: Wikipedia suggests a little over 10,000 miles of track in the UK, so it
might be going over it all once a month though I suspect that heavily used
high speed lines are covered more frequently than less used lines (which are
more comparable to Caltrain).

~~~
teh_klev
There are multiple inspection trains, not all of them need to be high speed.
The well known "flying banana" is used to cover high speed lines, but for
lines with lower top speeds there's also a fleet of loco hauled measurement
and inspection trains that cover low speed and branch lines.

~~~
Symbiote
This article says the other trains cover routes monthly.

[https://rail-record.co.uk/guide-to-network-rail-test-trains/](https://rail-
record.co.uk/guide-to-network-rail-test-trains/)

~~~
teh_klev
That's a decent article thanks for posting.

------
statico
I’m glad somebody tried to quantify this. Here’s the rocky ride when taking a
late Caltrain bullet from north to south (somewhere before Palo Alto):
[https://imgur.com/gallery/L3LRcld](https://imgur.com/gallery/L3LRcld)

~~~
Symbiote
That's insane! How fast is it going?

I don't think I kept it, but I now understand why it was requested by my
friend: I took a video of a thick coin (£1 perhaps, 2.8mm thick) balanced in
the train from Malmø to Copenhagen.

I can't remember how long it stayed balanced, at least a couple of minutes,
but something like a full wine glass would be fine for the whole journey.

Edit: here's a video of a coin balanced for over 20 minutes on a Chinese HSR
train:
[https://www.youtube.com/watch?v=fumYdO9XknE](https://www.youtube.com/watch?v=fumYdO9XknE)

~~~
inferiorhuman
Caltrain tops out at 79 mph or about 127 km/h, so most likely 100 km/h or
slower.

------
supernova87a
I had wanted to do an analysis like this too -- had even recorded the trace of
acceleration using iPhone during rides. But the main thing I thought would be
useful would be to overplot the acceleration levels of other train systems in
the US and Europe/Asia for comparison.

Caltrain is simply an embarrassment to ride and realize this is what the
center of global tech has to put up with. I swear a visitor from any other
country with a reasonable rail system would ride Caltrain and think the train
was about to shake itself apart. (Yes I realize the old silver gallery cars
are especially bad while the Bombardier ones are better)

Even if the gross level of shaking were resolved, Caltrain and most other
trains we put up with here are so incredibly loud compared to other more
advanced systems. You go to Germany, and even their subways (subways!) are so
quiet as to feel self-conscious when you're talking on them. And in the
meantime BART -- despite being designed well into the 2nd/3rd generation of US
transit systems -- screeches along due to poor rail maintenance.

~~~
ummonk
Funny, I hate the BART screeches so much that I consider Caltrain great in
comparison. Guess I'm in blissful ignorance of what is possible. Hopefully the
switch to electric trains in a decade will make Caltrain better.

~~~
supernova87a
Well actually, I've been told that the problem of rail noise comes from
improper maintenance of the rail track, not the motive nature of the cars
themselves.

Rail requires periodic grinding to be maintained properly. When you see rail
and wheels riding "flat" on each other, that's actually not how it's supposed
to be -- that kind of maximum contact actually produces the squealing because
the surface area has lots of opportunity to make friction-induced noise.

Supposedly, when you see a rail that's completely shiny on the top surface
from being worn down, that's a sign that it hasn't been properly maintained.

A properly ground rail and wheel actually is only interacting on a very small
edge of contact -- and this is what produces a quiet ride. A properly
maintained rail will be quieter than almost any other mode of transport (noise
from the contact surface). It takes active rail grinding though.

So actually, just a change to electric cars will not maintain quiet operations
(although in the beginning I'm sure the newness of it will help).
BART/Caltrain actually need to conduct the rail maintenance in order to keep
it quiet.

Unfortunately, whether it's due to budget priorities being elsewhere, or an
indiscriminate customer who puts up with this, unless that aspect changes,
we'll be back in the same place. I don't even know whether the conductors --
the ones who would be among the first to notice such issues -- are even
trained to understand this.

I encourage anyone to go ride the high speed rails of Germany, France, Italy,
China, Japan, Korea, to understand what properly maintained rail is capable of
feeling like. Or even the U-bahn in Munich, Frankfurt, too.

~~~
inferiorhuman
_Well actually, I 've been told that the problem of rail noise comes from
improper maintenance of the rail track, not the motive nature of the cars
themselves. _

Noise on BART is due to a liberal application of NIH. BART literally
reinvented the wheel – they used flat profile wheels (nobody else does this)
which dramatically increased noise and wear. BART also spaced the tracks too
tightly in turns further increasing noise and wear. They made their cars out
of aluminum to save weight, creating a bit of an echo chamber (this got worse
once they removed the carpeting). Caltrain doesn't have the luxury of
lightweight rail cars since they share tracks with freight service.

BART doesn't bother greasing the tracks like nearly every other rail system
(almost certainly an artifact of their homebrew train control system).
Unfortunately while reinventing everything they opted against decoupling the
wheels from each other (a.k.a. using a differential like a car or truck
might).

Oh and let's not forget the Oakland Wye, BART's testament to noise, poor
service, and political dysfunction.

Simply put BART can't really grind the rail fast enough to keep everything
quiet for a meaningful period of time (if they could I assume the wear on the
tracks would be astronomical). BART also needs custom rail grinders and
whatnot because hey why not throw a custom track gauge into the mix.

 _So actually, just a change to electric cars will not maintain quiet
operations_

Caltrain is fairly quiet, at least inside. At the very least the
electrification will certainly help with noise while stopped at a station.

 _I encourage anyone to go ride the high speed rails of Germany, France,
Italy, China, Japan, Korea, to understand what properly maintained rail is
capable of feeling like. Or even the U-bahn in Munich, Frankfurt, too._

Spain is missing from your list, they were instrumental in getting the
Pendolino developed and, IIRC, have more high speed track than any other
European country.

~~~
ummonk
_Oh and let 's not forget the Oakland Wye, BART's testament to noise, poor
service, and political dysfunction._

Is that worse than the SFO Wye? Samtrans had to create a bus shuttle from
Millbrae to SFO because the BART service is so useless for traveling between
Caltrain and SFO most times of day.

~~~
inferiorhuman
Sure. SFO is a clusterfuck of BART's own doing, BART's refusal to coordinate
with other transit agencies is infuriating (especially at their much
ballyhooed multimodal station). Oakland, OTOH, is an example of how little
priority the Bay Area places on usable transit. That Wye wouldn't be here but
for the one store owner.

~~~
supernova87a
_but for the one store owner_

What's the story behind that??

~~~
inferiorhuman
I'd have to look it up to get more precise details but essentially back when
BART was being built out originally they wanted to build through developed
land (could've just been the underground rights). They were able to acquire
everything except for one parcel. I'm hazy why eminent domain wasn't used
(especially since it's been so wildly abused elsewhere in the country in the
subsequent decades), but ultimately BART had to build around this property
resulting in an absurdly tight curve. The store is gone but the wye remains as
a bottleneck – BART trains have to slow to walking speed (ok ok about 18 mph)
to go through it.

Edit:

[https://sanfrancisco.cbslocal.com/2019/05/07/brake-
slamming-...](https://sanfrancisco.cbslocal.com/2019/05/07/brake-slamming-
bart-turn-in-oakland-is-the-result-of-an-old-political-favor/)

------
jo-m
Caltrain will soon get modern electrical trains [1] which have been in use for
8 years in Switzerland [2] and which will solve the vibration issues.

[1] [https://calmod.org/electric-trains/](https://calmod.org/electric-trains/)

[2]
[https://en.wikipedia.org/wiki/Stadler_KISS](https://en.wikipedia.org/wiki/Stadler_KISS)

~~~
hcnews
It seems like this isn't going to be a reality for another half-a-decade at
least. (2+ years of constructions and 2+ years of productionization for
consumer traffic).

------
Hansenq
Thanks for doing this analysis!

After riding other transit in the US (NJ Transit, LIRR, Amtrak, BART, misc
Subways), high speed rail in China and Japan, and trains in Europe; Caltrain
stands out to me as the most jerky train I've been on. Often times high speed
rail in East Asian countries are so smooth that you can balance a coin on its
edge without falling. Comparing apples to apples, even NJ Transit and LIRR are
noticeably smoother than Caltrain. It would be interesting to see what the
difference is between systems.

> Looking at data from a few different trips, Caltrain does a good job
> subjecting passengers to no more than 1g of roughness in any direction.

This at first to me seemed like a low bar (relative to other trains out
there), but then I forgot about the sudden jerks and direction changes the SF
Muni and NY Subway often subject passengers. 1g in any direction I suppose is
good for subways, but still poor for trains overall.

Unfortunately I doubt Caltrain's current Electrification project won't solve
any of these issues, given that it seems like more issues with the track, not
with the power source. Perhaps the new trains might help?

~~~
nhf
Much of the side-to-side jerking is a combination of the poor suspension on
the trucks (bogies) of the older Gallery train cars and fast running over
track switches. The Gallery cars are the ones that look like steel toasters.

If you take a ride in one of the "newer" Bombardier cars (the octagonal ones)
the ride is much smoother and the bumps are almost imperceptible with little
swaying. I'd imagine the new trains post-electrification will also be much
better on the suspension front.

~~~
carlob
> I'd imagine the new trains post-electrification will also be much better on
> the suspension front.

So right now this is still Diesel?

~~~
inferiorhuman
Yep. Towns along the peninsula (looking at you Atherton) are fighting
electrification (as well as grade separation) tooth and nail.

~~~
Symbiote
Why? What's the disadvantage for them?

Just the installation cost?

~~~
inferiorhuman
Mostly they don't want to mingle with the hoi polloi.

Atherton (not Belmont – all those shitty little peninsula towns blend together
in my mind) sued because they didn't want trees removed to make way for
overhead wires (the claim was that "cleaner" diesel would be better than
electric)[0]. Then they sued because the poles were going to be 10 ft higher
than promised[1]. Another Atherton resident[2] sued because he wanted Union
Pacific to explicitly approve everything beforehand. More dreck[3].

Caltrain's getting sued left and right over the electrification, starved for
money by BART, and generally ignored by politicians. If you're ever curious
about why Bay Area transit is as bad as it is, Caltrain is a great case study.

0:
[https://en.wikipedia.org/wiki/Electrification_of_Caltrain#La...](https://en.wikipedia.org/wiki/Electrification_of_Caltrain#Lawsuits)

1: [https://www.almanacnews.com/news/2017/12/21/atherton-
battlin...](https://www.almanacnews.com/news/2017/12/21/atherton-battling-
caltrain-over-electrification-poles)

2: [http://www.cahsrblog.com/2009/08/another-peninsula-nimby-
law...](http://www.cahsrblog.com/2009/08/another-peninsula-nimby-lawsuit/)

3: [https://caltrain-hsr.blogspot.com/2009/08/atherton-et-al-
law...](https://caltrain-hsr.blogspot.com/2009/08/atherton-et-al-lawsuit-
decided.html)

~~~
winkeyless
Not hard to see what their real intent was.

When some have the freedom of protecting their private land, others end up
with the freedom of riding diesel only, underfunded trains. The liberty of
some seems greater than others’.

~~~
inferiorhuman
I wonder a bit though as advocating for diesels service seems a bit like
they're shooting themselves in the foot, at least in terms of air quality.

------
Anechoic
Soem comments on both the article, and other comments here:

\- It's an interesting assessment, but without know the details of how he did
the measurement, take care in interpreting the results. If he was using a
smart-phone just lying on s seat of floor, the data are almost certainly
(mostly) meaningless. If he was using a professional triaxial accelerometer
that was rigidly or semi-rigidly attached to the floor, the data are more
representative.

\- With regards to comments about the data being related to track conditions.
Passenger trains have two sets of suspension - the primary suspension between
the axles and trucks (bogies for our European/Asian friends) and the secondary
suspension between the truck and the passenger car. The secondary suspension
is typically very soft for ride-quality purposes and is mostly isolated from
the track. The vertical vibration levels measured here are almost entirely a
result of the ride-quality decisions made by the manufacturer and agency
engineers, and less so about the track condition.

\- As pointed out by nhf and inferiorhuman, the side-to-side jerkiness
(lateral vibfration) is likely related to track condition and is some
combination of track alignment problems and wheel hunting (there the wheels on
the solid axle bounce sideways back-and-forth between the parallel rails).

\- Electrifying the line will have no affect on the cabin vibration unless
Caltrains elects to purchase entirely new passenger cars with different
secondary suspension design goals. If the new electric locomotives are
pulling/pushing the same passenger coaches, the vibration will be the same.

\- From personal experience I can tell you that the TransRapid TR08 (German
system, used in China) can gave similar subjective levels of jerkiness when
the guideway configuration has a sudden change.

~~~
laurencerowe
Caltrain is buying modern EMU stock where traction is distributed across the
passenger cars.

------
hnews_account_1
From the synopsis:

> It's important to use dynamic measures in a dynamic system. I often see the
> mistake of using a static value for mean or kurtosis, unaware of how it
> changes over time.

This is both important to note, and unavoidable. You can account for changes
in volatility in pure data analysis, but when developing mathematical models
of time series, data stationarity _has_ to be assumed for closed form
solutions. Even if the volatility itself followed its own model (say garch
could model it accurately), it can be iteratively reduced to a stationary
series (I'm not sure if there's proof of this, but that's how most time series
courses teach it - take first diff, second diff, log etc).

Markets are a similar level of complexity, but to compare anything to a
reflexive system such as a market is kinda skirting the main issue of markets
- reflexivity. You cannot find a closed form solution for it using current
mathematics. Finance developed a distribution based mathematics called
stochastic calculus (used in other fields, but it's the backbone of finance)
to deal with this, but even there, the assumptions are highly restrictive
compared to real world conditions.

------
brian-armstrong
This article is somewhat interesting but it appears to be a not so subtle
advertisement for a trading platform.

~~~
mmcclure
Really curious where you're getting that impression.

> I like rhythm and vibration and I trade financial market volatility at
> sha.capital.

This is the only mention of anything associated with his work, and it's not
even hyperlinked. It's a fund at that, not a platform, and he doesn't even
make an attempt at any kind of solicitation in the post. If this is an attempt
at advertising it's a pretty poor one.

------
CaliforniaKarl
What would be interesting next would be to see what the track geometry is like
in the area of & around the worst events.

Something like what you’d get from this:
[https://youtu.be/Ite0l4uJ_fM?t=3m55s](https://youtu.be/Ite0l4uJ_fM?t=3m55s)

------
blululu
This is fun. Interesting analysis. A few quick thoughts:

Why the focus on Jerk/Volatility instead of Acceleration/Force? The energy
imparted to the passengers is proportional to the forces. Is there any reason
to suppose that Jerk is more important to the experience of discomfort (or
mechanical wear for that matter)?

The analysis notes that the distribution is not normal, but it does not
explore the what the underlying distribution might be instead. Given that the
train's velocity is constantly accelerating/decelerating it seems unlikely
that it would be a single distribution. However it may be the case that the
observed variations are the result of a superposition of normal distributions.
A Fourier transform could maybe helpful to explore these aspects.

~~~
nomel
Acceleration/Force is easily compensated for, if its constant. For example,
taking a turn or coming to a gradual stop is completely comfortable. Only the
change is uncomfortable.

------
m_eiman
I've played with the thought of doing something like this to create a tool for
assisting (and perhaps evaluating) drivers of buses:

* make a device that logs acceleration in various directions and performs suitable statistical analysis in real time. * combine it with passenger evaluations of ride behavior (tell users to press a button when the ride is uncomfortable) to train a neural net to evaluate ride smoothness * install devices in all buses, with a display placed in front of the driver that shows current ride comfort and warns if things get too problematic

------
0xFFFE
Just something I noticed [there is a plate near the doors], cars were built in
1984 and refurbished by Alstom few years ago.

------
smaslennikov
I'm interested in the controls for this analysis, which I didn't notice in the
article. Might've missed them.

I'm mainly talking about how the device was mounted - because if it's simply
kept on person, a lot of this vibration is muffled, right?

------
rabryan35
Fun read - great article for getting a better intuition on real world data
analysis of dynamic systems (especially the part showing how bad conflating
mean and median is).

Only gripe is it’s not an interactive notebook of some sort so others could
play with the data.

------
cameldrv
The deviation from a normal distribution is really interesting!

