Sunset limited top speed

[John Santos]

The error in a wheel-rotation based speedometer as the wheel wears out is proportional to the change in diameter.  Going from a 15" to a 16" car tire is a 16/15 is a 6.7% increase in diameter, so the speed displayed by the speedometer will be 6.7% low.  At 65 mph, it will display about 61 mph, or if it displays 65 mph, you would actually be traveling at 69 mph, maybe enough to get a ticket.

According to Wikipedia, a P42's wheels are 40" in diameter (which I think is typical for a diesel locomotive).  In order for the speedometer to be off by 1%, the diameter would have to be off by 1%, or almost half an inch, which I think would be a HUGE amount of wear on a steel wheel.  I would expect a badly worn wheel would be off by only a few hundreds of an inch.  After truing a wheel, the speedometer might be slightly off, but I don't think this is a big issue.

 

[Asher]

GPS are pretty accurate most times. If you have a stop watch measuring between Mike markers is easy, just check seconds between markers and divide into 3600 = MPH  The numbers don't lie!

 

[caravanman]

No one has mentioned Continental Drift? I believe that continents change size a little due to tectonic plates moving, which may impact speed measurements between mile posts?

Ed.

 

[Bob Dylan]

No one has mentioned Continental Drift? I believe that continents change size a little due to tectonic plates moving, which may impact speed measurements between mile posts?

Ed.

Surely you dont want to confuse us with Scientific Facts?

What about Alternate Facts?? <_<

 

[caravanman]

Surely you dont want to confuse us with Scientific Facts?

What about Alternate Facts?? <_<

You guys can have your own opinions, you can't have your own facts...  

 

[PRR 60]

I was under the impression that modern locomotives use doppler sensors for speed measurement, not wheel rotation measurement. A doppler device is not dependent on wheel circumference thus does not need adjustment to account for wheel wear.

 

[me_little_me]

They need to run at 81 mph to overcome the hours they spend on sidings waiting for freights to go by. I know. We sat for a couple of hours in total on the sunset between NOL and ELP in both directions last year.The 81 raises their numbers from 4 hours late to 3 hours and 59 minutes.

 

[Thirdrail7]

.  After truing a wheel, the speedometer might be slightly off, but I don't think this is a big issue.

And you would be wrong, particularly with issues like wheel slip, speed sensors, cab signals, gps. "Slightly off" can lead to penalties, wheel slide (particularly), wheel slip and that is assuming the wheel was only "slightly off." I wasn't going to bring it up but this train is perfect example of what happens if you if the wheel diameter is off. The fisr system impacted N of WAS was ACSES, the speed control, which impacted the cab signals. Each system was eventually cut out, effectively limiting the speed as PRR60 mentioned and necessitating an en route engine change...and after I suspected after the ACSES failure (a true ACSES failure doesn't occur that often), the wheels were just trued.

So, it can be an issue.

Even so, don't underestimate a 2-3 mph on a long trip.  A cumulative 3mph under speed  over the stretch of the run be the difference between being making your slot or missing your slot. Imagine running 3 mph under on a train like the Meteor. 

 

[chakk]

Let’s not forget global warming, which increases sea level and thus the diameter of the earth. So, under the Law of Conservation of Angular Momentum, the rotational speed of the Earth is declining (like a spinning figure skater extending her arms), giving AUers more time each day to debate this topic about locomotive speed display accuracies.

 

[cpotisch]

But the intent of the question are the tracks displayed as in the above pic ?

Still not totally sure what you're asking. I doubt Waze figured out that he was on a train and concluded that he must be on those tracks. Just happened to be pretty accurate location-wise at that time.

 

[jis]

You guys can have your own opinions, you can't have your own facts...  

Which raises the epistemological question "How does one know that something that is claimed to be a fact by someone is in fact a universal fact"? :lol:

But I think it is true proposition that Continental Drift or a general discussion of Epistemology has not much to do with Sunset Limited or its top speed :unsure:

 

[cpotisch]

Let’s not forget global warming, which increases sea level and thus the diameter of the earth. So, under the Law of Conservation of Angular Momentum, the rotational speed of the Earth is declining (like a spinning figure skater extending her arms), giving AUers more time each day to debate this topic about locomotive speed display accuracies.

Rising sea levels do not increase the diameter of the earth, and we don't feel the earth's rotation. So your point is...?

 

[caravanman]

Which raises the epistemological question "How does one know that something that is claimed to be a fact by someone is in fact a universal fact"? :lol:

But I think it is true proposition that Continental Drift or a general discussion of Epistemology has not much to do with Sunset Limited or its top speed :unsure:

Well, I didn't see why only certain members should have the monopoly on pedantry and obsessive nit picking, so thought I would throw in a random tectonic red herring.

As for "facts", if a certain president states something, one can be sure the opposite is a fact, and that is all the main facts one needs to know... 

 

[jis]

Well, I didn't see why only certain members should have the monopoly on pedantry and obsessive nit picking, so thought I would throw in a random tectonic red herring.

As for "facts", if a certain president states something, one can be sure the opposite is a fact, and that is all the main facts one needs to know... 

And I thought it would be kind of fun to pull your leg and while at it provide a hook for those who might want to learn a bit more about facts or propositions and truth and such

 

[Acela150]

The 79 mph and 59 mph FRA limits are based on the signal system, not track class. In dark territory, trains are limited to 59 mph or track class speed, whichever is lower. Where there is a signal system but no cab signals, auto-stop or other system to stop a train automatically, trains are limited to 79 mph or track class, whichever is lower. Parts of the old Santa Fe have that type of signaling, so Amtrak can operate up to 90 mph in those areas.

Bill, you're dead on. I honestly forgot all about that. I can tell you from my experience that a passenger train running opposing is limited to 59mph or the MAS and Freight in the NS Rule book is 49 or MAS. I also believe that in the new 12th Edition of NORAC trains running on Rule 563 (Cab signals not functioning) are limited to 59mph as well. Previously it was 79mph.  

 

[john h]

So question on the Waze did it lock on the the track presentation ?

I have used Waze for a good number of years and sometimes it kinda drifts, that is most likely caused by temporary losing its triangulation with the constellation .

Yes it locked on the tracks after all railroad workers trucks ride the rails too

 

[John Santos]

And you would be wrong, particularly with issues like wheel slip, speed sensors, cab signals, gps. "Slightly off" can lead to penalties, wheel slide (particularly), wheel slip and that is assuming the wheel was only "slightly off." I wasn't going to bring it up but this train is perfect example of what happens if you if the wheel diameter is off. The fisr system impacted N of WAS was ACSES, the speed control, which impacted the cab signals. Each system was eventually cut out, effectively limiting the speed as PRR60 mentioned and necessitating an en route engine change...and after I suspected after the ACSES failure (a true ACSES failure doesn't occur that often), the wheels were just trued.

So, it can be an issue.

Even so, don't underestimate a 2-3 mph on a long trip.  A cumulative 3mph under speed  over the stretch of the run be the difference between being making your slot or missing your slot. Imagine running 3 mph under on a train like the Meteor. 

2-3 mph  is 1% error if the train is traveling at 2-300 mph, which strikes me as unlikely on any Amtrak route.  At 80 mph, a 2 mph error due to a diameter error would require the diameter be off by 2.5% or 1 inch on a 40" wheel.  Are you claiming that wheel truing removes that much metal?

 

[Thirdrail7]

2-3 mph  is 1% error if the train is traveling at 2-300 mph, which strikes me as unlikely on any Amtrak route.  At 80 mph, a 2 mph error due to a diameter error would require the diameter be off by 2.5% or 1 inch on a 40" wheel.  Are you claiming that wheel truing removes that much metal?

I don't true the wheels myself so I'm not making a claim on how much metal on the wheels is removed. As such,  it may be possible they remove that much metal. There is such things as tread build up that may account for why there may be additional tread which is why the Siemens' engines come with tread scrubbers.  Secondly, I have been ON equipment (including two high speed test trains)  with improper wheel diameter which has caused numerous errors and even required new tests since the speed was 4mph off at speeds above 95mph.  After taking measurements, the Bombardier technician went to the engine, (which had just come out of the shop with nice trued wheels) and reentered the wheel diameter. Once she did that, the speedometer was accurate, allowing the tests to continue.

As such, I am claiming with certainty (particularly with the trains listed above) that saying the speedometer being off after truing the wheels it is not a big deal, can be false.

Rising sea levels do not increase the diameter of the earth, and we don't feel the earth's rotation. So your point is...?

His point is that someone started a thread about a speedometer being two miles off and everyone is weighing in with their expert opinions, theories, anecdotes, etc, which is par for the course.  Soon, a reference to Jimmy Hoffa will appear.

 

[MARC Rider]

So why is it such a big issue to go above 83 mph? Superliners have a maximum speed of 100 mph and Viewliner baggage cars can hit 125.

My car can go 140 mph, or at least that's the maximum on the speedometer.  I have driven it at 80 mph on occasion.  However, the speed limit on the expressway that is part of my daily commute is 50 mph.  This is mostly due to the sharp curves and heavy traffic.  I have no idea how railroads set speed limits, but those two factors probably apply to railroads as well as highways.

 

[Thirdrail7]

  However, the speed limit on the expressway that is part of my daily commute is 50 mph.  This is mostly due to the sharp curves and heavy traffic.  I h

The Jones Falls, I presume?