Sunset limited top speed

[john h]

I always thought too speed was 79 but headed to El Paso along I10 in Texas seems like we hit 81 according to Waze

And extra vibrations it seems in coach

 

[cpotisch]

A GPS on a smartphone is not nearly accurate enough to calculate speed within  two mph. The Sunset maxes out at 79.

 

[john h]

Thanks wasnt sure how accurate Waze is I know in a car it's very accurate

 

[Steve4031]

There are usually uphill and down hill segments on an almost continuous basis.  The engineer and controls must be pretty precise to never go over 79 mph.  It’s amazing the skill these people have running the train.  It’s easy to take for granted but should never be taken for granted.  

 

[PVD]

Someone else please jump in, but I seem to remember a small margin of error being allowed. So hitting 80 for a few seconds would not cause the end of civilization.

 

[crescent-zephyr]

The speedometers on the engine can be off, allowing the engineer to see 79, but the actual speed to be 81. 

On an old pentrax video I have of a cab ride on the nec, the engineer is seen with a stop watch comparing the time between mileposts with the speedometer on the locomotive 

 

[john h]

It wasn't really that much of an issue just wish we were on an earlier schedule but I know track work comes first

 

[TinCan782]

Not unusual. I've seen 80-81 on my Garmin GPSmap 64s handheld GPS. There is an allowable "tolerance" and, as mentioned above, its not unusual to have discrepancies between your device, the speedo in the loco and actual.

 

[PVD]

That triggers a few questions. Assuming that speed indication is extrapolated from the rotation of something (axle/wheel) and not radio/detection based, would there not be some error inherently from wheel wear? Would it be too small to measure, and/or  would you need to re calibrate after installing trued wheels? I know that if you change tire size in a car you most certainly can cause speedometer error. Some food for thought, while I wait for mine to be delivered.

 

[Amtrak706]

That triggers a few questions. Assuming that speed indication is extrapolated from the rotation of something (axle/wheel) and not radio/detection based, would there not be some error inherently from wheel wear? Would it be too small to measure, and/or  would you need to re calibrate after installing trued wheels? I know that if you change tire size in a car you most certainly can cause speedometer error. Some food for thought, while I wait for mine to be delivered.

It is from wheel rotation. As far as I know what you are describing does not happen, and I don’t think an allowable amount of wheel wear would really affect a speedometer. And regardless of the accuracy of the locomotive’s speedometer, the overspeed kicks in at 83 and engineers pretty regularly let the speed creep up to 80 or 81 for a little bit as the train comes down a shallow hill. They do generally stay pretty close to 79 but it’s definitely not pegged there the whole time, the speed might drop down to 77 or 76 as the train comes up a hill and the P42s are loading amps at an anemic pace to creep back up to 79.

 

[Thirdrail7]

 Assuming that speed indication is extrapolated from the rotation of something (axle/wheel) and not radio/detection based, would there not be some error inherently from wheel wear?

Yes, it happens quite a bit.  This is a huge problem with GPS based PTC that suffers from time lag and a speedometer based upon wheel rotation.

 Would it be too small to measure, and/or  would you need to re calibrate after installing trued wheels? I know that if you change tire size in a car you most certainly can cause speedometer error.

It depends on the difference. It can be negligible or can cause problems such as penalties, speed control issues and other major issues. With most things being computerized these days, it is important to measure and input the PROPER wheel diameter in the system under normal circumstances and  especially after you true the wheels.

 

[PVD]

The laws of math and physics made me think so, but hearing it in real word framing helps clear the clutter of my mind. (Speaking of which - I'm toggling back and forth between "A Beautiful Mind" and a Paul Simon Concert from 1991 that I was at....) Chevy Chase showed up for "You can Call Me Al"

 

[Acela150]

Someone else please jump in, but I seem to remember a small margin of error being allowed. So hitting 80 for a few seconds would not cause the end of civilization.

Correct. The overspeed cutoff is 83 mph. 

The speedometers on the engine can be off, allowing the engineer to see 79, but the actual speed to be 81. 

On an old pentrax video I have of a cab ride on the nec, the engineer is seen with a stop watch comparing the time between mileposts with the speedometer on the locomotive 

Correct as well. I had a locomotive at NS that the speedometer was off but a second speedometer know as the "LSL" Locomotive Speed Limiter. Was correct. There is something known as a measured mile. Which has been measured as exactly one mile between mileposts. The engineer can use a stop watch to see if the speedometer is correct. 

I should also mention that things like this topic are what Railroaders don't like about Railfans. And when I worked for the RR it drove me up a wall cause some rail fans think that they're know it alls. 

 

[cpotisch]

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.

 

[PVD]

Measured mile was pretty useful in speeding enforcement on highways also....

 

[PVD]

A lot of reasons, geometry, track conditions, traffic....those are the most obvious......

 

[niemi24s]

To put this all into some sort of perspective,  when timing  a 79mph train (or anything else) over a measured mile an error of 1 second introduces a calculated speed error of about 1.7mph.

 

[TinCan782]

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.

Maximum speed determined by track conditions, etc. (the host RR, FRA standards, etc.), not necessarily the equipment. Segments of the Pacific Surfliner and SW Chief are authorized 89 MPH.

 

[Tony in Ann Arbor]

Track speed limits set by FRA based on track class:


49 CFR § 213.9 - Classes of track: operating speed limits.

• CFR
  
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§ 213.9 Classes of track: operating speed limits.
(a) Except as provided in paragraph (b) of this section and §§ 213.57(b), 213.59(a), 213.113(a), and 213.137(b) and (c), the following maximum allowable operating speeds apply -


[In miles per hour]


Over track that meets all of the requirements prescribed in this part for -


The maximum allowable operating speed for freight trains is -


The maximum allowable operating speed for passenger trains is -


Excepted track


10


N/A


Class 1 track


10


15


Class 2 track


25


30


Class 3 track


40


60


Class 4 track


60


80


Class 5 track


80


90

 

[Acela150]

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.

Simple.. Look at how many Long Distance trains are run on tracks owned by Freight Railroads. They're not going to install Class 5 track for a once a day train in each direction. Especially when Freight Locomotives are capped at 70mph. The NEC is owned by Amtrak. So they can put the high class tracks in cause they own it and maintain it for PAX service. 

 

[PRR 60]

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.

 

[PVD]

Max track speed is only one factor in speed limits. There are plenty of speed limits imposed for a variety of reasons where max speed for a certain area may be well below what the track is rated for....Think of a train derailing going too fast on a curve 

 

[Mike G]

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 .

 

[TinCan782]

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 .

Waze (and other smartphone apps) is dependent on the quality of the GPS system in your phone. The quality of the GPS signals can be affected by a number of things including how much sky (how many satellites/how much of the constellation) can the GPS "see". 

 

[Mike G]

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

Yes I’m very familiar with those limitations and geometry, being on one of USAF test teams in the Pacific for INS and later GPS integration programs. Before they were useable busterd Hawaiian, Guam and Japanese ADIZ many times even wished we had a Sexton.  Bendex and Honeywell was onboard fine tune it. There were a couple of times we weren’t sure where in the hell we were until ATC called us with radar contract. There’s a whole lot to it before it comes out of the box plug n play.  You want to have fun with it .... take it across 0* Latitude the 1st time.

seeing your patch were you a River Rat or Swift Boat ? I was a FAC (O-2A) we might have worked together when we were young HA !