I thought the speed limit was 79?

shop deals on amazon
Shop deals on ebay
Advertise with us
Amtrak Unlimited Discussion Forum

Help Support Amtrak Unlimited Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Status
Not open for further replies.
Few stretches of track are perfectly level. Over a given mile or so, there can be some significant variations of grade. The dispatcher expects the engineer to maintain track speed to keep everything on time. If the engineer maintains maximum track speed on a slight upgrade, his train will naturally begin to exceed the maximum as he crests the grade and starts down the next slight downgrade. Extremely fine control using the brakes is a wonderful goal, but not often achievable, even by the very best engineers, so a certain amount of leeway is given to the engineer to allow for this. It's just physics.

I remember timing mileposts while riding in the boat-tail observation car on the rear of the old Seaboard Silver Meteor in the spring of 1967, cruising through Central Florida. Pretty much a steady 90 mph.
 
That long documentary about Empire Builder that someone shared few days ago had the engineer explain to the narrator that the speed cut-off is set for 82 mph. He showed a sample by pushing the train to 83 mph and the buzzer started beeping. Needless to say he brought it back within limits immediately.
 
As has been said by others, 1-2 MPH wiggle room probably exists in practice simply because equipment is not infallible. Even under the best conditions, well-used equipment is going to have some inaccuracies. But the main explanation is probably "jumpy" GPS measurements.
 
Just like driving your car, it is very tedius to maintain an exact speed on a locomotive over a period of several hours. As has been said, the variations of grade make it a constant struggle to keep the needle glued to an exact speed. So if a train loses or gains a couple of mph here and there, it is understandable.

Even cruise control on cars sometimes will gain or lose for a few seconds, before correcting itself, and of course there is no cruise control AFAIK on any locomotive...
 
the overspeed is set at 83. My iPhone GPS Speed app clocked the EB at 82 on quite a few stretches of route.
 
That's good to hear....when driving, constantly having to look down the road, and then at your speedometer, and the resultant refocusing of your eyes from far to near vision and back, is probably a cause of more fatigue on a long trip, then pressing down on the accelerator. So cruise control is a wonderful stress-reliever. And no human can match a good cruise control for maintaining an exact speed over a long haul.

I am surprised somewhat, that the FRA allows the device, simply because it allows the engineer to not maintain a constant vigil. But then again, they do have those "alerter's", that do insure that the engineer has not drifted off to sleep.....
 
If you look at pics of the F40s you can see a big cord coming off one of the front wheels. That is the speed recorder. The wheel itself has a toothed gear which is what the recorder looks at to determine the speed. The F40 did not have a radar.

The current GE locomotives have speed sensors built into each traction motor so speed of each axle is monitored and is generally much more accurate than the old recorder like the F40 had- assuming the wheel size was programmed into the computer correctly. There is a doppler radar aimed at the ground as well as Jis already mentioned.

FRA regulations say the speedo can be off +/-3mph at speeds of 10-30mph, and +/-5mph above 30.

Tolerance of speeding varies on different railroads. The NS will discipline for even 1mph over the speed limit. Others will allow a few mph over if you take corrective action. I'm not sure how strict Amtrak is about it. As far as the FRA is concerned you aren't allowed to go 10mph over (that causes an engineer to be decertified for a specified amount of time). Going 9mph over the limit the FRA wouldn't do anything, though the railroad probably would.

I've been told by track workers that whatever speed a curve or switch is rated for is designed so that a train going double that speed normally won't derail but I'm certainly not going to try to find out!!
 
So - there's various speed limits on various tracks.

On LongDistance Amtrak (not NEC, not HSR) speed, by regulation is "under 80 mph" (with few exceptions)

The max is 79 mph, on tracks that can take that speed.

It's good to know that there's at least 4 ways to measure train speed. Namely (Can't do bullet points here)

Time between mileposts.

Rotational speed of the axle ( I've seen the magnetic pickups on axles, thank you very much)

GPS - which is good to a few meters for slowly moving objects, don't ask me about microsecond timekeeping - works for stationary objects. You want more on GPS specs- ask NIST - int all that it's cracked up to be

Doppler Radar -- looks real good for measuring speed, not location .

Please remember the defining proof of our era - the Heisenberg Principle -- !!

If you care about where you're going, you can't know when you get there.

If you care about how fast you're going -- you cant know where you'll get to.

a

Proven and tested by Quantum Mechanics -- they've been totally right so far.

And proven by my experience hitchhiking, or any other mode of travel.

You who care might guess what it means.

For travellers --
 
NW cannonball said:
Please remember the defining proof of our era - the Heisenberg Principle -- !!

If you care about where you're going, you can't know when you get there.

If you care about how fast you're going -- you cant know where you'll get to.

a

Proven and tested by Quantum Mechanics -- they've been totally right so far.

And proven by my experience hitchhiking, or any other mode of travel.
Click to expand...
Figuratively speaking. Also distance and time are not canonically conjugate, so Heisenberg's Principle does not apply to them directly. Time and energy are canonically conjugate so the uncertainty principle applies to that pair.

The actual Heisenberg Principle of Physics, applies in energy/time and momentum/distance (canonically conjugate variables) ranges that are way outside of what anyone is able to measure or observe in day to day life. That is because Planck's Constant "h" is 6.62606957 × 10-34 m2 kg / s. and the uncertainty is only of that order of magnitude. Heisenberg's Uncertainty principle for distance/momentum says:

bbb1b74b511f868d0882a668de23c111.png


i.e. the product in the error of measurement of distance and momentum is of the order of Planck's Constant. (h cross is just h divided by 2*pi).

You who care might guess what it means.

For travellers --
Click to expand...
For the traveler, as long as it involves AGR he does not care about any other principles :p
 
Status
Not open for further replies.

Latest posts

Back
Top