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- Jul 16, 2010
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From Amtrak's web site Train tracker this morning.
And what the engineer's job depends on.There is a just a bit of wiggle room on the overspeed governer and 2 mph over doesn't trip it (although that might be about it). Also, I don't know if that reading is tied into the locos speedometer or whether it is calculating it based on GPS. The two may be the same (although likely GPS is the more accurate), but what the loco says is what the engineer is controlling.
On the otherhand, if one is going through pretty country, 79 just might be a little too fast... but for boring countryside, or at night: let it flyAcela-like 150 mph would be great, but I would be nearly as happy just to see a SUBSTANTIAL portion of Amtrak's service being able to go 95 mph. 110 would be phenomenal!
I thought that PTC would have made a bigger difference, sooner. Obviously it is a complicated issue, but 79 mph is pretty darned pokey.
In a previous discussion, I was of the impression that speed was deduced via radar Doppler shifting under the train using the ties or metal parts as reflectors... the comment then was that with wheel slippage, axle rate as not indicative.... but than again, could be misremembering.How does the train know how fast it is going? Rotations per minute of a axle ? How much metal can be worn out on a wheel to give a difference of a mile or two?
Yes, I have had GPS show slight movement when standing still. I have been told that when driving in a car, my speedometer shows 65, but the GPS says 61, go by the GPS.
Bruce-SSR
Is that the GPS that makes you make wrong turns?? LOLI am on 98 right now and several times my GPS indicated that we were traveling at 81 mph.
The really "good" GPSs make you turn onto RR tracks and right into an oncomng train! :giggle:Is that the GPS that makes you make wrong turns?? LOLI am on 98 right now and several times my GPS indicated that we were traveling at 81 mph.
Whether a wheel is slipping or not is determined by comparing the Doppler radar determined speed against the speed determined from angular velocity and radius of the wheel (roughly speaking).In a previous discussion, I was of the impression that speed was deduced via radar Doppler shifting under the train using the ties or metal parts as reflectors... the comment then was that with wheel slippage, axle rate as not indicative.... but than again, could be misremembering.
But bottom-line: the Doppler speeds is taken as ground-truth (ie, the reference). Correct? And I suspect it is/can be quite accurate, as in several significant digits?Whether a wheel is slipping or not is determined by comparing the Doppler radar determined speed against the speed determined from angular velocity and radius of the wheel (roughly speaking).In a previous discussion, I was of the impression that speed was deduced via radar Doppler shifting under the train using the ties or metal parts as reflectors... the comment then was that with wheel slippage, axle rate as not indicative.... but than again, could be misremembering.
Suspect CYAitis is directly proportional to litigation experienced (subject thereof) and sum of judgment/settlement payouts.I'm no scientist so I'll leave stuff like this to the experts of which this forum has many!
Isn't it amazing how in the old days railroads prided themselves on their OTP and engineers and conductors ran their trains with just employee timetables, pocket watches,basic signal systems, manual switches and written train orders??!!!
I have heard detectors transmit "eight zero mph" and "eight one mph" on occasion and to my knowledge nothing happened so there must be a little leeway, at least for momentary fluctuations.There are or were designated mileposts between which time was required to be checked on the watch for comparison with the milepost. Also the employee timetables have or had on them a list of speeds versus seconds per mile.
In years past the speed limits were much less strictly enforced. Now they are very strongly enforced. When you see a number above 79 on the GPS, the most likely answer is that the GPS is off. ZERO leeway is the norm today, and that is enforced with the feds looking over your shoulder.
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