The “After PTC” article in the Feb Trains is interesting. But …
It states that moving blocks would be very beneficial to unit coal trains, whereas intermodal trains do just fine with the current fixed-block system.
Why the heck would that be? Why does the type of freight matter?
Is it because a long coal train is slower and more prone to delays, while an intermodal train’s pace is more predictable? That’s all I can think of; and I’m not sure what I just said about those two train types is even true.
Intermodals are already given preference in Dispatching - ie. getting lesser priority trains in the clear to allow the Priority trains to be operating on clear signals. Lower priority trains, in many case are operating on less than clear signal indication. Rolling ‘blocks’ would give the lower priority trains to operate more frequently on ‘clear blocks’. At least that is the theory. In actual practice???
One thing that gets overlooked by many in the operation trains in signalled territory.
When a train is Overtaken by a higher priority train, it will not leave the siding immediately after the priority train has passed - to do so would have the train leaving the siding operating under the requirements of a Restricted Proceed signal indication - operating at 20 MPH or less and WITHIN 1/2 the range of vision looking out for a train or other obstruction ahead until they get a more permissive signal indication at the next signal.
Normally the overtaken train will wait until they get some form of a Approach indication, that permits them to operate at 1/2 the maximum authorized speed not exceeing 30 MPH and being prepared to stop at the next signal. The Approach form of signal indication tells the overtaken train there is NO TRAIN or obstruction between it and the next signal - a much ‘easier’ operating condition.
To get a Clear indication there must be at least TWO (and in some systems more) signal blocks between the two trains. Once upon a time signals were spaced at a nominal mile or so; when the carriers started operating larger trains they began spacing signals at a nominal two mile distance, in the 21st Century the signal spacing has been extended to a nominal three miles between signals - the spacing is to allow for nominal, non-emergency, braking distance. PTC enforced braking distances may be longer.
The higher priority train is moving north and lower priority train is heading south. Why hold the lower priority train once the rear of ther higher priority train has cleared the switch and is proceeding north?
Ans: Once the higher-priority train has cleared the switch and the operator has verified that it has switched and locked properly, you may assume that the lower-priority train will proceed just fine, as the block into which it is proceeding can be assumed to be vacant.
What Balt was describing is a different situation entirely, looking at the other end of the siding with both trains proceeding the same way. In an absolute-block system, the lower-priority train would have to remain in clear until the higher-priority train completely cleared the block past the end of the siding – only at that point could it start more than a little acceleration. CBTC can be arranged to gauge the actual separation based on speed and acceleration as well as default physical distance, so what happens is that the switch traverses and the lower-priority train can proceed with ‘as much dispatch as it can muster’ just as if it were entering a clear block, until the speed of the lower and higher priority trains become equal.
In practice there would be some leeway allowed for emergency braking or catastrophic derailment of the ‘high-priority’ train in the example, more of course if the ‘continuous’ were in some sense functionally intermittent in speed tracking, or some of the NAJPTC engineers left the food-service industry for another try at train control and forgot about tracking the back end speed as well as the front.
But for slowly-accelerating coal trains trying to save fuel, being able to start rolling up to hopefully-sustainable track speed early is a meaningful time saver. And once that train is up to track speed, its inertia will likely help it on even an undulating profile to maintain 'one-sp
I was not impressed with the article. There were things that the author didn’t get quite right in current PTC operation and some of the subsystems that we have. I’d have to get out the article for specifics.
The theory is that rolling/moving blocks allow trains to run on closer headways. That the point of where authority to move ends will be at (or more likely close behind) the end of the train ahead, instead of a fixed signal boundary point. The moving boundary is going going to be continuously calculated, including the changing braking distance to the end point. I’m not sure that going to moving rather than fixed point boundaries will make that big of difference. I think it will cost more to get that capability than possible savings from closer headways will actually save them.
I would opine that the place moving blocks will make a difference is on heavily used lines, where the reduced headway between trains will increase capacity.
For simplicity’s sake, moving blocks would be a lot like driving your car - you hopefully leave a suitable space between you and the car ahead. As the speed goes up, so does the distance.
OTOH, if you are the only car in sight, your speed is governed by the posted speed limit and the abilities of your vehicle.
If you watch the various train cams around the country, you’ll rarely see two trains on short headway. More often, they are an hour and more apart in any given direction. On a single track line, sans fleeting, rolling blocks would make virtually no difference.
I enjoyed reading it. But there were several places were he stated X will mean Y. Or A will facilitate B. And my brain was like “well, you’re saying that, but you’re not showing me.” So I had no idea how much of value was really there. Seemed like generalities/suppositions/predictions, but not a lot of clues to help someone like me to understand. Technical folks and current railroaders certainly would understand much more, but I’m not surprised to hear you say some of it was inaccurate.
OK, let’s presume that they eventually get this whole PTC/moving block thing working. There will be bugs and those bugs will need to be worked through. This happens with everything. While this is going on, many people will be complaining about “Change”. People don’t like two things; 1) Change and 2) The way things are now.
So anyway, this whole moving block thing will require ultra-reliable communication between the lead train and the following train. If the lead train goes into emergency the following train needs to react immediately. So, if they get that worked out to 99.999% reliability, what can we do from there?
Let’s talk about a set out at Cedar Rapids, IA. (My favorite “For Example” place.) Leave us just say that we’ve got a westbound out of Chicago for North Platte carrying a Cedar Rapids set out block. (OK, just to be clear, the word “Block” can have at least two meanings in railroading. As used above it means a section of track. As used in this paragraph forward it means a group of freight cars. Got that?)
Current, and forever past, practice requires the entire train to stop. Then a “Ground Person” (gender neutral), or “Ground Persons” must manually uncouple the freight cars at the end of the block (group of cars). Leave the rest of the train sitting still (I hate that) and move forward past a switch.
Then the switch must be changed so that a reverse movement will put the set-out block on a different track. Then the lead locomotives must reverse and shove the set-out block on to another track. Then the locomotives must be uncoupled by a ground person from the freight cars. Handbrakes must be set. Then the locomotives must move forward past the switch. The switch must ag
I’ve done moves where you pull into a yard, a yard crew (which PSR/some style management doesn’t like) - grabs onto your rear end set out - a utility (again, PSR and certain managers hate these) then moves and rehangs the marker and launches you out on your way.
Can even do the opposite for a pickup, or a modified way to do both.
Is a really quick process - road train takes a couple minute pause - and everything is on its way. It’s amazing what (and how fast) you can do when you have a couple decent yard crews or utilities, and aren’t relying on a 23,000 foot train to do all its work by itself.
All the electronic nannies and toys aren’t going to replace a pair of boots on the ground. Period. That’s the fantasy.
And Greyhounds, pickup in Ceder Rapids is simple with your concept
The through train from Omaha stops for a few minutes while the Ceder Rapids power has the switch benind the train thrown, couples on to the end of the train, with the former Fred de-activated and the one at the end of the Ceder Rapis block activated, and the Ceder Rapids power is the distributed power to Chicago.
Fine if PTB has that reality accounted for in its software.
For decades B&O and later CSX had a scheduled train totally based on rear end setoff. Train 396 which in later CSX days became 296, originated in Flint MI with autoparts for the GM Assembly plants in Baltimore and Wilmington. Train operated with a caboose as the rear Wilmington car that was ahead of all the Baltimore cars, with the required caboose on the rear. Train arrived Bayview Yard in Baltimore for a crew change and set off - Bayview yard crew was sent out on the other Main to make the cut behind the Wilmington caboose and the train started to pull picking up the Conductor & Flagman on the Wilmington caboose on the fly as it passed BA Tower. Arrival to departure was normally 10 minutes. After cabooses were removed from trains the Bayview yard crew would make the cut behind the last Wilmington car and rehang the EOT from the rear of the Baltimore’s.
Today neither Wilmington nor Baltimore have GM Assembly plants.
OK, let’s presume that they eventually get this whole PTC/moving block thing working. There will be bugs and those bugs will need to be worked through. This happens with everything. While this is going on, many people will be complaining about “Change”. People don’t like two things; 1) Change and 2) The way things are now.
So anyway, this whole moving block thing will require ultra-reliable communication between the lead train and the following train. If the lead train goes into emergency the following train needs to react immediately. So, if they get that worked out to 99.999% reliability, what can we do from there?
Let’s talk about a set out at Cedar Rapids, IA. (My favorite “For Example” place.) Leave us just say that we’ve got a westbound out of Chicago for North Platte carrying a Cedar Rapids set out block. (OK, just to be clear, the word “Block” can have at least two meanings in railroading. As used above it means a section of track. As used in this paragraph forward it means a group of freight cars. Got that?)
Current, and forever past, practice requires the entire train to stop. Then a “Ground Person” (gender neutral), or “Ground Persons” must manually uncouple the freight cars at the end of the block (group of cars). Leave the rest of the train sitting still (I hate that) and move forward past a switch.
Then the switch must be changed so that a reverse movement will put the set-out block on a different track. Then the lead locomotives must reverse and shove the set-out block on to another track. Then the locomotives must be uncoupled by a ground person from the freight cars. Handbrakes must be set. Then the locomotives must move forwa
Beverly (Cedar Rapids), where trains go to die. Mainly because most of the trains that need to work all show up at the same time. Even when they try to stagger call times at Boone to space trains.
Then a 10000 ft manifest picks up another 2000 ft solid block off the south side and another 2000 ft solid block off the north side. Might have to reposition engines to new DP configurations. Now you have a 14000 ft train that needs an initial terminal air test for the entire train. Better have a relief crew ready.