This summer, near Orin Junction(?) south of the Powder River Basin in Wyoming, and last weekend, just north of Omaha, Nebraska, I saw UP trains on what appeared to be really close headways. The Wyoming coal trains seemed to be spaced only about 5 to 10 minutes apart. We saw 4 in about 20 miles. The Omaha trains, (actually in Iowa), were spaced about 10 to 15 minutes apart.
On a busy, fluid rail line, how close can the dispatcher run trains?
Well 15 miles apart sounds reasonable. If speeds were 60 mph (just a guess) and trains were 15 miles apart, and signals were 2-3 miles apart then then that should be pleanty safe (at least enough for a FY-Y-R and then some). On the other hand 4 in 20 miles is a bit dense, they were probably running on yellows and/or flashing yellows.
Minimum headway is a function of block length, which in turn is a function of:braking curves, which in turn are a mathematical formula unique to each railway signal department, which has at its independent values:
Average grades ascending or descending between block limits in the direction of travel
Maximum tons per operative brake
Maximum authorized speed on that particular line segment
Number of available aspects in the aspect progression, which varies depending upon whether there is a diverging route involved anywhere in the aspect progression.
Locations of interlockings and spacing between them, which throw into the aspect progression their own requirements for diverging routes.
Various constants determined by each railway that account for maximum braking horsepower of a composite brake shoe on the tread of a freight-car wheel within a given speed regime, etc.
The braking formula is used to determine the placement of wayside signals so that the heaviest possible train with the worst possible braking horsepower can never get an aspect that it cannot physically adhere to. (There is an exception called aggregate braking used when signal spacing can’t be worked out to adequate distances, or you can simply repeat the prior aspect, or both.)
In general in North American practice, trains are not significantly longer than the average block l
4 in 20 miles. If driving toward trains, then there is a deviation in timing. Standing still, four in 20 would be 5 minutes apart. Driving against the current of traffic would yield more time between trains depending on your speed (a variable) and more distance. ie. if you are traveling against the current of traffic at a steady 60 mph and the traffic coming at you is doing the same steady 60, and you meet a train every 5 minutes, then the actual time between trains is 10 minutes. .
I had already considered that. The Wyoming trains were about 5 minutes apart. I had been doing those story problems from hell at the time: “If loaded coal trains are heading east at about 50 m.p.h., and a family on vacation is heading west at about 60 m.p.h. through an incredibly heavy thunderstorm …” [:P] It was raining so hard, I couldn’t tell if it was single or double track at that point.
[(-D][(-D][(-D]
And school teachers everywhere are laughing, remembering untold generations of students in math class saying, “Why do I need to learn this? I’ll never need it after I get out of school!”
“…and you see”, as Albert would say, “it’s all relative.”[:D]
The train was 1/2 mile from the road crossing and traveling at 60 MPH.
From a distance of 1/3 mile the auto was proceeding, at a right angle, toward the crossing at 50 MPH.
Question: Did the driver get across? Yes, a white marble cross with his dates of birth and death on it.
RWM:
[Railway Man"]You’re probably looking for hard and fast numbers, so if we want all of our trains to run on nothing but green aspects in a four-aspect system (R, Y, FY, G), and our railroad is perfectly flat, and we have a maximum 153 TPOB, our block length cannot be less than ~ 4,000 feet (30 mph to 0 mph minimum distance between block signals) and the minimum headway is thus 12,000 feet. At 60 mph, or 5280 per minute, we have approximately 2.5 minute headways. But in the real world on a perfectly flat railroad, we will more likely have 8,000 foot blocks or 25,000 feet headways, because no one in their right mind is going to signal a railway these days with 4,000-foot blocks mile after mile. That equates to ~ 5 minutes at 60 mph.
RWM: Your post brings up a question that I"ve been waiting for for the right thread.
CSX’s A&WP subdivision had a signal upgrade about 16 years ago eliminating the code line but staying mostly automatic block. Signal blocks were lengthened to about an 2.4 mile or less length with one exception listed below. In 2007-08 CTC was completed from MP 6.3 in East Point to LaGrange, Ga. with the installation of two additional sidings being installed that were approximately 2.4 miles long. (Greentop and Moreland). These sidings were installed for the BNSF Haulage trains from the west coast to Fairburn (ATL) which number three or four a day each way being approximately 8000 - 10000 ft long. But here is the problem. From south to north there is an intermediate signal at MP 63.67; approach signal at MP 61.23; south end of Hogansville siding at MP 59.6; North end Hogansville 57.3; Then a cabin only (no signals and cabin identical to all other intermediate signal cabins) at MP 55.1; an approach signal for south bounds at MP 53.1; an advanced approach signal for Moreland at MP 50.4 (can show FY); approach signal for Moreland at MP 47.0
None of this stuff is that straightforward, and there are lots of unusual things that happen depending on how new signal installations are interfaced with older signal installations.
If someone would send me current pdfs of the track charts for this section and the appropriate pages from the Special Instructions showing the signal aspects and indications, I might be able to figure out what’s going on. But I mostly likely would need to see the signal line maps and aspect charts, too. Anyone have them they can email me?
RWM
RWM: May be able but will take awhile to get track charts but additional information is: The old code line system had spacing of about 1.1 miles between signals and the ABS upgrade 18 years ago had the average 2.2 miles( took about 2 mos from MP 25.8 to MP 69.1). That was when the 4.4 mile spacing occured from Hogansville to MP 53.1. The CTC upgrade took about 6 Months from the same points with all of it installed as RCL (Radio Control Line). Note signal locations essentially same locations as 18 years ago.
’ Wasn’t actually looking for hard and fast numbers. I was just curious how UP could send trains so close together, and what it took to determine the distances. I was pretty impressed that they could run them so close together, especially the coal trains.
Reading all the factors that go into determining the headway, what part will electronic(?) braking have on the system?
I did the math for nothing? [sigh]
Anyway, ECP might enable some small reduction in spacing, but probably not until the entire North American fleet is equipped, because block signal spacing is for the worst-braking train, not the best-braking train. PTC, on the other hand, might actually increase spacing because the braking algorithms have to assume worst-case-scenario, whereas a skilled engineer will usually know when his train will have a braking rate significantly worse than normal (e.g., packed snow on the brake shoes, wet leaves on the rail). We’re in a lot of discussions about that now.
Back to your observation, if you think about trains departing a terminal into CTC territory with nothing out on the main for some distance away from the terminal. In general terms, the first train to leave will leave when it gets a signal indication more favorable than stop and stay. As soon as his EOT passes the next signal, the first signal will be able to give an indication more favorable than stop and stay, allowing the next train to depart, and so forth. The first train will accelerate away from the second, and the second from the third, because it will get more favorable aspects, assuming all have like HPT, and if nothing interferes after a short period the first train will be separated from the second by three blocks, the second from the third by three blocks, and so forth. If the first train comes up to a less-favorable aspect than proceed at maximum authorized tr
[;)]
It was a funny line, but just doing the math in my head, he makes it across with 6 seconds to spare.
Not to pile on, but I got to the same conclusion, too. Details:
Obviously, the train gets there in 30 seconds (60 MPH = 1 mile per minute, so 1/2 mile = 1/2 minute = 30 seconds).
50 MPH = 50 MPH x 5,280 ft. per mile / 60 mins. per hour x 60 secs. per min. = 73.33 ft. sec.
1/3 mile = 5,280 / 3 = 1760 ft.
1,760 ft. / 73.33 ft./ sec. = 24.00 secs.
An easy way to make it work as intended is just to swap the speeds and distances, which are then probably more realistic and believable anyway - train at 50 MPH, car at 60 MPH. Then he runs into the side of about the 4th car behind the locomotives - about the trailing truck (see Mookie’s " ? ? " thread about the car that went under the tank car . . . ) Details: Car gets there 6 secs. after the train went past at 73.33 ft. sec. = 440 ft.of the train has gone by when impact occurs. Say 3 locos at 70 ft. long = 210 ft., so there’s 230 ft. of cars that have gone by. At 60 ft. per car, that’s near the trailing end of the 4th car, about 10 ft. in from the end = about where the wheel truck is.
So we could change the answer to, “No, he hit the truck !”, which would really mystify readers/ listeners unless they were as sick and twisted as we are . . .
Or, just change the answer slightly
The train spacing is governed by the dispatching computer, and is displayed in front of the dispatcher. The system will allow trains to run at medium speed (30) on “approach” indications (yellow blocks), or at restricted speed (15 or 20, depending on the rules) on “stop and proceed” indications. The exception is at interlockings, where red is “stop and stay”. The dispatcher monitors it all, and can override the computer if the situation requires. I’d be surprised if loaded coal trains are running at 60 MPH - they would create too much dust, lose product, and pound the rail silly. If the route is saturated with trains, they can only follow each other as closely as the TCS system allows. I would guess that coal trains five minutes apart, running 30 MPH, are actually about 2.5 miles apart. If everything is running smoothly (sometimes a big if), that’s a safe distance - more than the needed braking distance, and at least a full block apart. In all likelihood, those trains were running at 30 MPH on approach blocks, and were about as close togetrher as is safely possible.
Yes, but what sane driver is going to maintain his 50mph velocity after looking at the locomotive bearing down on the crossing?[:P] Not me.
One other moot point. If the crossing has any kind of protection beyond cross-bucks the driver of said auto is due a ticket and may owe the railroad a new gate.
UP and BNSF both permit unit coal (loads and empties) 50 mph. They attempt to hold that speed as much as possible on high-density main lines.
The dispatching computer does not govern train spacing. The field signal logic governs it. The dispatching computer is nothing but a means of relaying the dispatcher’s requests to the field. The dispatcher selects route and priority only. Everything else is in the field.
RWM
All class 1 RR’s UP/CSX/BNSF/NS run coal at 50 MPH, the FRA allows solid commodity trains to run at 60 MPH but RR’s run at 50 MPH to save fuel and reduce emissions. The trains you saw running in Iowa were most likely all running on clears at about the same speed, crews know what train symbols can do what speed and adjust accordingly some will bring there train down to a crawl not to accept an approach signal so they do not have to continue at reduced speed thru the entire block, which is usally two miles, coal trains at 130 cars approximately, with three units are about 7000 feet long, so they should never exceed any non-interlocking to interlocking block.