ATS vs ATC

Trains Magazine General Discussion
1

What’s the difference, pros & cons for these systems? how does each work?

2

ATS is simple to use, relatively inexpensive to install (at least trackside), and provides minimal protection against missed signals. If one does not acknowledge the trackside inductor, a penalty application of brakes occurs (it’s nice to have when running in fog so thick you can’t see past the nose of the unit). The downside is that it (the penalty application) tells you nothing other than the signal was something other that ‘clear’.

With ATS, there in a inductor-transmitter bolted to the ties about 20-50’ before a block signal. There is also a matching inductor mounted on one of the lead axles of the locomotive. When the locomotive-mounted shoe passes over the inductor, any signal other than ‘clear’ must be acknowledged by the engineer (by pressing a button or holding a lever) while passing over the inductor; failing to do so results in the penalty application, which takes about 120 seconds to reset. When the block signal shows ‘clear’, there is no need to acknowledge. The induction shoe on the axle and the trackside inductor-transmitter must have their height adjusted to a narrow margin–too close and physical contact might occur, wrecking the equipment; too far away and the inductor will not pick up the trackside current.

I don’t know much about ATC, except the system the CNW had on their Geneva sub was a real PITA to operate with (from what I’ve heard).

3

Whereas ATS is in effect only at lineside block signals, Automatic Train Control is a continuous system, with cab signals. If at any time the train speed exceeds that allowed by the signal indication, the system will sound an alarm and, unless the engineer brings the train speed into conformance, the system will make a penalty application of the brakes.

Johnny

4

ATS = Automatic Train Stop is simply if the signal is passed, then ==> the brakes are applied. No nuances or ‘fine-tuning’, lesser speeds, etc. - just a simple and blunt tool. ATC generally allows more precise gradations of speeds with the various signal aspects, and usually provides for cab signals as well to help the engineer by providing advance information.

Each system comes in ‘flavors’, and they are often incompatible and have different features. See the Wikipedia articles about each - usual disclaimers there apply - and the many other references at the following compendium of web links, being the Los Angeles County’s METRO Dorothy Peyton Gray Transportation Library [who even knew there was such a thing ?] at -

http://www.metro.net/about_us/library/train_controls.htm

  • Paul North.
5

If ATC is the system we’ve been discussing here in the past, the difference is night and day, at least as I understand it.

With ATS, you’re simply complying with the existing signal system. As long as the signals appropriately convey the necessary information, ATS will ensure the engineer is complying as he should.

ATC, on the other hand, uses GPS (and likely other sources - I’m no expert) to provide appropriate information to the crew. The information must be available on the system in order to accurately convey signals to each train. In theory, ATC could be applied to otherwise dark territory.

Feel free to correct my assumptions.

6

Larry / tree68 - No, what we’ve been discussing in the past is ‘PTC’ = ‘Positive Train Control’, and that is what you’re describing above.

Following is a brief and partial excerpt of the description of Automatic Train Control - ATC - from the Wikipedia page of the same title, which is linked’ at the METRO Library page that I referenced above, at -

http://en.wikipedia.org/wiki/Automatic_Train_Control

‘‘Its main advantages include making possible the use of cab signalling instead of track-side signals, and the use of smooth deceleration patterns in lieu of the rigid stops encountered with the older ATS technology.’’

That same site has many articles about PTC, for those who are interested.

Also, kudos [bow] to Chad for asking this question - there doesn’t seem to be a lot of info available - at least on-line - that discusses or informs on this seemingly routine subject - which is not ‘introductory’, but maybe the ‘intermediate’ course.

  • Paul North.
7

The biggest difference between ATC and ATS or coded cab signals (original UP) is that with ATC you can acknowledge the signal change AND have to slow down or stop. The other systems you can acknowledge the change and keep on going at track speed if you wanted.

I’m only familiar with the ex-CNW’s ATC. It uses a two aspect cab signal, Clear or Restricting. What happens when the cab signal changes from Clear to Restricting depends on the speed you’re travelling at.

Above 40mph you’ll get a high speed audible warning. You then have 6 seconds to place the automatic brake valve in suppression or you get a penalty (not emergency) brake application. The audible alarm (air operated whistle on older equipment, electronically generated tone on newer equipment) will sound continuously until speed is below 40mph. The tone changes to the low speed alarm and it may be acknowledged and will go silent. Our current rules require freight trains to stop when making a heavy brake application.

Below 40mph but above 22mph you’ll get the low speed alarm. It can be acknowledged but speed must be brought under 22mph within 70 seconds or you’ll get a penalty application.

Below 22mph but above 17mph you’ll get a different low speed alarm that can’t be acknowledged but won’t take the air unless speed goes over 22mph. Below 17mph you get the low speed alarm and can acknowledge it to silence it.

Intermittantly, about every 90 seconds or so, there will be an alertor type warning that must be acknowledged as long as you are moving.

I kind of simplified some of the terminology, but that’s the basics of our ATC. I know I wrote this before, but I gave up looking for it. Easier just to write it again.

Jeff &nb

8

ATC is a dream to operate under and hard to mess up unless you do something illegal. Jeff gave you the basics. Before UP, there were long long stretches without wayside signals, especially in Western Iowa. You just glided along until ATC told you otherwise. When track maintenence was poor and you had rainy weather, you would get false restricting signals. But that was the extent of it.

Also early on, with the SD90/43’s, there was a software glitch that allowed the track sensor to read AC signals from the motors, giving you false restrictings.

But like guys told me, it was failsafe compared to line-side signals.

9

Still do get a lot of “rain control” on the east end. Doesn’t even have to be raining, just a lot of humidity.

Once in a while there will be a dead track thru the entire block. When reporting it, almost always the dispatcher asks what the weather is like. (I had locomotive maintenance ask me what the weather was like one time when having electrical problems on a fairly new unit.)

Jeff

10

ATC is not based on GPS. It’s an older system based on track circuits. The new PTC systems, when deployed, will use GPS.

The problem with the ex-C&NW ATC system is that it’s only a two aspect system (basically “go/no-go”). As such, it requires heavy brake application when the system drops to restricting.

11

You’re absolutely right - my bad. Too many acronyms.

12

Did the CRIP have either system ? If so, where was it installed ?

13

The RI had cab signals and a different form of ATC then the CNW’s. It was installed between Blue Island and Rock Island on the Illinois Division.

Jeff

14

This is the mounting system used by the Southern and the IC, among other roads. There is another system, which I believe that the L&N and ACL used. As well as I could tell, the running rails carried the trackside signal, and the pickup was in/on a rod that extended across the rails ahead of the first truck (on diesels).

Another danger of the truck mounted pickup was that you had to be sure that it was fastened securely, else you could have a pickup coil flailing about and taking switch stands out; the Southern had this experience north of Birmingham, on the AGS, in the late sixties or early seventies. Not long thereafter, the Southern petitioned to remove the entire ATS installation from its system, particularly since no train was then allowed to run faster than 1 mph over the ICC speed limit allowed without ATS, ATC, or cab signals.

Johnny

15

I have a few questions about the former CNW ATC. I have been curious about these for years.

  1. When the train gets a flashing yellow block signal, what is the ATC aspect?

  2. When a train gets an approach diverging (yellow over yellow?) what is the ATC aspect?

  3. When a train gets a diverging clear block signal (red over green) what is the ATC aspect.

  4. The former CNW has (or at least had) two CTC systems between Chicago and Council Bluffs, the 50s era east of Nelson, the 60s era west of Dennison. Now this line has 90s and 2000s UP CTC over much of the line. Did/do the ATC aspects (in relation to the block signal aspects) vary depending on which era CTC installation you are on?

Thanks to anybody who takes the time to answer these questions.

16

I can only answer for the territory between Clinton (actually Rte. 84 on the Illinois side) and Council Bluffs. There may be special circumstances over on the Illinois side I’m not aware of.

  1. Depends. Some of our power crossovers (the ones good for 40mph) only have a flashing yellow to provide warning of a crossover move. If you are lined to crossover the cab signal stays clear. If not, it goes to a restricting. At other flashing yellows, except for a couple that are wired different, the cab signal drops to restricting. Our rules state that if the cab signal clears up and you could crossover at the next signal, the speed must not exceed the speed the crossover is good for until you see you aren’t crossing over.

  2. At a yellow over yellow it stays clear. That indication means you are diverging at the next signal and not to exceed the allowed speed for the crossover. Remember, when the cab signal and wayside signal disagree, you go by the most restrictive indication.

  3. Cab signal remains at Clear.&n

17

Jeff:

Thank you so much. I have wondered about those thing for decades

18

Jeff, your responses for #2 and #3 also are true on this end of the pike–Approach Diverging and Diverging Clear both get clear cab signal indications for Park Interlocking, in Elmhurst. That’s about the only one I’ve encountered on any regular basis.

19

The false restricting signal problem occured on all AC locomotives with Union Switch and Signal Cab Signal systems, GE and EMD. It wasn’t caused by a software glitch, it occured when the traction motor drive frequency matched the cab signal carrier frequency in the rail and made the signal pulses undetectable. The cab signal pick-up bars are directly in front of the first motor and were saturated by the motor drive frequency. The signal carrier frequency on UPRR CCS is 60 HZ, the cab signal would go to restricting at 22 mph, the cab signal carrier frequency on CNW ATC is 100 HZ and would go to restricting at 38 mph. US&S never did resolve the problem, however Harmon (now GE Global Signaling) did and got all of the Union Pacific cab signal businss.

20

Thanks for the replys everyone. I haven’t been able to post till today.