In the past I have made reference to various "two aspect" cab signaling systems, specifically those used on the Illinois Central (since retired) and the former Chicago & North Western east-west main line, now operated by Union Pacific. Aside from the cab signal display of current Union Pacific locomotives this two aspect system can be seen in the cabs of old METRA locomotives and Illinois Central signal rule charts.
The cab signal "code" (pretty much the presence of an AC current frequency or even a DC voltage), is transmitted from any signal point displaying more favourable than approach. Passing a yellow signals will cause the cab signal to drop to Restricting and the train will continue on at Restricted speed until the cab signal returns to Clear. To ease the confusion between wayside and cab signals, both the CNW and IC used this system without fixed wayside signals except at distants and interlockings.
Alright, now I'll bet you are just thinking this system is horribly inefficient as trains will be crawling at Restricted speed instead of a less odious 30mph Approach. The key consideration here is to remember the braking time and for most freight trains, getting slowed down from MAS to Restricting will take a good chunk of the Approach block. Let's see what the GCOR Rulebook has to say on this issue.
Basically if you are traveling over 40mph, reduce to 40mph and then you have 70 seconds to reduce speed to Restricting (20mph) or at least be making a sufficient brake pipe application to reach that speed after 70 seconds. It's not as efficient as a traditional 3 aspect system, but it likely won't penalize a typical train more than a couple of minutes. The situation is a bit dicier approaching diverging routes and, especially where no waysides are present, the engineer has to pretty much be prepared to advance on the slowest route unless the home signal can be otherwise made out.17.5.1: Over 40 MPHThe high speed whistle will sound when the speed is more than 40 MPH when the cab signal changes to a Restricting aspect.
- Move the brake valve handle to SUPPRESSION within 6 seconds to prevent a penalty brake application.
- When speed is reduced to less than 40 MPH, the high speed whistle will stop and the acknowledging horn will sound.
- Acknowledge this horn. If the cab signal continues to display Restricting, speed must immediately be reduced to restricted speed,
If restricted speed is not reached within 70 seconds after the acknowledging horn was acknowledged, a penalty brake application will occur unless the brake valve handle is in SUPPRESSION17.5.2: Under 40 MPHThe acknowledging horn will sound if the cab signal changes from Clear to Restricting when the speed is under 40 MPH.
- Acknowledge the horn within 6 seconds to prevent a penalty brake application.,
- If the cab signal continues to display Restricting, train speed must immediately be reduced to restricted speed.
If restricted speed is not reached within 70 seconds after the acknowledging horn was acknowledged, a penalty brake application will occur unless the brake valve handle is in SUPPRESSION.
Ultimately the system works, and although it dis not as advanced as the PRR version, it did save a lot of expense equipping locomotives with code following relays. The IC eventually removed it's installation on the Champlain District sometime in the late 80's or early 90's as Canadian National came on the scene. It also goes to show that the engineer doesn't need to know he's approaching an occupied block, just sufficient time to show down before entering the occupied block.
If you look at the 1992 CNW track charts for the main line through Iowa it looks like the interlockings had wayside distant and home signals. When UP took over they made the whole line CTC and added wayside automatics that can show advance approach. These now have PTC antennae so the old cab signaling may be dead in Iowa. When Amtrak had to detour over CNW in Iowa after the 1993 floods, they would use ancient Metra cab-units as pilot locomotives for the cab signals.
ReplyDeleteSafety systems have to be formally abandoned and the FRA is unlikely to do so until the PTC system is proven and reliable. Keep a look out if the PTC antennas are at automatic signal locations or just at the interlockings. NS is using cab signals, where equipped, as an alternative to a full time digital radio link. Much more reliable. The CNW ATC system could suppliment the PTC in the same way. If a train sees an ATC "clear" it wouldn't need a PTC signal.
DeleteGreat article Jersey Mike! I just ran across another 2 aspect cab signal system that made all the way into the early Conrail era. On the ex-New Haven of all places on the Hartford line from New Haven to Springfield.
ReplyDeleteI just recently purchased Conrail's first employee timetable of their Northeastern region. A lot of people don't know that Conrail briefly operated the Northeast Corridor from April until September 1976. In there they have a section on cab signal rules.
I'm quite familiar with the NH 4 aspect cab signal system on the Shore Line (essentially the same as PRR but with G/YG/Y/LW colors rather than position lights) but was surprised to see mention of a 2 aspect system on the Hartford line with only a Green Clear aspect rule 281 and a Lunar White Restricting for all other aspects. A bit of research found that this system was installed in the 20s on one of the two divisions mandated by the ICC. Why the HN chose 2 different systems is unknown. Both were built by Union Switch & Signal.
Interestingly, Amtrak's 1st NE Corridor ETT of October 1976 only mentions the 4 aspect Shore line system. So presumably either Conrail or Amtrak dismantled it after April but before October.
I assume the NH 2 aspect system worked the same way as the IC/CNW systems you mention above.
ReplyDeleteOn the UP, ATC is not used with PTC. Trains operate with only one system active, although lead engines in ATC territory must be equipped and have passed an ATC departure test. Once PTC has passed it's certification, look for ATC to be discontinued. They already are not maintaining the ATC infrastructure.
ReplyDelete