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- Thread starter drum118
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TOareaFan
Superstar
So it is just a switch that has a speed limit? Is that much of an issue here? Would trains not, naturally, be going slow here anyway?
squircle
New Member
I didn't want to make too big a deal about it in the tweet, because I don't think it's that big of an issue. At the east end, there's a #20 switch good for 45 mph. But at the west end, it's either a #10 (15 mph) or a #12 (25 mph) purely based on the signalling gantry. (In theory I could've counted the number of ties to get a length measurement but they were covered with fresh ballast, and it's tricky to ballpark.) There's the obvious problem of the bridge pier being in the way, but there seems to me to be quite a bit of extra room that's going unused.
You're right in that trains would either be slowing to or accelerating from a stop, but IMO every little bit counts. Given that the zone speed drops around Snake, it's not going to make or break a timetable. But I'd certainly be interested to know what design options were considered, and what's possible given the constraint of the bridge pier. I'm just a signalling guy, not a track guy, so it's entirely possible that my nitpicking is unfounded.
cplchanb
Senior Member
Well if they want to have a smooth rer service they're going to need to clean up their lines, including these switches
L
ARG1
Senior Member
Well technically RER won't be heading out this far - Its terminating at Burlington LSW.
crs1026
Superstar
The reverse (curved) side of the switch has a fairly tight curvature. At least as the picture shows it looking quite tight. The tighter the curvature, the slower the speed limit for trains running through that side of the switch.
One would expect that this particular switch would be a higher speed, because the slower the turnout, the timing of the schedule will be longer and the lower the capacity of the line. Given that it’s right at the end of rhe platform, trains won’t be travelling all that fast anyways - but if the switch is the limiting factor, that’s not a good design decision.
It may just be the perspective of the photo, or there may be a good reason for it - sometimes there just isn’t room for a faster (and longer) turnout…. But with ML, one can never be sure. It’s an odd place to be pinching pennies.
- Paul
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tsm1072
Active Member
Isn't this on a CN line? I wonder if CN didn't want to create the space for the longer switch and ML wanted to get something done rather than spend more time and money for the perfect solution.
crs1026
Superstar
There would have been plenty of design work and data exchanged before ML signed off on the purchase req.
Given that ML is paying I don’t believe CN would have put any obstacles in ML’s way. There may have been an engineering constraint. Looking at Google Earth, there seems to be ample linear room for a longer switch, although perhaps the property line jogs awkwardly and ML would have needed to acquire a sliver of land to get the necessary width. Or there is something buried that would have had to be moved.
The track speed west of Aldershot is not particularly high, due to the signalling and switch configuration at Bayview Jct - and the existing track and signals west of Aldershot may have been seen as a constraint. Certainly GO trains are able to enter a station at a speed greater than 25 mph and still stop safely…. so in a perfect world one would want the crossover and signals not to force a lower speed on approach.
- Paul
smallspy
Senior Member
Unfortunately, none of my contacts know anything about this project, so until we see the actual finished track diagrams we're all going to be guessing. (Unless someone wants to trespass and measure the frog. I wouldn't recommend that.)
Even though it is located close to the platform, a higher-speed switch would be beneficial for train scheduling and timing. If permitted, a GO train entering a station does so at 35-to-40mph, and upon leaving the tail end is almost at 35mph - having slower switches will prevent those speeds from being achieved until the train is clear of that trackwork.
For the record, the speed limits of the various switches in CN usage are fairly variable, in the sense if they are used back-to-back (to form a crossover) they are allowed a certain speed:
#20 - 45mph
#16 - 30mph
#12 - 15mph
But if those same switches are used in a manner that doesn't involve an out-and-back movement such as a crossover, they can be rated for 10mph higher than those speeds.
(There are also smaller switches used, but they are virtually never used on mainline trackage - only in yards and to service industries.)
Dan
crs1026
Superstar
^One additional bit of trivia - while adding this one switch may seem like a small task, the changes to the signalling that are involved are pretty significant.
The signalling system has to give advance warning of the routing potentially several signals back from the location. In this case, there are dozens of possible routings through the various junctions (especially through Hamilton Jct- Bayview - Snake - Aldershot). That includes not only single-train scenarios where a train is lined all the way through the route (in which case the train will encounter mostly “clear”ish indications) but partial-clear scenarios where a more restrictive signals must be displayed - if for instance there is another train further ahead, or if the route has only been cleared through one or two sections ahead, the progression is different.
Each possible routing must be analysed and the correct progression of signal indications must be evaluated and engineered for that eventuality. Then, as part of the cut-in of the switch, the various interlocking plants have to be modified to ensure that the correct signal indication is displayed at that location for each eventuality. This may involve software changes or in some cases physical changes to the equipment in the field.
And then, each and every routing and permutation has to be field tested and verified before the cut-in is signed off.
Whenever anything is changed in this particular location, (as for instance happened when Hamilton Jct was rebuilt for West Harbour) that modification and testing can be a huge pile of work which has to be performed without halting operations.
The point being that this one switch can have expensive knock-on implications for signalling all the way from Burlington to West Harbour.
I’m just speculating, but it wouldn’t surprise me to learn that someone realised that the whole project could be greatly simplified if the signalling system didn’t have to anticipate a higher speed indication at this new switch. Or that some permutation of signal indications through some routings couldn’t be accommodated.
Just a conspiracy theory.
- Paul
The signalling system has to give advance warning of the routing potentially several signals back from the location. In this case, there are dozens of possible routings through the various junctions (especially through Hamilton Jct- Bayview - Snake - Aldershot). That includes not only single-train scenarios where a train is lined all the way through the route (in which case the train will encounter mostly “clear”ish indications) but partial-clear scenarios where a more restrictive signals must be displayed - if for instance there is another train further ahead, or if the route has only been cleared through one or two sections ahead, the progression is different.
Each possible routing must be analysed and the correct progression of signal indications must be evaluated and engineered for that eventuality. Then, as part of the cut-in of the switch, the various interlocking plants have to be modified to ensure that the correct signal indication is displayed at that location for each eventuality. This may involve software changes or in some cases physical changes to the equipment in the field.
And then, each and every routing and permutation has to be field tested and verified before the cut-in is signed off.
Whenever anything is changed in this particular location, (as for instance happened when Hamilton Jct was rebuilt for West Harbour) that modification and testing can be a huge pile of work which has to be performed without halting operations.
The point being that this one switch can have expensive knock-on implications for signalling all the way from Burlington to West Harbour.
I’m just speculating, but it wouldn’t surprise me to learn that someone realised that the whole project could be greatly simplified if the signalling system didn’t have to anticipate a higher speed indication at this new switch. Or that some permutation of signal indications through some routings couldn’t be accommodated.
Just a conspiracy theory.
- Paul
Allandale25
Senior Member
Do the numbers 20, 16, 12 have any meaning? It would be easier to remember if the switches were named after their speed (i.e. a number 45 is for 45mph).
jamincan
Active Member
It is a measure of the divergence - "This divergence is measured as the number of units of length for a single unit of separation. In North America this is generally referred to as a switch's "number". For example, on a "number 12" switch, the rails are one unit apart at a distance of twelve units from the center of the frog." https://en.wikipedia.org/wiki/Railroad_switch#Classification
Allandale25
Senior Member
^ Thanks!
smallspy
Senior Member
Beat me to it - thanks.
As a further addendum to this, this system is predominantly a North American thing. Our switches are generally straight through the frog. In Europe, and especially in France and Germany, they use curves and spirals through the whole length of their switches, and generally they allow higher speeds through them despite being the same approximate "size".
As well, these are by no means the only NA sized switches available, and nor are they only operated at that speed. Several of the US roads use very similar geometries in their switches but allow slightly higher (and sometimes slightly lower) speeds than CN/VIA/Metrolinx do. Amtrak has a larger standardized design that allows for 80mph operation on the diverging route when used in a crossover.
Absolutely, positively, not the case.
The signal system through there was thoroughly redone as part of the triple-tracking 15 years ago, and all of the various systems in there are all quite modern. (In fact, didn't they recently upgrade to fibre further west recently?) Changing them for track remodellings like this is not a big deal for them anymore.
Dan
crs1026
Superstar
One would think so, but there was that set of crossovers at Bayview that were installed and tested, failed the tests and then sat idle forever - reportedly because the software wasn’t right.
The modern stuff is eminently flexible, but it’s common practice to not install 3-colour signal heads unless the design needs them…. so physical mods sometimes have to happen before the changes can be made, to provideall the aspects required.. I don’t know that that’s the situation here.
Like I said, just a conspiracy theory.
- Paul