hawc
Senior Member
What's this 'Science Centre' that you speak of?
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What's this 'Science Centre' that you speak of?
Bojaxs
Senior Member
But doesn't line 1 & 2 both being completely grade separated factor into this?
Do the red lights on Line 5 have an impact on train spacing?
Towered
Superstar
Rumour has it that the roof has not actually collapsed from snow for the past few years as was initially hyped as imminent...
T3G
Senior Member
No, because in this analogy, it matters not whether the line is grade separated or not - you are still slowing way down from the previous track speed.
Hell, you don't need to even look at slow zones - in between Bloor-Yonge and Eglinton West, Line 1 naturally slows way down due to shorter distances between stations, and the presence of many curves and timers. But you don't see a traffic jam outside those 2 stations going southbound, because, if the line is running according to plan, *every single train* starts equally fast and then slows down to the same rate of speed.
Bottom line is this: as long as all trains are operating under the same conditions, are all subject to the same speed limits and operating rules, there is zero reason why bunching should occur.
Bunching happens due to random acts of chance that develop during the day: passengers that take their time getting on, disruptions such as door holders, alarms, minor mechanical problems, an inability of terminals to process the correct amount of trains in one go (this is why there is routinely bunching outside of Finch and Kennedy during the rush hours), and on the surface network, the irregularity of mixed traffic, and operators playing games (i.e. they cling to their leader's ass, so that they don't have to pick anyone up and can have an easy trip). Having a line with mixed top speeds is not at all a factor.
Bojaxs
Senior Member
Why did you completely gloss over the second part of my post?
Will they time every train to hit the same red light at the exact same time?
We probably won't see bunching, but I suspect we'll see trains extending dwell times at stations in order to maintain spacing.
So I suspect the red lights at the surface portion will have a "trickle down" effect into the underground portion. I'm referring to eastbound trains.
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A 6264
Active Member
That was the mine cart exhibit. The first time I saw it on a school trip, I thought they were going to let us ride in the carts. Disappointment!
T3G
Senior Member
Because the second part of your post is already covered by the post I made.
It is physically impossible to ensure every train hits the same red light at the exact same time, in the same way it's physically impossible for every train on lines 1 and 2 to have the exact same dwell time at every station. But being separate from traffic removes a great deal of variability away, and, provided that the TTC doesn't do anything stupid to intentionally kneecap their own operation (which, I will grant you, is not out of the question), there is nothing in the inherent physical design of the line that will cause any of the problems you are concerned about.
What is the point of having trains extending dwell times at underground stations, if they should also hit red lights on the surface section? The 5 is supposed to run much more frequently than the 6 is, so there's no concern about maintaining a set schedule, they will most likely utilize headway based frequencies instead as they do on lines 1 and 2. No one's going to freak out if a train here and there is a minute early or a minute late, because they will run frequently enough for it not to matter.
Bojaxs
Senior Member
How do you know it's going to hit the same red lights as the train before it?
I guess what I want to know is will the surface portion of the line impact speeds in the underground portion of the line? Particularly heading eastbound? I mean, they can't allow the underground portion to travel too much faster than the trains in front of them on the surface portion, correct?
If you're going to construct a transit line to have both an underground portion and surface level portion, than it seems something like TPS for the surface portion is a necessity. Help keep things flowing.
A 6264
Active Member
See my reply on the other thread, where I suggested considering a toy marble and track. If the marbles run 15 seconds apart from each other, they do so on both fast and slow sections. If the slow section runs even slower, it doesn't change anything.
I do understand your concern. You probably see buses coming through in little bundles of 3 or 4 at once, after waiting 20 minutes for one, and wonder what causes the "bunching". In theory it shouldn't happen; in practice it does. You're trying to resolve the issue by re-inventing the theory and treating irrelevant factors as relevant. Sort of like saying rocket ships can't work in space, because their rocket exhaust has nothing to push against -- which is something people have actually said.
A 6264
Active Member
No. The surface portion can run at a crawl, and the underground portion can still run at 200 KPH.
(Okay, they can't, but you know what I mean.)
Bojaxs
Senior Member
Yes, and in that post you mention that the marbles DO in fact bunch up once in the slow section.
The goal shouldn't be to bring down the speed of the trains in the underground portion to accommodate the surface portion of the line. The surface portion of the line needs to have their speeds brought up to allow for faster trains in the underground portion.
A 6264
Active Member
Maybe you and I are using "bunching up" in different ways. I was trying to say the marbles are closer together in any slow section, which is maybe what you meant by bunching up. If, by "bunching up", you mean coming to a stop, then no, that's not what I was saying. And most important (because it's the point you're trying to make), marbles being slow in some parts in the track, have ZERO effect on how fast they move in the fast parts.
eglinton1661
New Member
1. Red lights and other sources of interference aside, it is possible to have trains run faster in the underground portion and slower in the overground portion and maintain a constant frequency across the entire line.
2. In the above case, trains would be physically farther apart in distance in the underground portion, and physically closer in distance in the overground portion. You might call this "bunching up." But because the trains are travelling slower above ground, they still arrive at the same frequency as they would under ground.
3. External interference (red lights, variable dwell times) do mess up the frequency as some trains will travel across the line faster than others. When this is severe enough, it causes "bunching," as in: several trains arriving quickly after each other, following by a long period with no trains. In that case, Laird Station is designed to allow short turns, which is intended to mitigate the problem. See:
Obviously nobody likes short turns and I'm not advocating for them, but this is an option available in the system.
2. In the above case, trains would be physically farther apart in distance in the underground portion, and physically closer in distance in the overground portion. You might call this "bunching up." But because the trains are travelling slower above ground, they still arrive at the same frequency as they would under ground.
3. External interference (red lights, variable dwell times) do mess up the frequency as some trains will travel across the line faster than others. When this is severe enough, it causes "bunching," as in: several trains arriving quickly after each other, following by a long period with no trains. In that case, Laird Station is designed to allow short turns, which is intended to mitigate the problem. See:
Obviously nobody likes short turns and I'm not advocating for them, but this is an option available in the system.
T3G
Senior Member
They might not all hit every single one, but it makes little difference if a train hits, say, the light at Birchmount vs. Victoria Park, for example. It all averages out, if the experience on Finch West is anything to go by - the fact that the light might turn in time for one train at one intersection doesn't mean it doesn't then stop and hit most other red lights on the journey.
They can do exactly that.
Again, remember - it's not as though one train will be subject to traffic lights, while the others won't. It will be all of them. If one train waits at a bunch of traffic lights, so will the others. There is no danger of them catching up, unless the first train in front encounters a mechanical problem or a breakdown or a signal issue or passengers taking their sweet time boarding.
You're thinking about this too much. The lack of TSP is a problem, but there is no reason why that should result in bunching. Bunching is caused by a factors you encounter on the subway, too. I exit the GO train at the same spot and usually make my way to the 1 platform at Union before the rest of the passengers. Sometimes there's a train 1 minute away, and therefore it's lightly loaded on leaving Union and has only had a dwell time of around 20 seconds. Sometimes there's a train 4-5 minutes away, and we have a crushload that takes longer to load, and it can take 40-60 seconds for the train to be able to leave. And if there's a train right behind that one, it will follow its leader most of the way up the line, because it has, again, a minimal load in comparison to the one in front of it. This is one of those random acts of chance I referred to.
Voltz
Senior Member
It's been explained several times how the concerns of bunching or slowing down in the underground section are unwarranted. If you still don't want to believe it then don't.
It's simple, the cars just get closer together on the slower section but maintain the same headway. Once they get back to the faster section they get farther apart but speed up.