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Old October 14th, 2015, 04:48 PM   #10181
flankerjun
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Old October 16th, 2015, 01:21 AM   #10182
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Quote:
Originally Posted by chornedsnorkack View Post
Increasing speed does not increase line capacity/supply at all. It does, as pointed out, increase demand. If demand already exceeds supply, increasing speed will make a bad situation worse.
Speed is major part of the formula that determines a line's capacity so speed increase generally means increased capacity.

To simply put it, for a given time you can run more trains with higher speed so capacity increases.
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Old October 16th, 2015, 09:35 AM   #10183
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Quote:
Originally Posted by foxmulder View Post
Speed is major part of the formula that determines a line's capacity
Where?
Quote:
Originally Posted by foxmulder View Post
so speed increase generally means increased capacity.

To simply put it, for a given time you can run more trains with higher speed so capacity increases.
Do you mean increase of speed directly decreases headways?
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Old October 16th, 2015, 07:13 PM   #10184
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Mathematics here is pretty simple - in theory speed has no impact on the line capacity. What does have a huge impact is trains with different speeds.
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Old October 16th, 2015, 07:40 PM   #10185
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No, it's not that easy. With higher speeds, braking distance increases quadratically whereas the time that a section remains occupied only decreases linearly, so that the capacity is decreased.
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Old October 17th, 2015, 12:57 AM   #10186
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Capacity decreases with speed... LOL
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Old October 17th, 2015, 02:01 AM   #10187
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Eh, yes?

To put it simple: with subways, it is not much of a problem to run with 90s headways. But a HSR train travelling at 350 km/h already needs more than 90 seconds to come to a full stop, plus the inefficiency of fixed-block train detection. Thus, 90s headways are absolutely not feasible in HSR traffic. (Except if one were to use moving-block train detection in combination with relative rather than absolute braking distance calculation in the interlocking, but all of that is still in the future, AFAIK.)

But on the other hand, higher speed does mean that you can transport more people with the same amount of vehicles and staff.
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Old October 17th, 2015, 02:57 AM   #10188
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the higher speed means more trains in one hour,so it increases the,capacity
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Old October 17th, 2015, 05:24 AM   #10189
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those brown accent trains look better then the blue
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Old October 17th, 2015, 06:11 AM   #10190
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Quote:
Originally Posted by flankerjun View Post
the higher speed means more trains in one hour,so it increases the,capacity
Why? You can dispatch similar amount of trains regardless of their speed. It may have some affect on capacity but overall it's quite minimal. It's not a major factor.

A major factor for capacity would be train size (how many passengers can fit in one train), signalling, boarding procedures etc. Speed in itself doesn't play much of a role.
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Old October 17th, 2015, 08:20 AM   #10191
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For a long line such as Beijing - Shanghai, a marginal increase in speed (50 km/h) can create a huge time savings, which means the train can be turned around for more trips. That's the capacity increase.

With huge cities along that line, and Beijing and Shanghai being large themselves, I see a need to build duplicate lines, not just to create redundancy in case the other line goes down, but also to push the frequencies up. You can speed up the existing trains but the capacity that can be squeezed in won't be too significant.
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Old October 17th, 2015, 09:25 AM   #10192
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Quote:
Originally Posted by hkskyline View Post
For a long line such as Beijing - Shanghai, a marginal increase in speed (50 km/h) can create a huge time savings, which means the train can be turned around for more trips. That's the capacity increase.
Only if there is a shortage of trains.
If, for example, Beijing-Shanghai takes 5 hours and there are 12 trains per hour at 5 minute headways, then there are 60 trains on the tracks between Beijing and Shanghai at any time.
Now suppose that these 60 trainsets are all that are available. Then if the line is sped up so that the trip now takes 4 hours, these 60 trainsets might start to travel at 15 per hour, 4 minute headways.
But this does not work if the line is full. Then the trains cannot travel at 4 minute headways because they would get in the way of each other and collide. Assuming 5 minute headways are still possible, the line capacity remains unchanged at 12 trains per hour (as pointed out, it might decrease instead) and only 48 trains can occupy the line at a time. The remaining 12 then become surplus to requirements and must be parked at depot, or sold off and their crews fired, or reassigned to other lines which are not yet full.

Is Beijing-Shanghai line full, or not?
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Old October 17th, 2015, 10:10 AM   #10193
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Quote:
Originally Posted by Pansori View Post
Why? You can dispatch similar amount of trains regardless of their speed. It may have some affect on capacity but overall it's quite minimal. It's not a major factor.

A major factor for capacity would be train size (how many passengers can fit in one train), signalling, boarding procedures etc. Speed in itself doesn't play much of a role.
That is true unless as mentioned above we go to extreme densities and need to take into account braking distances. However allowing just a single train capable of only 200 km/h on that line every hour would drastically reduce capacity (for simplicity assume no passing loops). So in that sense a speed does have an impact on capacity.

In the real world capacity of high speed line is also higher because you can use daytime more efficiently. For example if it takes 1 h to cover the distance between city A and B the last train might be at 11 pm there as if it takes 3 h the last one might be at 9 pm since is not that desirable to arrive somewhere at 3 am.
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Old October 17th, 2015, 10:57 AM   #10194
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Quote:
Originally Posted by Sunfuns View Post
In the real world capacity of high speed line is also higher because you can use daytime more efficiently. For example if it takes 1 h to cover the distance between city A and B the last train might be at 11 pm there as if it takes 3 h the last one might be at 9 pm since is not that desirable to arrive somewhere at 3 am.
Although slow speed trains do.
On Beijing-Shanghai, there are 4 trains that are not G.
Of these, D313 arrives at Nanjing 4:54 and Changzhou 5:58. Note that D trains Beijing-Shanghai run on slow speed railway.
T109 arrives at Xuzhou 3:01.
1461 arrives at Bengbu 0:49, Chuzhou North 2:14, Nanjing 3:01, Zhenjiang 3:48, Danyang 4:10, Changzhou 4:43, Wuxi 5:14.

How should overnight high speed trains be scheduled?
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Old October 17th, 2015, 03:28 PM   #10195
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Quote:
Originally Posted by chornedsnorkack View Post
Only if there is a shortage of trains.
If, for example, Beijing-Shanghai takes 5 hours and there are 12 trains per hour at 5 minute headways, then there are 60 trains on the tracks between Beijing and Shanghai at any time.
Now suppose that these 60 trainsets are all that are available. Then if the line is sped up so that the trip now takes 4 hours, these 60 trainsets might start to travel at 15 per hour, 4 minute headways.
But this does not work if the line is full. Then the trains cannot travel at 4 minute headways because they would get in the way of each other and collide. Assuming 5 minute headways are still possible, the line capacity remains unchanged at 12 trains per hour (as pointed out, it might decrease instead) and only 48 trains can occupy the line at a time. The remaining 12 then become surplus to requirements and must be parked at depot, or sold off and their crews fired, or reassigned to other lines which are not yet full.

Is Beijing-Shanghai line full, or not?
You can easily search the schedule and see headways are nowhere near 5 minutes. Rolling stock is not an issue. There is a huge domestic manufacturer than can churn them out.
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Old October 17th, 2015, 05:25 PM   #10196
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Some pictures of Jilin-Hunchun HSR,copyright @铁路小亨









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Old October 17th, 2015, 05:27 PM   #10197
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Damn those are beautiful views. I want to get there myself and take some photos
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Old October 17th, 2015, 07:07 PM   #10198
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Some impressions from a short ride between Shenzhen North and Guangzhou South railway station.

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Old October 17th, 2015, 08:40 PM   #10199
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Quote:
Originally Posted by Sunfuns View Post
That is true unless as mentioned above we go to extreme densities and need to take into account braking distances. However allowing just a single train capable of only 200 km/h on that line every hour would drastically reduce capacity (for simplicity assume no passing loops).
Thatīs the description of Jilin-Hunchun high speed railway. Speed 200 km/h, 10 trains daily departing from 7:12 to 18:46.
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Old October 17th, 2015, 09:55 PM   #10200
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Quote:
Originally Posted by chornedsnorkack View Post
Thatīs the description of Jilin-Hunchun high speed railway. Speed 200 km/h, 10 trains daily departing from 7:12 to 18:46.
Are there some trains doing 300 km/h and some others 200 km/h? If not then your example is not a good one.
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