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Post by vjaska on Apr 27, 2015 23:36:59 GMT
You also find the difference in track quality on different parts of the Jubilee Line. The whole 1990s JLE section with continuous welded rail is very smooth, but as soon as you reach the junction with the 1970s section at Green Park you hit the old jointed rail and you get bounced all over the place. Maybe the track in the section you mentioned is just old and needs replacing? All track on the Victoria Line was replaced as part of the upgrade project. It's why we had early finishes 5 nights a week for two years before the new trains could be deployed. Generally the Vic Line track is well looked after because a few years ago they didn't look after it and the service was a complete and utter shambles for months. Once bitten, twice shy and all that. Given that it's normally pretty smooth I was shocked that the ride was as rough as it was. The Brixton crossing and the track just before when heading into Brixton can be a bit rough - on a different subject, is the Brixton crossing still the busiest of it's type in the world?
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Post by John tuthill on Apr 28, 2015 8:04:06 GMT
All track on the Victoria Line was replaced as part of the upgrade project. It's why we had early finishes 5 nights a week for two years before the new trains could be deployed. Generally the Vic Line track is well looked after because a few years ago they didn't look after it and the service was a complete and utter shambles for months. Once bitten, twice shy and all that. Given that it's normally pretty smooth I was shocked that the ride was as rough as it was. The Brixton crossing and the track just before when heading into Brixton can be a bit rough - on a different subject, is the Brixton crossing still the busiest of it's type in the world? How many trains use it compared to the Bakerloo at the Elephant & Castle?
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Post by snoggle on Apr 28, 2015 9:41:32 GMT
The Brixton crossing and the track just before when heading into Brixton can be a bit rough - on a different subject, is the Brixton crossing still the busiest of it's type in the world? How many trains use it compared to the Bakerloo at the Elephant & Castle? I think the Vic Line is now up to 33 or 34 tph in the peaks so 66-68 movements in an hour at Brixton as there are no short turns at Victoria. The Bakerloo is 22 tph at the height of the peak (both from the relevant WTT). Amazingly the *daily* off peak is a train every 2.25 mins out of Brixton - incredible really if you compare back to the mid 1980s when trains were nowhere near that frequent off peak. Whether it's the busiest in the world I really can't say. I suspect there may be other systems that run on similar very high headways. Money has been approved to increase to 36tph on the Victoria Line. This is why the Walthamstow crossover is being replaced this Summer - it'll allow faster run in / run out speeds.
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Post by John tuthill on Apr 28, 2015 13:10:22 GMT
How many trains use it compared to the Bakerloo at the Elephant & Castle? I think the Vic Line is now up to 33 or 34 tph in the peaks so 66-68 movements in an hour at Brixton as there are no short turns at Victoria. The Bakerloo is 22 tph at the height of the peak (both from the relevant WTT). Amazingly the *daily* off peak is a train every 2.25 mins out of Brixton - incredible really if you compare back to the mid 1980s when trains were nowhere near that frequent off peak. Whether it's the busiest in the world I really can't say. I suspect there may be other systems that run on similar very high headways. Money has been approved to increase to 36tph on the Victoria Line. This is why the Walthamstow crossover is being replaced this Summer - it'll allow faster run in / run out speeds. Thanks for the info
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Post by jrussa on Apr 28, 2015 23:34:02 GMT
They may well have the capability but it's possible the current timetable doesn't require it to be exploited. Not a lot of point of travelling at rocket like speeds only to have to jam the brakes on 1 minute later. You'll just throw people all over the place. Last time I used the Vic I noticed the track quality between SS and F Park s/b was diabolical - the train was bouncing all over the place. It's the same with different trains so it's definitely the track not a unit with "flats". Shows the track is getting a bit of a hammering with the more intensive service levels. You also find the difference in track quality on different parts of the Jubilee Line. The whole 1990s JLE section with continuous welded rail is very smooth, but as soon as you reach the junction with the 1970s section at Green Park you hit the old jointed rail and you get bounced all over the place. Maybe the track in the section you mentioned is just old and needs replacing? Absolutely! I was on the jubilee line on Monday afternoon coming from the airport (been to Jamaica) and I thoroughly enjoyed the Jubilee Line between Green Park and Bond Street. It felt as if the train was skiing at 200mph and swerving obstacles
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Post by M1104 on Apr 29, 2015 0:24:24 GMT
You also find the difference in track quality on different parts of the Jubilee Line. The whole 1990s JLE section with continuous welded rail is very smooth, but as soon as you reach the junction with the 1970s section at Green Park you hit the old jointed rail and you get bounced all over the place. Maybe the track in the section you mentioned is just old and needs replacing? Absolutely! I was on the jubilee line on Monday afternoon coming from the airport (been to Jamaica) and I thoroughly enjoyed the Jubilee Line between Green Park and Bond Street. It felt as if the train was skiing at 200mph and swerving obstacles My cousin from New York rode the old and new section jubilee line last year and his exact words were, "y'all trains are like rollercoasters!"
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Post by Hassaan on Apr 29, 2015 1:32:28 GMT
You also find the difference in track quality on different parts of the Jubilee Line. The whole 1990s JLE section with continuous welded rail is very smooth, but as soon as you reach the junction with the 1970s section at Green Park you hit the old jointed rail and you get bounced all over the place. Maybe the track in the section you mentioned is just old and needs replacing? All track on the Victoria Line was replaced as part of the upgrade project. It's why we had early finishes 5 nights a week for two years before the new trains could be deployed. Generally the Vic Line track is well looked after because a few years ago they didn't look after it and the service was a complete and utter shambles for months. Once bitten, twice shy and all that. Given that it's normally pretty smooth I was shocked that the ride was as rough as it was. Thanks for the correction. Did see the old style bullhead rail in one of the platforms recently, one of either King's Cross, Euston, Green Park, or Victoria, which is why I thought some track hadn't been replaced.
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Post by allentc on May 13, 2015 12:32:57 GMT
The answers have now been published: Andrew Dismore A constituent has complained about ride quality, to do with the uncomfortable and never-ending changes between acceleration and braking, rather than track alignment or train suspensions. He asks are trains attempting to run at a computerised predefined speed at each instant of travel? For a typical section of track away from stations, how wide, in km/hour, is the allowable speed range, such that above it the brakes are applied, and below it the accelerator? In this middle range, do the trains just coast or at least are on purely nominal base power?
The Mayor The new signalling system on the Northern line is now allowing London Underground to deliver a much needed increase in capacity and train frequencies - especially during the busiest times. Since December 2014, there has been a 20 per cent increase in capacity through central London on the Northern line and increased train frequencies of up to 24 trains per hour on the Charing Cross branch and up to 26 trains per hour on the Bank branch.
In order to accommodate the increasing demand along the line, these frequencies will continue to increase incrementally in the coming years.
There is not one predefined speed at which trains will travel on the new signalling system. Trains accelerate as they leave the platform, coast once they reach their target speed, and brake as they enter a platform. The upper or lower limit of the period the train will coast at its target speed - up to 80 km per hour - is not fixed. It is also dependent on a number of factors, such as gradient. All of the system's actions are monitored, regulated and fit within an industry standard rate.
When the new signalling was first introduced, minor adjustments were made to the smoothness of the ride in order to achieve a balance of ride experience whilst achieving desired levels of trains per hour. If further adjustments are made, it would mean reducing train speed, thereby affecting the timetable.
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Andrew Dismore In determining what acceleration or deceleration to apply to a train, does the new system have knowledge of how full the train is? Can the 1995 stock? Can the new sub-surface stock? Does the weight of any Underground train dramatically change the calculation necessary for typical desired braking and acceleration? Is this something the Northern Line system is unable to take into account?
The Mayor The new signalling system does not have knowledge of the weight of the train (hence how full it is), therefore the weight of the train is not taken into account when the signalling system calculates what acceleration or deceleration to apply to a train.
The weight of an Underground train does not change the calculation for desired braking and acceleration.
In a process separate from the new signalling system itself, the 1995 stock's braking system does have knowledge of the weight of the train and applies differing levels of braking force. This is also the approach adopted by the new sub-surface stock.
----- Andrew Dismore Is the Northern Line computerised drive system able to anticipate the needs of the next section of track, or is acceleration and deceleration purely calculated on the current instant of time and its 'actual against desired' speeds? Is this the missing factor, that train drivers unconsciously provided, and that your new system cannot?
Do you accept the ride is unacceptably jerky?
The Mayor The new Transmission Based Train Control (TBTC) signalling system scans ahead of the train and issues a target point to which the train drives, calculating the required speed as it goes. Drivers would have done a similar action when driving to the old colour light signalling system where they were effectively given a permitted destination to drive to, and then would have driven up to line speed to that point. Trains are now able to utilise their full performance potential and are able to accelerate at nearly twice the rate (1.3m/s/s). Line speed limits in many areas have been uplifted and the TBTC system can cope with more frequent changes in speed limit to maximum performance.
The trains are operating within the Jerk Limits specified within London Underground's standards. TfL will continue to monitor performance on the line and make adjustments as required.
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Andrew Dismore Do your engineers hold speed and acceleration data for the same sections of track, from earlier driver-operated and current automatic operation? Have they ever made a comparison? With what result? If the former quality of ride was deemed subjectively 'acceptable' by passengers, how would you describe the current situation?
The Mayor Yes, London Underground's engineers have records of actual train 'Run Profiles' from before and after the re-signalling. As mentioned in my response to 2015/0948, the train performance has changed considerably. Any comparison will show that the trains are accelerating substantially faster, are running at higher speeds, are following the permitted line speeds more closely, and have a reduced inter-station run times enabling a faster and more frequent service. The current ride quality is in line with the other modern signalling and train systems deployed on the Underground delivering a similar level of performance to the upgraded Northern line.
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