Dear Stakeholder,
I am writing to you as someone who has previously contacted London Overground about the disruption experienced from the noise of trains passing through curves, which is commonly known as curving noise.
I hope to be able to keep all stakeholders updated with regular information about the issue. This initial update is to explain the background to curving noise and to detail the steps TfL is taking to alleviate the issue. In future updates I hope to be able to explain the actions taken.
INTRODUCTION
TfL is aware that curving noise has given rise to a number of complaints since the London Overground service commenced. TfL is taking this matter very seriously and is in the process of trying to find a solution. This note is to inform residents about the causes of curving noise and to provide an update on what steps TfL is implementing to address this issue.
CAUSES OF CURVING NOISE
Curving noise is not a straightforward issue. Whilst it is caused by the rubbing/slipping of the train’s wheel on the rail as it moves through a curve, the actual elements rubbing/slipping can vary on different curves. To be able to address the problem, it is first necessary to understand which elements are involved.
There are three main causes of curving noise.
1. Wheel squeal - this results when the part of the wheel which rests on the rail slips small amounts repeatedly across the top of the rail
2. Flanging – this is when the wheel flange (the overhung side of wheel which prevents the wheel from coming off the rail) rubs against the side of the rail.
3. Flange contact - where the back of the wheel flange makes contact with an additional rail (the check rail) which helps ensure that the train does not de-rail on a corner.
Curving noise most commonly occurs on sharp curves, places where tracks crossover or in locations where there is ineffective lubrication of rails on curves. However, other factors that can influence the occurrence of curving noise include:
· undulating (up and down) track
· rough wheel and/or rail surfaces
· out of shape wheels
· weather conditions (particularly the presence / absence of rain or the level of humidity)
· variations in train speed.
CONSIDERATIONS IN SOLUTIONS – SAFETY, PERFORMANCE, WEAR, NOISE
The primary method of controlling curving noise is to control the amount of friction between the wheel and the running rail. On the East London Line, a number of flange lubricators have been installed to lessen the friction between the wheel flange and the rail – thus reducing flanging noise. In addition, top of rail friction modifiers have been installed to control the levels of friction on the top of the rail and thus limit the noise associated with wheel squeal.
The East London Line is believed to be the first railway in the UK to open with top of rail friction modifiers in place from opening. These units are relatively new pieces of equipment, and they do not currently have full approval to be used on National Rail network – currently they are only be used on National Rail network at selected sites under a trial approval certificate.
However, as TfL considers that top of rail friction modifiers can be effective in reducing curving noise, approval has been given to the use of these items on the East London Line on a trial basis. However, given the new nature of the equipment, there will inevitably be a period of time required to adjust the set-up such that the units work to their maximum effectiveness.
As you will appreciate, the operations on a railway are safety critical, and all activities and adjustments need to be undertaken in a controlled manner such that no need new safety risks are introduced.
As such, the use of lubricators and friction modifiers on the railway needs to be carefully controlled as over application of these materials can result in the following problems:
· increased stopping distances due to the reduced braking efficiency
· potential collision risk caused by a train overrunning the signal and colliding with another train or hitting the buffers
· the generation of wheel and rail defects
· delays caused by the train overrunning the station and the doors not opening
· the potential fire hazard and environmental impact of excessive grease and oil spatter
· potential for fatigue cracking on the rail
Given the above, a number of safety and performance issues need to be taken into account when determining the optimum solution to reduce curving noise by the use of lubrication and friction modification systems. As such, any adjustments that are made need to be made in a controlled and systematic manner. This obviously takes time. Time is also needed after any adjustments to determine whether the adjustment has been beneficial or not in reducing curving noise.
Please be assured, however, that TfL is taking all reasonable measures to solve this problem and to make any adjustments to the existing systems in a controlled and systematic manner that does not result in any unacceptable safety risks being imported into the operation of the railway.
ACTIVITIES PLANNED/ACTIONS TAKEN
TfL has undertaken visual observations and noise monitoring to identify the curves giving rise to the curving noise. Three initial priority sites have been identified to target at present (two in Lewisham and one in Hackney). These comprise:
· The ‘Back Road’ at the New Cross Gate Depot (i.e. the tracks that go beneath the flyover to the maintenance shed),
· The Flyover that carries the tracks over the New Cross Gate Depot, and
· The Holywell Curve (just north of the new Shoreditch High Street Station towards Hoxton station).
Further assessments on the Back Road are currently being undertaken to ascertain the exact cause of the noise and thus assist in determining what further can be done to mitigate it. The lessons learnt from this exercise will be used as a basis to progress solutions at other locations.
In addition, the data from the visual observations and noise monitoring is being used to develop proposals for longer term unattended monitoring systems.
TfL has also met with a number of industry experts (including acoustic experts) from London Underground, Arup and Network Rail and the University of Southampton to discuss approaches to controlling curving noise.
Currently, TfL’s maintenance team is working with the suppliers of the lubricators and top of rail friction modifiers to adjust the equipment so that it is working at its optimum.
SPECIFIC ACTIVITIES UNDERTAKEN / PLANNED
The following provides a brief summary the actions that TfL has already taken, or is in the process of undertaking, to address the curving noise issue:
· a detailed record of the exact location of each lubricator system has been established to ensure there are accurate records
· multiple visits have been made to check that the existing systems are working correctly and to make adjustments to improve their performance
· a dedicated database has been developed to capture and manage complaints about curving noise. This will assist in undertaking trend analysis etc
· Back Road at NXG Depot:
o additional maintenance has been carried out on the existing flange lubricators, and the settings have been optimised to improve the spread of lubricant around curve
o an additional lubricator has been installed on the check rail,
o specialist noise monitoring on board a moving train is to be undertaken to understand the impact of the above modifications - it is hoped the monitoring will help identify whether there is a need to relocate the existing lubricators or use top of rail friction modifiers.
· Holywell Curve/NXG Flyover:
o fixed noise monitoring kit is being specified. Once any appropriate system has been defined, this will be installed to enable easier access to data on the occurrence of wheel squeal events – thus enabling TfL to assess the effectiveness of adjustments made to the existing lubrication systems.
Whilst we appreciate the disruption can be difficult for those living and working nearby please be assured Transport for London is taking the issues seriously and working hard to alleviate the disruption caused by curving noise.
We hope to be able to keep all stakeholders regularly updated with progress via an email bulletin. If you do not wish to receive further email updates please let me know.
Regards
Julie Dixon
Head of Marketing & Communications
