Request ID: FOI-2025-2223 Date published: 25 November 2022
You asked
Dear TfL
I notice the official rolling stock information sheets categorised Northern Line rolling stock as having 1995 trains with "rubber chevron primary and secondary suspension" (see 4th ed. Tfl Rolling Stock Information Sheets).
Various third party sources note the Adtranz bogies for 1995 stock have air suspension.
A bogie design compendium document from SKF mentions that in fact, AdTranz bogies can have a dual design i.e. rubber and air.
Please would you be kind enough to clarify what the current Northern Line trains have fitted for suspension? Is it just rubber coils or chevrons or is there also an air suspension?
Can you please comment on whether the air suspension is a sealed unit (if fitted) and provide information on the routine maintenance required e.g. does air need adjustment or refilling as a regular service item, and at what frequency?
Can you also comment on whether air suspension (if fitted) is under driver or automated control and should/can be varied in line with track conditions along the route.
Please can you also provide information on the maintenance regime for the rubber suspension and an indication of how often these elements should normally be inspected, what interval is there between replacement/what is the specified service lifetime?
Can you also provide an indication of whether trains are being inspected within normal operational routines, and if so, how often.
What is the condition of Northern Line train suspension?
How many trains have exceeded their specified service interval while below expected performance i.e. remain overdue for servicing/repair of their suspension?
Has any engineering assessment been carried out of the ability of the train suspensions and braking to support ATO over the long term, without excessive noise and vibration arising, or how to mitigate if it arises?
We answered
TfL Ref: 2025-2223
Thank you for your request received by Transport for London (TfL) on 15 November 2022 asking for information about the London Underground Rolling Stock Data Sheets on Northern Line trains. Your request has been considered in accordance with the requirements of the Freedom of Information Act and our information access policy. I can confirm that we hold the information you require. You asked:
Please would you be kind enough to clarify what the current Northern Line trains have fitted for suspension? Is it just rubber coils or chevrons or is there also an air suspension?
We can advise that there is an error in the Rolling Stock Data Sheets; these trains are fitted with rubber “air bag” secondary suspension.
Can you please comment on whether the air suspension is a sealed unit (if fitted) and provide information on the routine maintenance required e.g. does air need adjustment or refilling as a regular service item, and at what frequency?
The air suspension is “active,” It responds to the loading in the carriage and air is added or removed by the pneumatic system at all times while the train is in operation.
Can you also comment on whether air suspension (if fitted) is under driver or automated control and should/can be varied in line with track conditions along the route. T
The suspension is “automatically” controlled by the train. The Train Operator will receive a warning message if an air bag is deflated due to some form of system fault.
Please can you also provide information on the maintenance regime for the rubber suspension and an indication of how often these elements should normally be inspected, what interval is there between replacement/what is the specified service lifetime?
Can you also provide an indication of whether trains are being inspected within normal operational routines, and if so, how often.
Trains have a general visual inspection every few weeks (generally dependant on service mileage run), to detect any gross defects. Secondary suspension is maintained as part of heavy overhaul, which is nominally every nine years. Change outs at this time will be inspection/condition driven.
What is the condition of Northern Line train suspension?
Suspension is deemed to be in good condition. The train is within its expected design life and has been subjected to the prescribed maintenance regime to keep it in a serviceable condition.
How many trains have exceeded their specified service interval while below expected performance i.e. remain overdue for servicing/repair of their suspension?
All trains are within their required maintenance interval.
Has any engineering assessment been carried out of the ability of the train suspensions and braking to support ATO over the long term, without excessive noise and vibration arising, or how to mitigate if it arises?
As the Automatic Train Operation performance of the train is within the original design parameters of the train, no further assessment has been undertaken. We have now operated for a number of years in Automatic Train Operation mode without any concerns around suspension or braking performance. Our London Underground engineers work with manufacturer and maintenance company Alstom, in the event of issues arising and identify suitable mitigations and fixes accordingly.
If this is not the information you are looking for, or if you are unable to access it for any reason, please do not hesitate to contact me.
Please see the attached information sheet for details of your right to appeal as well as information on copyright and what to do if you would like to re-use any of the information we have disclosed.
Yours sincerely
Jasmine Howard FOI Case Officer FOI Case Management Team General Counsel Transport for London
