beleben

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The tramway in Stephenson Place

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With its abrupt bend at the foot of a steep gradient, the Midland Metro in Birmingham’s Stephenson Place must be one of the most hazardous sections of track in Great Britain. This month has seen the posting of wardens in hi-vis at the top and bottom of the incline, apparently to try to manage pedestrian flow in the busiest times of the Christmas period.

Street warden at top of Stephenson Place, December 2016

Street warden at top of Stephenson Place, December 2016

The curve at Stephenson Place is potentially as hazardous as the one at Sandilands on Croydon Tramlink, where a derailment on 9 November of a tram travelling at excess speed resulted in deaths and serious injuries. The Croydon derailment, which received extensive press coverage, is the subject of an investigation by the Rail Accident Investigation Branch.

Street warden at bottom of Stephenson Place, December 2016

Street warden at bottom of Stephenson Place, December 2016. The CAF trams used on Midland Metro are fitted with various types of glazing made in France, Spain, and the Czech Republic

In the view of the Beleben blog, there are questions to be asked about the crashworthiness of the vehicles used on Tramlink, and other GB systems.

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Written by beleben

December 7, 2016 at 1:07 pm

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  1. My immediate reference point here was the fatal crash of the Aberdeen sleeper at Morpeth in 1969, which triggered the fitting of permanent AWS magnets at 500 PSR sites where the speed limit was significantly lower than the ruling line speed. With a quixotic irony the signalling configuration and other factors at Morpeth meant that although a key location for the AWS on the PSR it could not be fitted and in 1984 the Up sleeper derailed at the same location, demolishing a bungalow in the process.

    Significantly the 1989 report, whilst noting the the driver had failed to realise where his train was, and running through the 40mph restriction at the 80mph line speed, the locomotive (Class 55) stayed on the rails, and calculations indicated that the train would have stayed on the rails at a speed of up to 97mph – typically most trains will stay on the rails going round a curve at twice the posted speed and a bit more but passenger comfort is, putting it mildly, somewhat compromised.

    What happened is often referred to as the swiss cheese slices effect, where a stack of causal factors all fall into place.

    Whilst posted as a 17 chain curve, there was one short section where the threepenny bit factor reduced the effective radius to 15.5 chains.

    Then there was a slightly higher presence of small voids in the ballast allowing the track slightly greater movement under load

    The leading carriage was a BG van with a substantial part of its load, newspapers, which were able to move through the centrifugal forces induced by taking the curve at excessive speed.

    This curve is like most changes of direction or gradient on railway track, set out with transition radii on approach and exit in the horizontal plane and a similar transition in the track cant or superelevation of the outer rail to reduce rate of change and effects of lateral forces on the train and track. Tram track, especially where it is embedded in the street, is often not afforded the luxury of the same precision of adjustment for cant and transition curves in the horizontal, and given the severity of some gradient changes, the vertical planes. The time taken to get that track right at the corner of Stephenson Street and Corporation Street crucially highlights this issue, and delivers a long term maintenance burden.

    Any weakening in the security of the embedded rails can deliver wear problems, and movement especially of the outer rail, which may even rotate (outwards) in the vertical plane, away from the vertical setting used for most grooved rail installation. Plain track – for most trams has rails inclined inwards at 1 in 40, but for rail vehicles this generally increases to 1 in 20, as the wheel profile of rail vehicles makes greater use of conicity rather than flange contact to steer the wheels around curves, that said the extensive use of former rail lines for Croydon and Manchester especially, sees that standard varied. I’d commend the research paper from the Rail Technology Unit at Manchester Metropolitan University – “Determination of Tramway Wheel and Rail Profiles to Minimise Derailment” for a greater insight.

    We now know that an earlier overspeed incident at the same location was processed, initially by the Police, but did not go through the same process as a rail overspeed event, and now also hear of a Manchester tram driver sacked for speeding – but without the learning points (eg measures to prevent the driver being able to go too fast, or remind them of a speed limit more effectively) which would be delivered by an RAIB review.

    The Manchester incident also occurred on the former railway formation, with track which reports suggest is still maintained to a standard capable of taking a heavy rail train, and from the pictures at a speed well above the posted limit for the trams. that lower speed in this place is more likely to be set by the proceed on sight operation of the trams, and the very worrying views you get from the rear of a stopped tram when the following tram comes around the corner, and relying solely on the driver (?) stops less than 20 metres from the back of your tram. Given the reports and experiences of tram drivers not responding to speed limits and other ‘vigilance’ issues this is surely a crash waiting to happen, especially if the driver fails to stop at the entry to a single track 2-way section.

    DH

    December 9, 2016 at 11:33 am


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