Leaves On The Line Caused The Salisbury Crash

Discussion in 'Off Topic' started by Daytona, Feb 21, 2022.

  1. Daytona

    Daytona Active Member

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    Basingstoke train skidded, for ~1 mile, SPADed and hit a Portsmouth train at a junction. It's speed only reduced by ~30mph from 86mph

    21 "around 1,600 metres after passing signal SY29R and with the train travelling at 86 mph (138 km/h) on level track, the driver made a step 2 brake application. This was in accordance with his usual practice and was done with the intention of being able to stop the train at signal SY31, which was at this point around 1,500 metres away. Although the train’s speed began to reduce, analysis of OTDR data shows that its wheels began to slide almost immediately after this brake application was made. The driver made a full-service brake application five seconds later and moved the brake controller to the emergency brake position after a further six seconds. The train’s wheel slip/slide prevention (WSP) system was active throughout this braking, but the train’s speed reduced only slowly"

    24 "At the point where the two trains collided, train 1L53 was travelling at between about 52 and 56 mph (84 and 90 km/h)."

    14 "Before reaching signal SY31, trains approaching the junction on the down main line pass signal SY29R and signal SY29, which are respectively 3,314 metres and 978 metres from the point of collision."

    35 "evidence of railhead contamination at twelve sample locations from 80 miles 32 chains to immediately before the point of collision at 82 miles 36 chains, a length of two miles (3.2 km)."

    36 "This deposit consisted of leaf material which had been crushed under the wheels of passing trains and which is often associated with low adhesion conditions"

    36 "Wet values of the coefficient of friction measured as part of the post-accident survey were found to be between 0.2 and 0.02, suggesting that there was low friction between the wheels and the railhead. The average rate of deceleration of train 1L53 suggests adhesion levels closer to the 0.02 value"

    43 "there would have been an interval of 36 hours between the RHTT [Rail Head Treatment Train] runs over the weekend"

    https://assets.publishing.service.g...IR012022_220221_Salisbury_Tunnel_Junction.pdf
     
    Last edited: Feb 21, 2022
  2. Daytona

    Daytona Active Member

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    So I guess it would have required closer to 3 miles to stop from 86mph, starting a mile before the double yellow...

    The max speed for the conditions would look to be significantly below the 95mph line speed. Closer to 60mph plus whatever safety margin they use. And that's with a driver braking from the double yellow.

    So the track looks unserviceable for the schedule.

    Just wondering if the latest trains can feed back track conditions in real time ? ETCS ?
     
    Last edited: Feb 21, 2022
  3. FD1003

    FD1003 Well-Known Member

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    I don't think so, as far as I know these systems only have as input the train data (so I would imagine some performance data from the manufacturer + train specific data entered by the driver before departure - like train weight, lenght, etc...). Using this data the system extrapolates the braking curve that will be enforced, which is closer to a normal brake application rather than an emergency brake one, so in case the emergency brakes are activated there is still the necessary buffer caused by lower adhesion conditions such as snow. But this was far from normal.

    As an example, for british trains ETCS could enforce a braking curve applicable to a step 2 braking application, so if you were to overspeed and the emergency brakes were activated, the train would end up stopping faster than the calculated curve.
     
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  4. KiwiLE

    KiwiLE Well-Known Member

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    ETCS is after my UK time, but as a trainee driver, we were always aware of leaf fall, and the obvious potential for missed station stops. Oxenholme was always interesting in autumn, and I had to set back to the platform on 2 occasions, as I was under 1/4 mile past.
    Freight was no different. I remember doing 75mph in a 92 and a long intermodal train, getting 2 yellows near Lancaster, putting the train brakes on and the speedo went to 0 immediately, plus the whole train sliding on grease.

    There is a fine transition period between having no problem at all, and "slippy season" hitting. The finding out bit isn't nice.
     
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