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    • djf01 posted
    Posted in Sydney Suburban » NSW Future Rail Plan - NWRL/Metro/Harbour Crossing

    Ah, minimum separation rather than stopping time (the phrase you used before), that makes more sense. Twice the minimum stopping time is what I would have guessed as the minimum safe separation. Good to know.

    ...

    The part you said before that I really found strange was that such densities would require top speeds of under 40km/h to comply with Australian standards. Your clarifications don't really seem to support that, unless that was stated assuming that drivers and block signalling were involved.

    darkmage35


    You're right, I think I stuffed up and transposed stopping distance/time and minimum separation in my head before posting that comment about 40kph.

    BTW, with 3 phase block signalling (we actually have 5 phase on CityRail) the absolute minimum achievable separation is effectively 4 stopping lengths.  That's because the trailing train "has" (AFAIK there are no hard an fast quantitative rules on this yet) to decelerate prior to passing a signal at caution (this adds 1), and even 3 stopping lengths is only right when the trains are optimally positioned relative to the blocks.  The separation will vary between being 100% optimal for block placement, and 100% non-optimal regarding block placement, which means you need to add and extra block, effectively another stopping distance.

    The other thing you need to consider is these stopping distances need to be calculated based on the fleet's worst performing vehicles in the worst (reasonably) possible conditions ie, wet/lubricated braking surfaces, fully loaded vehicles at the wrong end of their maintenance cycle.

    Edit history

    Edited 12 Dec 2013 01:40, 8 years ago, edited by djf01

    Ah, minimum separation rather than stopping time (the phrase you used before), that makes more sense. Twice the minimum stopping time is what I would have guessed as the minimum safe separation. Good to know.

    ...

    The part you said before that I really found strange was that such densities would require top speeds of under 40km/h to comply with Australian standards. Your clarifications don't really seem to support that, unless that was stated assuming that drivers and block signalling were involved.

    darkmage35


    You're right, I think I stuffed up and transposed stopping distance/time and minimum separation in my head before posting that comment about 40kph.

    BTW, with 3 phase block signalling (we actually have 5 phase on CityRail) the absolute minimum achievable separation is effectively 4 stopping lengths.  That's because the trailing train "has" (AFAIK there are no hard an fast quantitative rules on this yet) to decelerate prior to passing a signal at caution (this adds 1), and even 3 stopping lengths is only right when the trains are optimally positioned relative to the blocks.  The separation will vary between being 100% optimal for block placement, and 100% non-optimal regarding block placement, which means you need to add and extra block, effectively another stopping distance.

    The other thing you need to consider is these stopping distances need to be calculated based on the fleet's worst performing vehicles in the worst (reasonably) possible conditions ie, wet/lubricated braking surfaces, fully loaded vehicles at the end of their maintenance cycle.