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PPM, the Public Performance Measure, is the percentage of trains that arrive 'on time' at their destination, regardless of who has impacted on the train service. Rather than simply focussing on trains arriving exactly on-time ('Right Time'), a reasonable tolerance is built in to the calculation.

  • For long-distance services, 'on time' describes trains up to 10 minutes late
  • For shorter distance services, 'on time' describes trains up to 5 minutes late

The PPM figures on the Open Data feed differs slightly from the official PPM figures issued by Network Rail:

  • The RTPPM data calculates PPM on the basis on trains arriving at their destination between 0200 and 0159 the next day.
    • If a train starts its journey before midnight and finishes after 0200, it will not be counted in the day's figures.
    • If a train starts after midnight and finishes after 2am, it will be counted
    • If a train starts its journey before midnight but doesn't arrive at its destination until after 0159, it will not be counted
  • All VSTP schedules are counted, i.e. trains that are planned or altered on the day they are due to run are included in the RTPPM figures, but would normally be excluded from the official PPM report
  • Where a train has been cancelled prior to the day it runs, the RTPPM system will process that cancellation. If the train then actually runs, it will not be counted for PPM purposes, as the system would have already processed the planned cancellation and will treat the actual train as a duplicate
  • Non-applicable trains are included in the RTPPM calculations, but not in the official PPM figures
  • The system does not record 'fail to stop' events, diversions from the planned route or trains starting away from the planned origin. It does, however, count short terminations
  • The system rounds down all percentage values to the nearest whole number, so 92.7% will be displayed as 92%
  • The system cannot detect missed stops, which the official system picks up as a PPM failure through manual edits
  • For First Capital Connect services, RTPPM only registers a PPM success or failure at the service's destination. This differs from the official system, which registers the services twice - once at Blackfriars (northbound) or Farringdon (southbound), and once at its destination

'CaSL' refers to Cancellations and Significant Lateness. The figure is made up by adding together the number of cancelled trains and the number of trains more than 29 minutes late. The percentage is derived from taking the total number of CaSL'd trains diving by the total number of trains due to run up until that point.