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Using Archived AVL-APC Data to Improve Transit Performance and Management (2006) / Chapter Skim
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9.2 Accuracy and Sample Size Needed for Passenger-Miles
Pages 63-65

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From page 63...
... A reasonable target precision to ensure that the route is neither overcrowded nor overserved is 5% or 6%, effectively limiting permissible load bias on crowded segments to about 5%. Sample size needed to achieve this target precision depends on the bias and cv of load estimates.
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From page 64...
... The weekday sample size requirement is where N2 equals the number of weekday timetable trips and rse is the permitted relative standard error from Table 11. For bias up to 8% and for all but the smallest transit systems, the N2 term will control; that is, it is sufficient to simply observe every timetable trip once.
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From page 65...
... This approach assumes that instrumented buses, for reasons beyond NTD passenger-miles estimation, are being circulated in a manner that covers the entire schedule regularly. Intentional sampling methods with limited sample sizes are clearly inferior, unless data processing procedures are still so undeveloped that each trip's data must be manually checked.
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Key Terms

  • relative standard
  • timetable trip
  • timetable trips
  • weekday timetable
  • effective penetration

  • permitted relative
  • fleet penetration
  • penetration rate
  • required versus
  • target precision

  • peak load
  • load estimates
  • adequate sample
  • data recovery
  • standard normal

  • selected values
  • recovery rate
  • route average
  • coverage rate
  • transit agency

  • labor intensive
  • involve unintentional
  • alternative sampling
  • error falls
  • careful rotation

  • term approaches
  • collection design
  • counts themselves
  • apcs collect
  • timetable size


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