Customized Sampling Plans: A Guide to Alternative Sampling Techniques for National Transit Database (NTD) Reporting

For estimating the system total unlinked passenger trips and passenger miles of a fixed-route bus system for the National Transit Database (NTD), the FTA approved sampling plans may either over-sample or do not yield FTA's required confidence and precision levels for the specific conditions of a transit agency.This guide helps transit agencies avoid these problems by developing their own sampling plans for fixed-route bus services.Detailed steps are provided to calculate the statistical variation in passenger miles and unlinked passenger trips and the correlation between them.The sampling plans that transit agencies develop using this guide maintain the main features of the original FTA plans.More important, transit agencies can easily use this guide to develop their own sampling plans in an Excel environment using three existing pieces of information: an NTD sample that they have collected with their current FTA approved sampling plan, their annual days of service, and daily total number of oneway bus trips.This guide complements FTA Circular C2710.1A in that transit agencies first select one of their own sampling plans that best meets their staffing needs, and then follow the procedures in the Circular on sampling and collecting field data.17.