DETERMINATION OF SAMPLE SIZES FOR TRAVEL TIME STUDIES

Abstract

Existing procedures to estimate minimum sample sizes for travel time studies are examined, and new tables are provided for estimating sample sizes based upon a larger selection of confidence intervals. Two types of formulations are commonly used for estimating minimum sample sizes: (1) based on sample ranges; and (2) based on sample standard deviations. A hybrid formulation is proposed that produces a minimum sample size closest to those produced with the standard deviation formulation, but that takes into account average sample range, which is more easily understood and calculated by field personnel.