SAMPLE SIZE DETERMINATION FOR TRAVEL TIME AND DELAY STUDIES

Abstract

Based on the central-limit theorem, sample means of travel times are assumed to have a normal distribution, regardless of the actual distribution of the population of travel times along a study route. Using this assumption, the techniques of statistical quality control are applied to provide a procedure for sample size determination. This procedure is applicable for both the license-plate and the test car techniques; it is also used for estimation of sample sizes for travel time and delay studies that involve either general travel conditions for all vehicles along a study route, or for only public transportation vehicles on scheduled routes.