The article examines the determinants of pickup and delivery stop time in the U.S. The analysis of the causal factors of pickup and delivery stop time have depended on either a limited number of observations of a single carrier or on the data gathered by the Interstate Commerce Commission as part of its periodic regional cost studies. In this study, the participating carriers were 29 volunteers of various sizes and regional locations, which collectively cover the 48 states. The purpose of the classification item number was to obtain an index of density. The analysis used herein was multiple regression analysis. This method, when suitably employed, permits the simultaneous analysis of several explanatory variables, avoids arbitrary allocations, and produces a measurement of statistical reliability. The conclusions are, the constant stop time per shipment represents a sizeable proportion of total stop time for shipments of average or smaller size, weight is the most significant factor determining the variable portion of stop time and the number of pieces and density are also significant determinants of stop time, and their inclusion in the allocation formulas may be warranted.