For over 50 years, studies of soil-pipe interaction have provided methods to predict vertical deflection of buried flexible pipes. Several of these methods are widely used in standards. However, these methods do not account for many of the recognized parameters that affect buried pipe behavior. Based on recent research findings, empirically-based modifications are introduced to the original Spangler approach to obtain a new calculation method for estimating vertical flexible pipe deflection. Development, applications and limitations of this method are presented. Comparison studies of the new method and that presented in ANSI/AWWA C950-88 "AWWA Standard for Fiberglass Pressure Pipe" (which is based on the modified Iowa formula) versus actual field measurement data are included. These studies present correlation of predicted versus measured values as well as similarities and differences between the methods.