Poisson’s ratio is an important material property needed for mechanistic-empirical base-reinforced pavement design procedures. However, earlier work has shown that determining Poisson’s ratio by measuring lateral strain in an in-air tension test led to misleading values that were not representative of those pertinent to design applications. Since Poisson’s ratio describes the effect of increased geosynthetic tensile stiffness when load is applied simultaneously in both material directions, it makes sense to devise a test where load is applied in this manner and Poisson’s ratio is determined from the test results. Such a test is a biaxial tension test where a sample is cut in the form of a cross and load is applied in both material directions. Only a few biaxial testing devices currently exist. One of these devices was developed in the United Kingdom. Data from this device was examined by members of this project team and used to calculate Poisson’s ratio. This method showed good promise for providing this important material property, however a standardized test protocol for determining Poisson’s has not been established. Test specifications such as sample size, configuration, loading type, and loading rate still need to be defined for a standardized test so that this material property can be used for geosynthetic reinforced pavement design.