Shortcomings were identified in historic dynamic guardrail post testing methods that could overestimate the strength of guardrail posts by a factor of two. This inaccuracy resulted from the influence of inertia that was not previously accounted for during dynamic component testing. The effects of inertia were verified and quantified with several analysis methods including nonlinear finite element analysis, which was used to develop a computer simulation of the dynamic tests. Several alternative testing procedures that could significantly reduce the effects of inertia were identified and investigated. One of these testing alternatives-use of a crushable impact head-was shown with computer simulation to reduce the effects of inertia and maintain the benefits of strain rate effects. The use of such an impact head is recommended for all future dynamic post strength testing. The results of the study imply that changes should be made not only in the standard design procedures used for guardrail and other vehicular barriers, which are clearly influenced by inertial effects, but in all designs that are based on dynamic strength testing. Dynamic testing is very common in the field of transportation engineering and care should be taken to ensure that inertial effects are considered when performing such tests.