C120 steel sections are the most widely used post shapes in European guardrail designs. The design length of these posts is determined based on guardrail containment level and engineering judgment. The soil properties where these posts are embedded are usually not considered in design. It is a well-known fact that the crash test performance of soil embedded posts depends mostly on post-soil interaction and post embedment depth (PED). In this study, a series of field impact tests were performed on soil embedded C120 posts to determine optimum PED for three different soil conditions. Seven different PED varied from 650 to 900mm was used for each soil type. Based on these findings a full-scale crash test is performed on a guardrail to verify optimum PED for hard soil conditions. With the use of optimum length guardrail posts considerable amount of installation time, labor and material savings are expected.