The interaction between soil and pile is an important factor in the performance assessment of roadside piled-barrier systems under vehicle collision. Previous studies have primarily focused on the structural aspects of the system in numerical simulations of full-scale crash tests, failing to consider the effect of soil nonlinear behaviour on roadside barrier crashworthiness. In this study, we first evaluate commonly used soil constitutive models in LS-DYNA for full-scale crash simulations. The primary goal is to assess the suitability of these models for simulating piled barriers under impact, highlighting the limitations. In the second part of the paper, we propose a new soil constitutive model developed based on the Mohr–Coulomb and FHWA constitutive models. This model can effectively represent critical soil features, including strain softening and strain rate effects, essential for more accurate soil-pile simulation under impact. The proposed soil constitutive model is validated through a series of triaxial test results in element scale and will be further developed to be used in boundary-value simulations.