In order to assess pressure distributions within the track and support structure, earth pressure cells have been installed in selected hot mix asphalt (HMA) trackbeds on a CSX Transportation heavy tonnage revenue freight line and at the TTCI heavy tonnage test track in Pueblo. The measured values of pressure distribution within each layer were used to establish a pressure index. This pressure index is the ratio of pressure at the interface of a layer, to the predicted bearing capacity of the layer. A pressure index value of one implies failure of the layer. The pressure index and other measures of structural performance such as track modulus and subgrade stiffness were assessed. From these assessments, relationships were established whereby the pressure distribution and deflection characteristics of the trackbed were quantified in terms of material type and layer thickness. Thus, allowing for a rational performance assessment of the overall trackbed system.