Linear infrastructure projects pose unique geotechnical challenges as the long narrow corridor often traverses a wide range of topography, geological settings and natural landforms. The early development of engineering geological models (EGMs) can provide invaluable input into a project from pre-tender site investigation through to construction. The early development of a conceptual EGM can inform the site investigation locations, techniques and tools utilized to gather data. Continually updating the EGM throughout the site investigation phase ensures that critical information is gathered where needed to inform the geological, geotechnical and analytical models used throughout the design phase. Confirmation of the EGM during construction allows assumptions made during design to be validated and provides opportunities to re-evaluate the design, if required. The process used to develop the EGM must consider the model’s uses at various stages of the project. The basis of the project geological units and their associated characteristics varies significantly depending on the project type, location, design and analytical requirements. This paper explores an approach to rationally defining the EGM framework for linear infrastructure, including geological and geotechnical unit characterization and definition to assess the range of information required for each design and assessment process required. Unit characterization must consider the range of measurable properties that will affect and are relevant to the specific design outcomes. This context-specific approach ensures that the data collected, categorized and modelled is appropriate and useful throughout the project’s life. Examples of the use of the approach on linear infrastructure projects are provided.