In no field of planning is there more reliance on technical-rational decision-making processes than transportation planning. In Australian cities transport planners still heavily rely upon complex, quantitative transport models, especially the four-step model (FSM) and its variants, used at the regional, metropolitan and corridor levels of analysis. While it is beyond the scope of this paper to provide a detailed critique of each stage of the FSM, there are numerous problems with its use that need to be addressed. This paper examines the empirical shortfalls of the technical-rational process, highlighting the reliance on a select few experts, limited public participation in modelling processes, and decision-makers who have little understanding of the methodological limitations inherent in transport modelling advice. Model deficiencies do not allow for, and may actually impede consideration of many of the most important emerging issues within cities, including road pricing, climate change and oil vulnerability, as well as long-held concerns such as land use changes, induced travel, the environment and sustainability. This paper identifies numerous inter-related concerns about the broader policy and political dimensions of technical-rational decision-making in the transport sector, and recognises the main tools used in technical assessments.