Transitioning towards less car-reliant low-carbon mobility systems is not easy. Scholars indicate the transition will involve dramatic social, cultural and technical rearrangements. Where does this leave the profession of transport planning? Practitioners really only have two viable alternatives: constructing more road space for more modes or allocating existing space for specific mode priority and/or to reduce travel. Whereas the former is informed by a predict-and-provide ideology and now largely discredited by scholars, the later continues to evolve and be refined and provides the backdrop for this presentation. Drawing from sociology of scientific knowledge (SSK), the presentation discusses professional decision-making processes, practices and knowledge employed to allocate road space. A case study of transport planning in Melbourne, Australia is used to develop an argument for why examining the practice of transport planning still matters. The presentation begins by summarising how SSK helps reconcile conflicting interpretations of transport planning practice held within different scholarly bodies of knowledge. Examples of practice are then used to demonstrate how developing professional processes, practices and knowledge is informed and enacted through practitioners actively engaging, and/or reacting to and against, technology and infrastructure.