Pan-regionalism has always been an attractive co-operation strategy among neighbouring national realities, promising more stable economic development and more constructive social relations. Regionalisation efforts are arguably the preferred diplomatic strategy of the 21st century, and outstanding models are being implemented all over the world. Asia as a whole has almost been saturated by co-operation agreements, although amongst all of them, the picture that has in recent decades been delineating around Southeast Asia deserves particular attention. Efforts towards the harmonisation of intra-regional flows have begun to bear fruit, and people (thus goods and information) have started to move more freely across the sub-region’s internal frontiers. This research project looks at how ‘sub-regionalism’ in mainland Southeast Asia is given different interpretations depending on what is at stake and who is involved. In particular, a comparative analysis of three of the many layers of influence is taken into account, at international, regional, and ground level. Each of those layers has to be understood through the perspective of the people who pull its strings, as people’s perceptions are far more powerful and have a far more decisive impact on interdependence than policies do. Recent responses to the planning and management of intra-regional arteries throughout the sub-region (the so-called socio-economic corridors) will be taken as a case study that will help us gauge the attitudes of Development Agencies (international level), Southeast Asian governments (regional level), and local people (ground level) towards differing senses of commonality regarding one of the region’s most important as controversial assets: mobility.