The Dichotomous Coverage Model: When Formal Networks and Informal Paratransit Collide in a Megacity

Across Global South megacities, bus reforms seek to transform informal paratransit into formal networks. However, even successful formal services on major corridors coexist with thriving informal sectors in unreached spaces. This paper introduces the Dichotomous Coverage Model to explain this phenomenon, drawing on Metropolitan Lagos, where a century of reform has produced a bifurcated mobility landscape. Integrating spatial interaction theory, institutional analysis, and empirical evidence from the Lagos Bus Reform Initiative, including a commuter survey (n=1,023) and operational data from 120 formal routes, the model argues that formal networks and informal paratransit occupy distinct niches: spatial legibility versus operational penetration; scheduled reliability versus spontaneous responsiveness; infrastructural formality versus institutional embeddedness; network hierarchy versus capillary reach. Illustrative evidence from fourteen global cities suggests recurring spatial typologies of formal-informal coexistence. The paper concludes that the complete formalisation may be unattainable; sustainable mobility requires strategic integration that leverages the complementary strengths of both systems.