The management of national road bridge inventories in developing regions is constrained by fragmented data systems, limited monitoring capacity, and the absence of integrated decision-support frameworks capable of translating condition data into prioritised maintenance programmes. This paper presents the design, formalisation, and validation of an integrated Building Information Modelling–Geographic Information Systems (BIM-GIS) framework for the lifecycle asset management of national road bridge inventories, with particular application to the South Sudan national road network and the broader East African Community (EAC) infrastructure corridor. The framework establishes a bidirectional data exchange architecture between IFC-compliant BIM models and georeferenced GIS databases, enabling simultaneous geometric, structural, and spatial analysis of bridge assets within a unified platform. A formal data schema is developed that maps structural element attributes — including material properties, condition ratings, inspection histories, and maintenance records — to geospatial objects with full topological relationships to the road network. Mathematical formulations for condition index computation, deterioration prediction using Markov chain transition matrices, and maintenance prioritisation using multi-criteria decision analysis (MCDA) are derived and implemented within the framework. Spatial query performance benchmarks demonstrate that the BIM-GIS integrated system achieves a 62% reduction in query response time for asset inventories exceeding 10,000 bridge records compared to non-indexed GIS systems. Lifecycle cost analysis shows a net present value saving of approximately USD 2.4 million per 100 km of national highway over a 50-year analysis horizon when the BIM-GIS opti