Macroscopic fundamental diagrams (MFDs) describe the relationship between aggregated flow and density in urban road networks. First observed empirically in 2008, MFDs are now widely studied in the traffic engineering literature as a possible means for implementing perimeter control of key regions in an urban network (e.g. Melbourne's CBD). The fundamental statistical methodology addressing how to obtain well-defined MFDs from data remains largely unexplored however. This project seeks to address this theoretical gap, with the ultimate goal of controlling road networks in a reliable and robust way, and thereby reducing congestion.