Modeling and investigating the properties of fundamental diagrams (FDs) in mixed traffic, which encompasses heterogeneous with non-lane-based flow, has been one of the emerging research areas in the past few years. The main challenges in modeling are: estimating accurate steady-state (ss) points based on empirical observations and properly representing FDs in mixed traffic conditions. The first part of this work uses the traditional discretization approach and the optimal time–space window to apply Edie’s generalized definitions to estimate the traffic flow variables and the steady states. The second part of the work involves a trajectory shear mapping method to estimate less-scattered FDs. Finally, the shape of the FDs are determined, and their properties are studied by developing area occupancy-based (ao) normalized flow and speed models. Empirical observations from multiple locations show that the power-law relationships seem to be the best fit based on the ao-based representation of the fundamental parameter that indicates the possibility of universality in the FDs from the mixed traffic conditions. •Shear transformation of trajectories reduces scatter in fundamental diagrams.•Providing insights into Manna universality class behavior of mixed traffic.•Confirmation of location invariant power-law relationships.•Algorithm with optimal time-space steps simplifies steadystate point identification.