This paper details the development process and model architecture used in the University of Washington's EcoCAR 2 hybrid supervisory controller. The EcoCAR 2 project challenges 15 universities across North America to create a hybrid vehicle that most effectively minimizes emissions and fuel consumption while still maintaining consumer acceptability.The supervisory controller for the University of Washington was designed to distribute torque to the various electric and combustion drive systems on a parallel though the road plug-in hybrid electric vehicle using Simulink and Stateflow. The graphical interface of Simulink offers some distinct advantages over text-based programming languages. However, there are also significant challenges posed by the software, particularly when several controls engineers are working in parallel on a large model with some type of version control.In order to address some of these challenges, it is necessary to structure the model so that different areas of the program are properly partitioned to avoid instances of conflicting changes from different developers. By effectively partitioning the hybrid supervisory controller, it becomes much easier to implement the use of linked Simulink library blocks in the model. A variety of libraries can be created to monitor different systems of components.The supervisor model structure outlined in this paper uses these concepts to effectively allow for parallel code development. This structure is examined in detail to serve as an example for laying out out a Simulink and Stateflow model with highly partitioned subsystems.