The Oregon Department of Transportation (ODOT) and its partner agencies chose RSG to develop a state-of-the-art standardized population synthesis program. This new tool, called PopulationSim, replaced multiple population synthesis tools being used throughout the state for urban, statewide, and strategic modeling. Unlike other population synthesis programs, PopulationSim handles multiple geographies and avoids algorithmic errors. In population synthesis tools, sequential zone processing can result in some zones being allocated most of the error between controlled and realized totals, but PopulationSim uses a simultaneous list balancer and integerizer to eliminate error. PopulationSim also includes comprehensive tracing of all calculations and a small geographies mode where a population is generated for a handful of model zones (e.g., traffic impact studies) to improve user experience.
Unlike many population synthesizers in use, we developed PopulationSim using software engineering best practices. The system is under continuous integration, which means the software and documentation are automatically built and tested so revisions to the platform cannot be accepted until verified; this lessens the likelihood of bugs being introduced. ODOT and others have since used the tool to generate synthetic populations in their regions as inputs to travel demand models. PopulationSim is an open platform for population synthesis and is implemented in the Python-based ActivitySim modeling framework. The software is expected to support the ActivitySim project.