  High-quality traffic flow generation is the core module in building
simulators for autonomous driving. However, the majority of available
simulators are incapable of replicating traffic patterns that accurately
reflect the various features of real-world data while also simulating
human-like reactive responses to the tested autopilot driving strategies.
Taking one step forward to addressing such a problem, we propose Realistic
Interactive TrAffic flow (RITA) as an integrated component of existing driving
simulators to provide high-quality traffic flow for the evaluation and
optimization of the tested driving strategies. RITA is developed with
consideration of three key features, i.e., fidelity, diversity, and
controllability, and consists of two core modules called RITABackend and
RITAKit. RITABackend is built to support vehicle-wise control and provide
traffic generation models from real-world datasets, while RITAKit is developed
with easy-to-use interfaces for controllable traffic generation via
RITABackend. We demonstrate RITA's capacity to create diversified and
high-fidelity traffic simulations in several highly interactive highway
scenarios. The experimental findings demonstrate that our produced RITA traffic
flows exhibit all three key features, hence enhancing the completeness of
driving strategy evaluation. Moreover, we showcase the possibility for further
improvement of baseline strategies through online fine-tuning with RITA traffic
flows.
