Evaluating reinforcement learning state representations for adaptive traffic signal control

Reinforcement learning has shown potential for developing effective adaptive traffic signal controllers to reduce traffic congestion and improve mobility. Despite many successful research studies, few of these ideas have been implemented in practice. There remains uncertainty about what the requirements are in terms of data and sensors to actualize reinforcement learning traffic signal control. We seek to understand the data requirements and the performance differences in different state representations for reinforcement learning traffic signal control. We model three state representations, from low to high-resolution, and compare their performance using the asynchronous advantage actor-critic algorithm with neural network function approximation in simulation. Results show that low-resolution state representations (e.g., occupancy and average speed) perform almost identically to high-resolution state representations (e.g., individual vehicle position and speed). These results indicate implementing reinforcement learning traffic signal controllers may be possible with conventional sensors, such as loop detectors, and do not require sophisticated sensors, such as cameras or radar.