  Reinforcement Learning (RL) has made promising progress in planning and
decision-making for Autonomous Vehicles (AVs) in simple driving scenarios.
However, existing RL algorithms for AVs fail to learn critical driving skills
in complex urban scenarios. First, urban driving scenarios require AVs to
handle multiple driving tasks of which conventional RL algorithms are
incapable. Second, the presence of other vehicles in urban scenarios results in
a dynamically changing environment, which challenges RL algorithms to plan the
action and trajectory of the AV. In this work, we propose an action and
trajectory planner using Hierarchical Reinforcement Learning (atHRL) method,
which models the agent behavior in a hierarchical model by using the perception
of the lidar and birdeye view. The proposed atHRL method learns to make
decisions about the agent's future trajectory and computes target waypoints
under continuous settings based on a hierarchical DDPG algorithm. The waypoints
planned by the atHRL model are then sent to a low-level controller to generate
the steering and throttle commands required for the vehicle maneuver. We
empirically verify the efficacy of atHRL through extensive experiments in
complex urban driving scenarios that compose multiple tasks with the presence
of other vehicles in the CARLA simulator. The experimental results suggest a
significant performance improvement compared to the state-of-the-art RL
methods.
