  Deep reinforcement learning (DRL) has shown remarkable success in complex
autonomous driving scenarios. However, DRL models inevitably bring high memory
consumption and computation, which hinders their wide deployment in
resource-limited autonomous driving devices. Structured Pruning has been
recognized as a useful method to compress and accelerate DRL models, but it is
still challenging to estimate the contribution of a parameter (i.e., neuron) to
DRL models. In this paper, we introduce a novel dynamic structured pruning
approach that gradually removes a DRL model's unimportant neurons during the
training stage. Our method consists of two steps, i.e. training DRL models with
a group sparse regularizer and removing unimportant neurons with a dynamic
pruning threshold. To efficiently train the DRL model with a small number of
important neurons, we employ a neuron-importance group sparse regularizer. In
contrast to conventional regularizers, this regularizer imposes a penalty on
redundant groups of neurons that do not significantly influence the output of
the DRL model. Furthermore, we design a novel structured pruning strategy to
dynamically determine the pruning threshold and gradually remove unimportant
neurons with a binary mask. Therefore, our method can remove not only redundant
groups of neurons of the DRL model but also achieve high and robust
performance. Experimental results show that the proposed method is competitive
with existing DRL pruning methods on discrete control environments (i.e.,
CartPole-v1 and LunarLander-v2) and MuJoCo continuous environments (i.e.,
Hopper-v3 and Walker2D-v3). Specifically, our method effectively compresses
$93\%$ neurons and $96\%$ weights of the DRL model in four challenging DRL
environments with slight accuracy degradation.
