  We present a multi-agent Deep Reinforcement Learning (DRL) framework for
managing large transportation infrastructure systems over their life-cycle.
Life-cycle management of such engineering systems is a computationally
intensive task, requiring appropriate sequential inspection and maintenance
decisions able to reduce long-term risks and costs, while dealing with
different uncertainties and constraints that lie in high-dimensional spaces. To
date, static age- or condition-based maintenance methods and risk-based or
periodic inspection plans have mostly addressed this class of optimization
problems. However, optimality, scalability, and uncertainty limitations are
often manifested under such approaches. The optimization problem in this work
is cast in the framework of constrained Partially Observable Markov Decision
Processes (POMDPs), which provides a comprehensive mathematical basis for
stochastic sequential decision settings with observation uncertainties, risk
considerations, and limited resources. To address significantly large state and
action spaces, a Deep Decentralized Multi-agent Actor-Critic (DDMAC) DRL method
with Centralized Training and Decentralized Execution (CTDE), termed as
DDMAC-CTDE is developed. The performance strengths of the DDMAC-CTDE method are
demonstrated in a generally representative and realistic example application of
an existing transportation network in Virginia, USA. The network includes
several bridge and pavement components with nonstationary degradation,
agency-imposed constraints, and traffic delay and risk considerations. Compared
to traditional management policies for transportation networks, the proposed
DDMAC-CTDE method vastly outperforms its counterparts. Overall, the proposed
algorithmic framework provides near optimal solutions for transportation
infrastructure management under real-world constraints and complexities.
