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One Step is Enough: Multi-Agent Reinforcement Learning Based on One-Step Policy Optimization for Order Dispatch on Ride-Sharing Platforms
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Proposes ST-GRPO and OSPO, critic-free multi-agent policy optimization for AV order dispatch that replaces value baselines with fleet-average rewards (ST-GRPO) or one-step group-normalized rewards (OSPO), using MLP policies on Manhattan and Queens ride-hailing data.
Problem
Order dispatch for ride-sharing fleets of autonomous vehicles requires MARL, but value-function (Q/V) estimation in large, highly stochastic urban environments is biased and unstable, hurting training efficiency and policy quality.
Approach
Exploit fleet homogeneity and short-memory mixing to show agent value functions share a common time-varying baseline, so advantages can be computed from the fleet-average reward-to-go (ST-GRPO) or, under bounded-value and mixing conditions, from immediate group-normalized rewards alone (OSPO), removing the critic entirely.
Key results
- On Manhattan, OSPO achieves the best reward (11.00 ± 2.63 ×10^3), service rate 1.00, and pickup time 6.71 min versus 8.67 for DeepPool and 8.10 for Hoppe et al.
- ST-GRPO achieves pickup time 7.33 and service rate 1.00 on Manhattan with a 20K-parameter MLP and 5.17 GB GPU occupation.
- On Queens, OSPO reports reward 5521.74 and service rate 0.67 versus 0.66 for BMG-Q, with pickup time 11.88 versus 12.30 for DeepPool.
Surprising findings
- OSPO, which uses only immediate group-normalized rewards with no long-horizon bootstrapping, outperforms ST-GRPO that uses fleet-averaged reward-to-go.
- MAPPO failed to converge due to the curse of dimensionality in its centralized critic, and only IPPO was competitive among the policy-gradient baselines.
Limitations
- Theoretical guarantees rely on assumptions (homogeneity, uniform beta-mixing, bounded V-values) that may not hold during training exploration; the authors add a heuristic regularization term to address this.
- Evaluation limited to two NYC datasets with a 30-minute episode horizon; results on Queens show ST-GRPO and OSPO gains are small in service rate.
- Reported differences are small in several metrics (e.g., service rate 0.64 vs 0.67 on Queens) and the paper's own analysis uses a finite-horizon approximation.
Experimental setup
Datasets: NYC High Volume For-Hire Vehicle trip records (Manhattan, July 2024) NYC FHV trip records (Queens, July 2024)
Benchmarks: Manhattan ride-hailing test set (24 half-hour episodes, July 18, 2024) Queens FHV dataset (July 17, 2024)
Metrics: reward service rate delivery time detour time pickup time confirmation time
Baselines: DeepPool BMG-Q HIVES Enders et al. (MASAC) CEVD Hoppe et al. (COMA) IPPO MAPPO IPG
Builds on: GRPO PPO IPPO MAPPO DeepPool
Closest papers by meaning
- GARLIC: GPT-Augmented Reinforcement Learning with Intelligent Control for Vehicle Dispatching (AAAI 2025 · similarity 0.89)
- NondBREM: Nondeterministic Offline Reinforcement Learning for Large-Scale Order Dispatching (AAAI 2024 · similarity 0.88)
- URB - Urban Routing Benchmark for RL-equipped Connected Autonomous Vehicles (NeurIPS 2025 · similarity 0.87)
- i-Rebalance: Personalized Vehicle Repositioning for Supply Demand Balance (AAAI 2024 · similarity 0.87)
- Hierarchical Optimization via LLM-Guided Objective Evolution for Mobility-on-Demand Systems (NeurIPS 2025 · similarity 0.87)
- Advancing Multi-agent Traffic Simulation via R1-Style Reinforcement Fine-Tuning (ICLR 2026 · similarity 0.86)
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